National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule

[Federal Register: January 5, 2006 (Volume 71, Number 3)]
[Rules and Regulations]
[Page 653-702]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr05ja06-5]
[[Page 654]]

-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 9, 141, and 142
[EPA-HQ-OW-2002-0039; FRL-8013-1]
RIN 2040--AD37

National Primary Drinking Water Regulations: Long Term 2 Enhanced
Surface Water Treatment Rule

AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: EPA is promulgating National Primary Drinking Water
Regulations that require the use of treatment techniques, along with
monitoring, reporting, and public notification requirements, for all
public water systems that use surface water sources. The purposes of
the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) are to
protect public health from illness due to Cryptosporidium and other
microbial pathogens in drinking water and to address risk-risk trade-
offs with the control of disinfection byproducts.
Key provisions in the LT2ESWTR include the following: source water
monitoring for Cryptosporidium, with a screening procedure to reduce
monitoring costs for small systems; risk-targeted Cryptosporidium
treatment by filtered systems with the highest source water
Cryptosporidium levels; inactivation of Cryptosporidium by all
unfiltered systems; criteria for the use of Cryptosporidium treatment
and control processes; and covering or treating uncovered finished
water storage facilities.
EPA believes that implementation of the LT2ESWTR will significantly
reduce levels of infectious Cryptosporidium in finished drinking water.
This will substantially lower rates of endemic cryptosporidiosis, the
illness caused by Cryptosporidium, which can be severe and sometimes
fatal in sensitive subpopulations (e.g., infants, people with weakened
immune systems). In addition, the treatment technique requirements of
this regulation will increase protection against other microbial
pathogens like Giardia lamblia.

DATES: This final rule is effective on March 6, 2006. The incorporation
by reference of certain publications listed in the rule is approved by
the Director of the Federal Register as of March 6, 2006. For judicial
review purposes, this final rule is promulgated as of January 5, 2006.

ADDRESSES: EPA has established a docket for this action under Docket ID
No. EPA-HQ-OW-2002-0039. All documents in the docket are listed on the
http://www.regulations.gov Web site. Although listed in the index,
some information is not publicly available, i.e., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, is not placed on the Internet and will be
publicly available only in hard copy form. Publicly available docket
materials are available either electronically through
http://www.regulations.gov or in hard copy at the Water Docket,
EPA/DC, EPA West, Room B102, 1301 Constitution Ave., NW., Washington, DC.
The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through
Friday, excluding legal holidays. The telephone number for the Public
Reading Room is (202) 566-1744, and the telephone number for the Water
Docket is (202) 566-2426.

FOR FURTHER INFORMATION CONTACT: Daniel C. Schmelling, Standards and
Risk Management Division, Office of Ground Water and Drinking Water (MC
4607M), Environmental Protection Agency, 1200 Pennsylvania Ave., NW.,
Washington, DC 20460; telephone number: (202) 564-5281; fax number:
(202) 564-3767; e-mail address: schmelling.dan@epa.gov. For general
information, contact the Safe Drinking Water Hotline, telephone number:
(800) 426-4791. The Safe Drinking Water Hotline is open Monday through
Friday, excluding legal holidays, from 9 a.m. to 5 p.m., Eastern time.

SUPPLEMENTARY INFORMATION:

I. General Information

A. Who Is Regulated by This Action?

Entities potentially regulated by the LT2ESWTR are public water
systems (PWSs) that use surface water or ground water under the direct
influence of surface water (GWUDI). Regulated categories and entities
are identified in the following chart.

------------------------------------------------------------------------
Category Examples of regulated entities
------------------------------------------------------------------------
Industry............................... Public Water Systems that use
surface water or ground water
under the direct influence of
surface water.
State, Local, Tribal or Federal Public Water Systems that use
Governments. surface water or ground water
under the direct influence of
surface water.
------------------------------------------------------------------------

This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be regulated by this
action. This table lists the types of entities that EPA is now aware
could potentially be regulated by this action. Other types of entities
not listed in this table could also be regulated. To determine whether
your facility is regulated by this action, you should carefully examine
the definition of public water system in Sec. 141.3 of Title 40 of the
Code of Federal Regulations and applicability criteria in Sec.
141.700(b) of today's rule. If you have questions regarding the
applicability of the LT2ESWTR to a particular entity, consult one of
the persons listed in the preceding section entitled FOR FURTHER
INFORMATION CONTACT.

Abbreviations Used in This Document

ASTM American Society for Testing and Materials
AWWA American Water Works Association
[deg]C Degrees Centigrade
CDC Centers for Disease Control and Prevention
CFE Combined Filter Effluent
CFR Code of Federal Regulations
COI Cost-of-Illness
CT The Residual Concentration of Disinfectant (mg/L) Multiplied by the
Contact Time (in minutes)
CWS Community Water Systems
DAPI 4',6-Diamindino-2-phenylindole
DBPs Disinfection Byproducts
DBPR Disinfectants/Disinfection Byproducts Rule
DE Diatomaceous Earth
DIC Differential Interference Contrast (microscopy)
EA Economic Analysis
EPA United States Environmental Protection Agency
GAC Granular Activated Carbon
GWUDI Ground Water Under the Direct Influence of Surface Water
HAA5 Five Haloacetic Acids (Monochloroacetic, Dichloroacetic,
Trichloroacetic, Monobromoacetic and Dibromoacetic Acids)
ICR Information Collection Rule (also Information Collection Request)
ICRSS Information Collection Rule Supplemental Surveys

[[Page 655]]

ICRSSM Information Collection Rule Supplemental Survey of Medium Systems
ICRSSL Information Collection Rule Supplemental Survey of Large Systems
IESWTR Interim Enhanced Surface Water Treatment Rule
Log Logarithm (common, base 10)
LRAA Locational Running Annual Average
LRV Log Removal Value
LT1ESWTR Long Term 1 Enhanced Surface Water Treatment Rule
LT2ESWTR Long Term 2 Enhanced Surface Water Treatment Rule
MCL Maximum Contaminant Level
MCLG Maximum Contaminant Level Goal
MG Million Gallons
M-DBP Microbial and Disinfectants/Disinfection Byproducts
MF Microfiltration
NPDWR National Primary Drinking Water Regulation
NTTAA National Technology Transfer and Advancement Act
NTU Nephelometric Turbidity Unit
OMB Office of Management and Budget
PE Performance Evaluation
PWS Public Water System
QC Quality Control
QCRV Quality Control Release Value
RAA Running Annual Average
RFA Regulatory Flexibility Act
RO Reverse Osmosis
SAB Science Advisory Board
SBAR Small Business Advocacy Review
SDWA Safe Drinking Water Act
SWAP Source Water Assessment Program
SWTR Surface Water Treatment Rule
TCR Total Coliform Rule
TTHM Total Trihalomethanes
UF Ultrafiltration
UMRA Unfunded Mandates Reform Act

Table of Contents

I. General Information
A. Who Is Regulated by This Action?
II. Summary of the Final Rule
A. Why Is EPA Promulgating the LT2ESWTR?
B. What Does the LT2ESWTR Require?
1. Source water monitoring
2. Additional treatment for Cryptosporidium
3. Uncovered finished water storage facilities
C. Will This Regulation Apply to My Water System?
III. Background Information
A. Statutory Requirements and Legal Authority
B. Existing Regulations for Microbial Pathogens in Drinking Water
1. Surface Water Treatment Rule
2. Total Coliform Rule
3. Interim Enhanced Surface Water Treatment Rule
4. Long Term 1 Enhanced Surface Water Treatment Rule
5. Filter Backwash Recycle Rule
C. Concern with Cryptosporidium in Drinking Water
1. Introduction
2. What is Cryptosporidium?
3. Cryptosporidium health effects
4. Efficacy of water treatment processes on Cryptosporidium
5. Epidemic and endemic disease from Cryptosporidium
D. Specific Concerns Following the IESWTR and LT1ESWTR
E. New Information on Cryptosporidium Risk Management
1. Infectivity
2. Occurrence
3. Analytical methods
4. Treatment
F. Federal Advisory Committee Recommendations
IV. Explanation of Today's Action
A. Source Water Monitoring Requirements
1. Today's rule
a. Sampling parameters and frequency
b. Sampling location
c. Sampling schedule
d. Plants operating only part of the year
e. Failing to monitor
f. Providing treatment instead of monitoring
g. Grandfathering previously collected data
h. Ongoing watershed assessment
i. Second round of monitoring
j. New source monitoring
2. Background and analysis
a. Sampling parameters and frequency
b. Sampling location
c. Sampling schedule
d. Plants operating only part of the year
e. Failing to monitor
f. Grandfathering previously collected data
g. Ongoing watershed assessment
h. Second round of monitoring
3. Summary of major comments
a. Sampling parameters and frequency
b. Sampling location
c. Sampling schedule
d. Plants operating only part of the year
e. Failing to monitor
f. Providing treatment instead of monitoring
g. Grandfathering previously collected data
h. Ongoing watershed assessment
i. Second round of monitoring
j. New source monitoring
B. Filtered System Cryptosporidium Treatment Requirements
1. Today's rule
a. Bin classification
b. Bin treatment requirements
2. Background and analysis
a. Basis for targeted treatment requirements
b. Basis for bin concentration ranges and treatment requirements
3. Summary of major comments
C. Unfiltered System Cryptosporidium Treatment Requirements
1. Today's rule
a. Determination of mean Cryptosporidium level
b. Cryptosporidium treatment requirements
c. Use of two disinfectants
2. Background and analysis
a. Basis for Cryptosporidium treatment requirements
b. Basis for requiring the use of two disinfectants
c. Filtration avoidance
3. Summary of major comments
D. Options for Systems to Meet Cryptosporidium Treatment Requirements
1. Microbial toolbox overview
2. Watershed control program
a. Today's rule
b. Background and analysis
c. Summary of major comments
3. Alternative source
a. Today's rule
b. Background and analysis
c. Summary of major comments
4. Pre-sedimentation with coagulant
a. Today's rule
b. Background and analysis
c. Summary of major comments
5. Two-stage lime softening
a. Today's rule
b. Background and analysis
c. Summary of major comments
6. Bank filtration
a. Today's rule
b. Background and analysis
c. Summary of major comments
7. Combined filter performance
a. Today's rule
b. Background and analysis
c. Summary of major comments
8. Individual filter performance
a. Today's rule
b. Background and analysis
c. Summary of major comments
9. Demonstration of performance
a. Today's rule
b. Background and analysis
c. Summary of major comments
10. Bag and cartridge filtration
a. Today's rule
b. Background and analysis
c. Summary of major comments
11. Membrane filtration
a. Today's rule
b. Background and analysis
c. Summary of major comments
12. Second stage filtration
a. Today's rule
b. Background and analysis
c. Summary of major comments
13. Slow sand filtration
a. Today's rule
b. Background and analysis
c. Summary of major comments
14. Ozone and chlorine dioxide
a. Today's rule
b. Background and analysis
c. Summary of major comments
15. Ultraviolet light
a. Today's rule
b. Background and analysis
c. Summary of major comments
E. Disinfection Benchmarking for Giardia lamblia and Viruses
1. Today's rule
2. Background and analysis
3. Summary of major comments
F. Requirements for Systems with Uncovered Finished Water
Storage Facilities
1. Today's rule

[[Page 656]]

2. Background and analysis
a. Types and sources of contaminants in open reservoirs
b. Regulatory approaches to reduce risk from contamination in
open reservoirs
c. Definition of uncovered finished water storage facility
3. Summary of major comments
G. Compliance Schedules
1. Today's rule
2. Background and analysis
3. Summary of major comments
H. Public Notice Requirements
1. Today's rule
2. Background and analysis
3. Summary of major comments
I. Reporting Source Water Monitoring Results
1. Today's rule
2. Background and analysis
3. Summary of major comments
J. Analytical Methods
1. Analytical methods overview
2. Cryptosporidium methods
a. Today's rule
b. Background and analysis
c. Summary of major comments
3. E. coli methods
a. Today's rule
b. Background and analysis
c. Summary of major comments
4. Turbidity methods
a. Today's rule
b. Background and analysis
c. Summary of major comments
K. Laboratory Approval
1. Cryptosporidium laboratory approval
a. Today's rule
b. Background and analysis
c. Summary of major comments
2. E. coli laboratory approval
a. Today's rule
b. Background and analysis
c. Summary of major comments
3. Turbidity analyst approval
a. Today's rule
b. Background and analysis
c. Summary of major comments
L. Requirements for Sanitary Surveys Conducted by EPA
1. Today's rule
2. Background and analysis
3. Summary of major comments
M. Variances and Exemptions
1. Variances
2. Exemptions
V. State Implementation
A. Today's Rule
1. Special State primacy requirements
2. State recordkeeping requirements
3. State reporting requirements
4. Interim primacy
B. Background and Analysis
C. Summary of Major Comments
VI. Economic Analysis
A. What Regulatory Alternatives Did the Agency Consider?
B. What Analyses Support Today's Final Rule?
C. What Are the Benefits of the LT2ESWTR?
1. Nonquantified benefits
2. Quantified benefits
a. Filtered PWSs
b. Unfiltered PWSs
3. Timing of benefits accrual (latency)
D. What Are the Costs of the LT2ESWTR?
1. Total annualized present value costs
2. PWS costs
a. Source water monitoring costs
b. Filtered PWSs treatment costs
c. Unfiltered PWSs treatment costs
d. Uncovered finished water storage facilities
e. Future monitoring costs
f. Sensitivity analysis--influent bromide levels on technology
selection for filtered plants
3. State/Primacy agency costs
4. Non-quantified costs
E. What Are the Household Costs of the LT2ESWTR?
F. What Are the Incremental Costs and Benefits of the LT2ESWTR?
H. Are there Increased Risks From Other Contaminants?
I. What Are the Effects of the Contaminant on the General
Population and Groups within the General Populations that Are
Identified as Likely to be at Greater Risk of Adverse Health Effects?
J. What Are the Uncertainties in the Risk, Benefit, and Cost
Estimates for the LT2ESWTR?
K. What Is the Benefit/Cost Determination for the LT2ESWTR?
L. Summary of Major Comments
1. Cryptosporidium occurrence
a. Quality of the ICR and ICRSS data sets
b. Treatment of observed zeros
2. Drinking water consumption
3. Cryptosporidium infectivity
4. Valuation of benefits
a. Valuation of morbidity
b. Valuation of lost time under the enhanced cost of illness
(COI) approach
VII. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review
B. Paperwork Reduction Act
C. Regulatory Flexibility Act
D. Unfunded Mandates Reform Act
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children from
Environmental Health and Safety Risks
H. Executive Order 13211: Actions that Significantly Affect
Energy Supply, Distribution, or Use
I. National Technology Transfer and Advancement Act
J. Executive Order 12898: Federal Actions to Address
Environmental Justice in Minority Populations or Low-Income Populations
K. Consultations with the Science Advisory Board, National
Drinking Water Advisory Council, and the Secretary of Health and
Human Services
L. Plain Language
M. Analysis of the Likely Effect of Compliance with the LT2ESWTR
on the Technical, Financial, and Managerial Capacity of Public Water
Systems
N. Congressional Review Act
VIII. References

II. Summary of the Final Rule

A. Why Is EPA Promulgating the LT2ESWTR?

EPA is promulgating the Long Term 2 Enhanced Surface Water
Treatment Rule (LT2ESWTR) to further protect public health against
Cryptosporidium and other microbial pathogens in drinking water.
Cryptosporidium is a protozoan parasite that is common in surface water
used as drinking water sources by public water systems (PWSs). In
drinking water, Cryptosporidium is a particular concern because it is
highly resistant to chemical disinfectants like chlorine. When
ingested, Cryptosporidium can cause acute gastrointestinal illness,
which may be severe and sometimes fatal for people with weakened immune
systems. Cryptosporidium has been identified as the cause of a number
of waterborne disease outbreaks in the United States (details in
section III.C).
The LT2ESWTR supplements existing microbial treatment regulations
and targets PWSs with higher potential risk from Cryptosporidium.
Existing regulations require most PWSs using surface water sources to
filter the water, and those PWSs that are required to filter must
remove at least 99 percent (2-log) of the Cryptosporidium (details in
section III.B). As explained in the proposal for today's rule (68 FR
47640, August 11, 2003) (USEPA 2003a), new data on the occurrence,
infectivity, and treatment of Cryptosporidium in drinking water
indicate that existing regulations are sufficient for most PWSs. A
subset of PWSs with greater vulnerability to Cryptosporidium, however,
requires additional treatment.
In particular, recent national survey data show that the level of
Cryptosporidium in the sources of most filtered PWSs is lower than
previously estimated, but also that Cryptosporidium levels vary widely
from source to source. Accordingly, a subset of filtered PWSs has
relatively high levels of source water Cryptosporidium contamination.
In addition, data from human health studies indicate that the potential
for Cryptosporidium to cause infection is likely greater than
previously recognized (details in section III.E). These findings have
led EPA to conclude that existing requirements do not provide adequate
public health protection in filtered PWSs with the highest source water
Cryptosporidium levels. Consequently, EPA is establishing risk-targeted
additional treatment requirements for such filtered PWSs under the
LT2ESWTR.

[[Page 657]]

For PWSs that use surface water sources and are not required to
filter (i.e., unfiltered PWSs), existing regulations do not require any
treatment for Cryptosporidium. New survey data suggest that typical
Cryptosporidium levels in the treated water of unfiltered PWSs are
higher than in the treated water of filtered PWSs (USEPA 2003a). Thus,
Cryptosporidium treatment by unfiltered PWSs is needed to achieve
comparable public health protection (details in section III.E).
Further, results from recent treatment studies have allowed EPA to
develop standards for the inactivation of Cryptosporidium by ozone,
ultraviolet (UV) light, and chlorine dioxide (details in section IV.D).
Based on these developments, EPA is establishing requirements under the
LT2ESWTR for all unfiltered PWSs to treat for Cryptosporidium, with the
required degree of treatment depending on the source water
contamination level.
Additionally, the LT2ESWTR addresses risks in uncovered finished
water storage facilities, in which treated water can be subject to
significant contamination as a result of runoff, bird and animal
wastes, human activity, algal growth, insects, fish, and airborne
deposition (details in section IV.F). Existing regulations prohibit the
building of new uncovered finished water storage facilities but do not
deal with existing ones. Under the LT2ESWTR, PWSs must limit potential
risks by covering or treating the discharge of such storage facilities.
Most of the requirements in today's final LT2ESWTR reflect
consensus recommendations from the Stage 2 Microbial and Disinfection
Byproducts (M-DBP) Federal Advisory Committee. These recommendations
are set forth in the Stage 2 M-DBP Agreement in Principle (65 FR 83015,
December 29, 2000) (USEPA 2000a).

B. What Does the LT2ESWTR Require?

1. Source Water Monitoring
The LT2ESWTR requires PWSs using surface water or ground water
under the direct influence (GWUDI) of surface water to monitor their
source water (i.e., the influent water entering the treatment plant) to
determine an average Cryptosporidium level. As described in the next
section, monitoring results determine the extent of Cryptosporidium
treatment requirements under the LT2ESWTR.
Large PWSs (serving at least 10,000 people) must monitor for
Cryptosporidium (plus E. coli and turbidity in filtered PWSs) for a
period of two years. To reduce monitoring costs, small filtered PWSs
(serving fewer than 10,000 people) initially monitor just for E. coli
for one year as a screening analysis and are required to monitor for
Cryptosporidium only if their E. coli levels exceed specified
``trigger'' values. Small filtered PWSs that exceed the E. coli
trigger, as well as all small unfiltered PWSs, must monitor for
Cryptosporidium for one or two years, depending on the sampling
frequency (details sections IV.A).
Under the LT2ESWTR, specific criteria are set for sampling
frequency and schedule, sampling location, using previously collected
data (i.e., grandfathering), providing treatment instead of monitoring,
sampling by PWSs that use surface water for only part of the year, and
monitoring of new plants and sources (details in section IV.A). The
LT2ESWTR also establishes requirements for reporting of monitoring
results (details in section IV.I), using analytical methods (details in
section IV.J), and using approved laboratories (details in section IV.K).
The date for PWSs to begin monitoring is staggered by PWS size,
with smaller PWSs starting at a later time than larger ones (details in
section IV.G). Today's rule also requires a second round of monitoring
to begin approximately 6.5 years after the first round concludes in
order to determine if source water quality has changed to a degree that
should affect treatment requirements (details in section IV.A).
2. Additional Treatment for Cryptosporidium
The LT2ESWTR establishes risk-targeted treatment technique
requirements to control Cryptosporidium in PWSs using surface water or
GWUDI. These treatment requirements supplement those established by
existing regulations, all of which remain in effect under the LT2ESWTR.
Filtered PWSs will be classified in one of four treatment
categories (or ``bins'') based on the results of the source water
Cryptosporidium monitoring described in the previous section. This bin
classification determines the degree of additional Cryptosporidium
treatment, if any, the filtered PWS must provide. Occurrence data
indicate that the majority of filtered PWSs will be classified in Bin
1, which carries no additional treatment requirements. PWSs classified
in Bins 2, 3, or 4 must achieve 1.0- to 2.5-log of treatment (i.e., 90
to 99.7 percent reduction) for Cryptosporidium over and above that
provided with conventional treatment. Different additional treatment
requirements may apply to PWSs using other than conventional treatment,
such as direct filtration, membranes, or cartridge filters (details in
section. IV.B). Filtered PWSs must meet the additional Cryptosporidium
treatment required in Bins 2, 3, or 4 by using one or more treatment or
control processes from a ``microbial toolbox'' of options (details in
section. IV.D).
The LT2ESWTR requires all unfiltered PWSs to provide at least 2-log
(i.e., 99 percent) inactivation of Cryptosporidium. If the average
source water Cryptosporidium level exceeds 0.01 oocysts/L based on the
monitoring described in the previous section, the unfiltered PWS must
provide at least 3-log (i.e., 99.9 percent) inactivation of
Cryptosporidium. Further, under the LT2ESWTR, unfiltered PWSs must
achieve their overall inactivation requirements (including Giardia
lamblia and virus inactivation as established by earlier regulations)
using a minimum of two disinfectants (details in section IV.C).
3. Uncovered Finished Water Storage Facilities
Under the LT2ESWTR, PWSs with uncovered finished water storage
facilities must take steps to address contamination risks. Existing
regulations require PWSs to cover all new storage facilities for
finished water but do not address existing uncovered finished water
storage facilities. Under the LT2ESWTR, PWSs using uncovered finished
water storage facilities must either cover the storage facility or
treat the storage facility discharge to achieve inactivation and/or
removal of 4-log virus, 3-log Giardia lamblia, and 2-log
Cryptosporidium on a State-approved schedule (details in section.
IV.F).

C. Will This Regulation Apply to My Water System?

The LT2ESWTR applies to all PWSs using surface water or GWUDI,
including both large and small PWSs, community and non-community PWSs,
and non-transient and transient PWSs. Wholesale PWSs must comply with
the requirements of today's rule based on the population of the largest
PWS in the combined distribution system. Consecutive PWSs that purchase
treated water from wholesale PWSs that fully comply with the monitoring
and treatment requirements of the LT2ESWTR are not required to take
additional steps for that water under today's rule.

III. Background Information

The sections in this part provide summary background information for

[[Page 658]]

today's final LT2ESWTR. Individual sections address the following
topics: (A) Statutory requirements and legal authority for the
LT2ESWTR; (B) existing regulations for microbial pathogens in drinking
water; (C) the problem with Cryptosporidium in drinking water; (D)
specific public health concerns addressed by the LT2ESWTR; (E) new
information for Cryptosporidium risk management in PWSs; and (F)
recommendations from the Stage 2 M-DBP Advisory Committee for the
LT2ESWTR. For additional information on these topics, see the proposed
LT2ESWTR (USEPA 2003a) and supporting technical material where cited.

A. Statutory Requirements and Legal Authority

The Safe Drinking Water Act (SDWA or the Act), as amended in 1996,
requires EPA to publish a maximum contaminant level goal (MCLG) and
promulgate a national primary drinking water regulation (NPDWR) with
enforceable requirements for any contaminant that the Administrator
determines may have an adverse effect on the health of persons, is
known to occur or has a substantial likelihood of occurring in public
water systems (PWSs) with a frequency and at levels of public health
concern, and for which, in the sole judgement of the Administrator,
regulation of such contaminant presents a meaningful opportunity for
health risk reduction for persons served by PWSs (section 1412 (b)(1)(A)).
MCLGs are non-enforceable health goals and are to be set at a level
at which no known or anticipated adverse effects on the health of
persons occur and which allows an adequate margin of safety (sections
1412(b)(4) and 1412(a)(3)). EPA established an MCLG of zero for
Cryptosporidium under the Interim Enhanced Surface Water Treatment Rule
(IESWTR) (63 FR 69478, December 16, 1998) (USEPA 1998a). In today's
rule, the Agency is not making any changes to the current MCLG for
Cryptosporidium.
The Act also requires each NPDWR for which an MCLG is established
to specify a maximum contaminant level (MCL) that is as close to the
MCLG as is feasible (sections 1412(b)(4) and 1401(1)(C)). The Agency is
authorized to promulgate an NPDWR that requires the use of a treatment
technique in lieu of establishing an MCL if the Agency finds that it is
not economically or technologically feasible to ascertain the level of
the contaminant (sections 1412(b)(7)(A) and 1401(1)(C)). The Act
specifies that in such cases, the Agency shall identify those treatment
techniques that would prevent known or anticipated adverse effects on
the health of persons to the extent feasible (section 1412(b)(7)(A)).
The Agency has concluded that it is not currently economically or
technologically feasible for PWSs to determine the level of
Cryptosporidium in finished drinking water for the purpose of
compliance with a finished water standard. As described in section
IV.C, the LT2ESWTR is designed to protect public health by lowering the
level of infectious Cryptosporidium in finished drinking water to less
than 1 oocyst/10,000 L. Approved Cryptosporidium analytical methods,
which are described in section IV.K, are not sufficient to routinely
determine the level of Cryptosporidium at this concentration.
Consequently, the LT2ESWTR relies on treatment technique requirements
to reduce health risks from Cryptosporidium in PWSs.
When proposing an NPDWR that includes an MCL or treatment
technique, the Act requires EPA to publish and seek public comment on
an analysis of health risk reduction and costs. This includes an
analysis of quantifiable and nonquantifiable costs and health risk
reduction benefits, incremental costs and benefits of each alternative
considered, the effects of the contaminant upon sensitive
subpopulations (e.g., infants, children, pregnant women, the elderly,
and individuals with a history of serious illness), any increased risk
that may occur as the result of compliance, and other relevant factors
(section 1412(b)(3)(C)). EPA's analysis of health benefits and costs
associated with the LT2ESWTR is presented in the Economic Analysis of
the LT2ESWTR (USEPA 2005a) and is summarized in section VI of this
preamble. The Act does not, however, authorize the Administrator to use
a determination of whether benefits justify costs to establish an MCL
or treatment technique requirement for the control of Cryptosporidium
(section 1412(b)(6)(C)).
Finally, section 1412(b)(2)(C) of the Act requires EPA to
promulgate a Stage 2 Disinfectants and Disinfection Byproducts Rule
within 18 months after promulgation of the LT1ESWTR, which occurred on
January 14, 2002. Consistent with statutory requirements for risk
balancing (section 1412(b)(5)(B)), EPA is finalizing the LT2ESWTR in
conjunction with the Stage 2 DBPR to ensure parallel protection from
microbial and DBP risks.

B. Existing Regulations for Microbial Pathogens in Drinking Water

This section summarizes existing rules that regulate treatment for
pathogenic microorganisms by PWSs using surface water sources. The
LT2ESWTR supplements these rules with additional risk-targeted
requirements, but does not withdraw any existing requirements.
1. Surface Water Treatment Rule
The Surface Water Treatment Rule (SWTR) (54 FR 27486, June 29,
1989) (USEPA 1989a) applies to all PWSs using surface water or ground
water under the direct influence (GWUDI) of surface water as sources
(i.e., Subpart H PWSs). It established MCLGs of zero for Giardia
lamblia, viruses, and Legionella, and includes the following treatment
technique requirements to reduce exposure to pathogenic microorganisms:
(1) Filtration, unless specific avoidance criteria are met; (2)
maintenance of a disinfectant residual in the distribution system; (3)
removal and/or inactivation of 3-log (99.9%) of Giardia lamblia and 4-
log (99.99%) of viruses; (4) maximum allowable turbidity in the
combined filter effluent (CFE) of 5 nephelometric turbidity units (NTU)
and 95th percentile CFE turbidity of 0.5 NTU or less for plants using
conventional treatment or direct filtration (with different standards
for other filtration technologies); and (5) watershed protection and
source water quality requirements for unfiltered PWSs.
2. Total Coliform Rule
The Total Coliform Rule (TCR) (54 FR 27544, June 29, 1989) (USEPA
1989b) applies to all PWSs. It established an MCLG of zero for total
and fecal coliform bacteria and an MCL based on the percentage of
positive samples collected during a compliance period. Coliforms are
used as an indicator of fecal contamination and to determine the
integrity of the water treatment process and distribution system. Under
the TCR, no more than 5 percent of distribution system samples
collected in any month may contain coliform bacteria (no more than 1
sample per month may be coliform positive in those PWSs that collect
fewer than 40 samples per month). The number of samples to be collected
in a month is based on the number of people served by the PWS.
3. Interim Enhanced Surface Water Treatment Rule
The Interim Enhanced Surface Water Treatment Rule (IESWTR) (63 FR
69478, December 16, 1998) (USEPA 1998a) applies to PWSs serving at
least 10,000 people and using surface water or

[[Page 659]]

GWUDI sources. Key provisions established by the IESWTR include the
following: (1) An MCLG of zero for Cryptosporidium; (2) Cryptosporidium
removal requirements of 2-log (99 percent) for PWSs that filter; (3)
more stringent CFE turbidity performance standards of 1.0 NTU as a
maximum and 0.3 NTU or less at the 95th percentile monthly for
treatment plants using conventional treatment or direct filtration; (4)
requirements for individual filter turbidity monitoring; (5)
disinfection benchmark provisions to assess the level of microbial
protection that PWSs provide as they take steps to comply with new DBP
standards; (6) inclusion of Cryptosporidium in the definition of GWUDI
and in the watershed control requirements for unfiltered PWSs; (7)
requirements for covers on new finished water storage facilities; and
(8) sanitary surveys for all surface water systems regardless of size.
The IESWTR was developed in conjunction with the Stage 1
Disinfectants and Disinfection Byproducts Rule (Stage 1 DBPR) (63 FR
69389, December 16, 1998) (USEPA 1998b), which reduced allowable levels
of certain DBPs, including trihalomethanes, haloacetic acids, chlorite,
and bromate.
4. Long Term 1 Enhanced Surface Water Treatment Rule
The Long Term 1 Enhanced Surface Water Treatment Rule ( LT1ESWTR)
(67 FR 1812, January 14, 2002) (USEPA 2002a) builds upon the microbial
control provisions established by the IESWTR for large PWSs through
extending similar requirements to small PWSs. The LT1ESWTR applies to
PWSs that use surface water or GWUDI as sources and that serve fewer
than 10,000 people. Like the IESWTR, the LT1ESWTR established the
following: 2-log (99 percent) Cryptosporidium removal requirements by
PWSs that filter; individual filter turbidity monitoring and more
stringent combined filter effluent turbidity standards for conventional
and direct filtration plants; disinfection profiling and benchmarking;
inclusion of Cryptosporidium in the definition of GWUDI and in the
watershed control requirements for unfiltered PWSs; and the requirement
that new finished water storage facilities be covered.
5. Filter Backwash Recycle Rule
The Filter Backwash Recycling Rule (FBRR) (66 FR 31085, June 8,
2001) (USEPA 2001a) requires PWSs to consider the potential risks
associated with recycling contaminants removed during the filtration
process. The provisions of the FBRR apply to all PWSs that recycle,
regardless of population served. In general, the provisions include the
following: (1) PWSs must return certain recycle streams to a point in
the treatment process that is prior to primary coagulant addition
unless the State specifies an alternative location; (2) direct
filtration PWSs recycling to the treatment process must provide
detailed recycle treatment information to the State; and (3) certain
conventional PWSs that practice direct recycling must perform a one-
month, one-time recycling self assessment.

C. Concern With Cryptosporidium in Drinking Water

1. Introduction
EPA is promulgating the LT2ESWTR to reduce the public health risk
associated with Cryptosporidium in drinking water. This section
describes the general basis for this public health concern through
reviewing information in several areas: the nature of Cryptosporidium,
health effects, efficacy of water treatment processes, and the
incidence of epidemic and endemic disease. Further information about
Cryptosporidium is available in the following documents:
Cryptosporidium: Human Health Criteria Document (USEPA 2001b),
Cryptosporidium: Drinking Water Advisory (USEPA 2001c), and
Cryptosporidium: Risks for Infants and Children (USEPA 2001d).
2. What Is Cryptosporidium?
Cryptosporidium is a protozoan parasite that lives and reproduces
entirely in one host. Ingestion of Cryptosporidium can cause
cryptosporidiosis, a gastrointestinal (GI) illness. Cryptosporidium is
excreted in feces. Transmission of cryptosporidiosis occurs through
consumption of water or food contaminated with feces or by direct or
indirect contact with infected persons or animals (Casemore 1990).
In the environment, Cryptosporidium is present as a thick-walled
oocyst containing four organisms (sporozoites); the oocyst wall
insulates the sporozoites from harsh environmental conditions. Oocysts
are 4-5 microns in length and width. Upon a host's ingestion of
oocysts, enzymes and chemicals produced by the host's digestive system
cause the oocyst to excyst, or break open. The excysted sporozoites
embed themselves in the surfaces of the epithelial cells of the lower
small intestine. The organisms then begin absorbing nutrients from
their host cells. When these organisms sexually reproduce, they produce
thick- and thin-walled oocysts. The host excretes the thick-walled
oocysts in its feces; thin-walled oocysts excyst within the host and
contribute to further host infection.
The exact mechanism by which Cryptosporidium causes GI illness is
not known. Factors may include damage to intestinal structure and
cells, changes in the absorption/secretion processes of the intestine,
toxins produced by Cryptosporidium or the host, and proteins that allow
Cryptosporidium to adhere to host cell surfaces (Carey et al. 2004).
Upon excretion, Cryptosporidium oocysts may survive for months in
various environmental media, including soil, river water, seawater, and
human and cattle feces at ambient temperatures (Kato et al. 2001,
Pokorny et al. 2002, Fayer et al. 1998a and 1998b, and Robertson et al.
1992). Cryptosporidium can also withstand temperatures as low as -20
[deg]C for periods of a few hours (Fayer and Nerad 1996) but are
susceptible to desiccation (Robertson et al. 1992).
Cryptosporidium is a widespread contaminant in surface water used
as drinking water supplies. For example, among 67 drinking water
sources surveyed by LeChevallier and Norton (1995), 87 percent had
positive samples for Cryptosporidium. A more recent survey of 80 medium
and large PWSs conducted by EPA detected Cryptosporidium in 85 percent
of water sources (USEPA 2003a). Cryptosporidium contamination can come
from animal agriculture, wastewater treatment plant discharges,
slaughterhouses, birds, wild animals, and other sources of fecal matter.
Because different species of Cryptosporidium are very similar in
morphology, researchers have focused on genetic differences in trying
to classify them. However, discussion on Cryptosporidium taxonomy is
complicated by the fact that even within species or strains, there may
be differences in infectivity and virulence. Cryptosporidium parvum (C.
parvum) has been the primary species of concern to humans. Until
recently, some researchers divided C. parvum into two primary strains,
genotype 1, which infects humans, and genotype 2, which infects both
humans and cattle (Carey et al. 2004). In 2002, Morgan-Ryan et al.
proposed that genotype 1 be designated a separate species, C. hominis.
Additional Cryptosporidium species infecting other mammals, birds, and
reptiles have been documented. In some cases, these species can infect
both immunocompromised (having weakened immune systems) and

[[Page 660]]

otherwise healthy humans (Carey et al. 2004).
3. Cryptosporidium Health Effects
Cryptosporidium infection is characterized by mild to severe
diarrhea, dehydration, stomach cramps, and/or a slight fever.
Incubation is thought to range from 2 to 10 days (Arrowood 1997).
Symptoms typically last from several days to 2 weeks, though in a small
percentage of cases, the symptoms may persist for months or longer in
otherwise healthy individuals.
Symptoms may be more severe in immunocompromised persons (Frisby et
al. 1997, Carey et al. 2004). Such persons include those with AIDS,
cancer patients undergoing chemotherapy, organ transplant recipients
treated with drugs that suppress the immune system, and patients with
autoimmune disorders (e.g., Lupus). In AIDS patients, Cryptosporidium
has been found in the lungs, ear, stomach, bile duct, and pancreas in
addition to the small intestine (Farthing 2000). Immunocompromised
patients with severe persistent cryptosporidiosis may die (Carey et al.
2004). Besides the immunocompromised, children and the elderly may be
at higher risk from Cryptosporidium than the general population
(discussed in section VII.G).
Studies with human volunteers have demonstrated that a low dose of
C. parvum (e.g., 10 oocysts) is sufficient to cause infection in
healthy adults, although some strains are more infectious than others
(DuPont et al. 1995, Chappell et al. 1999, Okhuysen et al. 2002).
Studies of immunosuppressed adult mice have demonstrated that a single
viable oocyst can induce C. parvum infections (Yang et al. 2000,
Okhuysen et al. 2002). The lowest dose tested in any of the human
challenge studies was 10 oocysts. Because drinking water exposures are
generally projected to be at lower levels (e.g., 1 oocyst), statistical
modeling is necessary to project the effects of such exposure.
Following the advice of its Science Advisory Board (SAB), EPA has
developed a range of models to predict effects of exposure to low doses
of Cryptosporidium. These models are discussed in section VI and in the
LT2ESWTR Economic Analysis (USEPA 2005a).
The degree and duration of the immune response to Cryptosporidium
is not well characterized. In a study by Chappell et al. (1999),
volunteers with IgG Cryptosporidium antibodies in their blood were
immune to low doses of oocysts. The ID50 (the dose that infects 50
percent of the challenged population) was 1,880 oocysts for those
individuals compared to 132 oocysts for individuals that tested
negative for those antibodies. However, earlier studies did not observe
a correlation between the development of antibodies after
Cryptosporidium infection and subsequent protection from illness
(Okhuysen et al. 1998).
No cure for cryptosporidiosis is known. Medical care usually
involves treatment for dehydration and nutrient loss. Certain
antimicrobial drugs like Azithromycin, Paromomycin, and nitazoxanide,
the only drug approved for cryptosporidiosis in children, have been
partially effective in treating immunocompromised patients (Rossignol
et al. 1998). Therapies used to treat retroviruses can be helpful in
fighting cryptosporidiosis in people with AIDS and are more effective
when used in conjunction with antimicrobial therapy. The effectiveness
of antiretroviral therapy is thought to be related to the associated
increase in white blood cells rather than the decrease in the amount of
virus present.
4. Efficacy of Water Treatment Processes on Cryptosporidium
EPA is particularly concerned about Cryptosporidium because, unlike
pathogens such as bacteria and most viruses, Cryptosporidium oocysts
are highly resistant to standard disinfectants like chlorine and
chloramines (Korich et al. 1990, Ransome et al. 1993, Finch et al.
1997). Consequently, control of Cryptosporidium in most treatment
plants is dependent on physical removal processes. However, due to
their size (4-5 microns), oocysts can sometimes pass through filters.
Monitoring data on finished water show that Cryptosporidium is
sometimes present in filtered, treated drinking water (LeChevallier et
al. 1991, Aboytes et al. 2004). For example, Aboytes et al. (2004)
analyzed 1,690 finished water samples from 82 plants. Of these, 22
plants had at least one positive sample for infectious Cryptosporidium
(1.4 percent of all samples were positive). All positive samples
occurred at plants that met existing regulatory standards and many had
very low turbidity.
Waterborne outbreaks of cryptosporidiosis have occurred even in
areas served by filtered surface water supplies (Solo-Gabriele and
Neumeister, 1996). In some cases, outbreaks were attributed to
treatment deficiencies, but in others, the treatment provided by the
water system met the regulatory requirements in place at that time.
These data indicate that even surface water systems that filter and
disinfect can still be vulnerable to Cryptosporidium, depending on the
source water quality and treatment effectiveness.
Certain alternative disinfectants can be more effective in treating
for Cryptosporidium. Both ozone and chlorine dioxide have been shown to
inactivate Cryptosporidium, albeit at doses much higher than those
required to inactivate Giardia, which has typically been used to set
disinfectant doses (summarized in USEPA 2003a). Studies have also
demonstrated a synergistic effect of treatment using ozone followed by
chlorine or monochloramine (Rennecker et al. 2000, Driedger et al.
2001). Significantly, UV light has recently been shown to achieve high
levels of Cryptosporidium inactivation at feasible doses (summarized in
USEPA 2003a).
Other processes that can help reduce Cryptosporidium levels in
finished water include watershed management programs, pretreatment
processes like bank filtration, and additional clarification and
filtration processes during water treatment. Further, optimizing
treatment performance and achieving very low levels of turbidity in the
finished water has been shown to improve Cryptosporidium removal in
treatment plants (summarized in USEPA 2003a).
5. Epidemic and Endemic Disease From Cryptosporidium
Cryptosporidium has caused a number of waterborne disease outbreaks
since 1984 when the first was reported in the United States. Data from
the Centers for Disease Control and Prevention (CDC) include ten
outbreaks caused by Cryptosporidium in drinking water between 1984 and
2000, with approximately 421,000 cases of illness (CDC 1993, 1996,
1998, 2000, and 2002). The most serious outbreak occurred in 1993 in
Milwaukee; an estimated 403,000 people became sick (MacKenzie et al.
1994), and at least 50 Cryptosporidium-associated deaths occurred among
the severely immunocompromised (Hoxie et al. 1997). Further, a study by
McDonald et al. (2001) using blood samples from Milwaukee children
suggests that Cryptosporidium infection was more widespread than might
be inferred from the illness estimates by MacKenzie et al. (1994).
The number of identified and reported outbreaks in the CDC database
is believed to substantially understate the actual incidence of
waterborne disease outbreaks and cases (Craun and Calderon 1996,
National Research Council 1997). This under reporting is

[[Page 661]]

due to a number of factors. Many people experiencing gastrointestinal
illness do not seek medical attention. Where medical attention is
provided, the pathogenic agent may not be identified through routine
testing. Physicians and patients often lack sufficient information to
attribute gastrointestinal illness to any specific origin, such as
drinking water, and few States have an active outbreak surveillance
program. In addition, if drinking water is investigated as the source
of an outbreak, oocysts may not be detected in water samples even if
they are present, due to limitations in analytical methods.
Consequently, outbreaks may not be recognized in a community or, if
recognized, may not be traced to a drinking water source.
In addition, an unknown but probably significant portion of
waterborne disease is endemic (i.e., isolated cases not associated with
an outbreak) and, thus, is even more difficult to recognize. In an
outbreak, if the pathogen has been identified, medical providers and
public health investigators know what to look for. In endemic disease,
there is no investigation, so the illness may never be identified, or
if it is, it may not be linked to a source (e.g., drinking water,
person-to-person transmission). In addition, where a pathogen is
identified, lab results may not be reported to public health agencies.
Because of this under reporting, the actual incidence of
cryptosporidiosis associated with drinking water is unknown. However,
indications of this incidence rate can be roughly extrapolated from
different sources. Mead et al. (1999) estimated approximately 300,000
total cases of cryptosporidiosis annually that result in a physician
visit, with 90 percent of these attributed to waterborne (drinking
water and recreational water) and secondary transmission. This estimate
is based on the percentage of stools that test positive for
Cryptosporidium and applying this percentage to the approximately 15
million physician visits for diarrhea each year. While the fraction of
cryptosporidiosis cases that result in a physician visit is unknown,
Corso et al. (2003) reported that during the 1993 outbreak in
Milwaukee, medical care was sought in approximately 12 percent of all
cryptosporidiosis cases.
Surveillance data from the CDC for 2001 show an overall incidence
of 1.5 laboratory diagnosed cases of cryptosporidiosis per 100,000
population (CDC, 2002). Although the fraction of all cryptosporidiosis
cases that are laboratory confirmed is unknown, during the 1993
Milwaukee outbreak, 739 cases from an estimated 403,000 cases total
were confirmed by a laboratory (MacKenzie et al., 1994). These data
indicate a ratio of 1 laboratory confirmed case per 545 people
estimated to be ill with cryptosporidiosis.
A few studies have attempted to determine exposure in certain areas
by measuring seroprevalence of Cryptosporidium antibodies (the
frequency at which antibodies are found in the blood). Detection of
such antibodies (seropositivity), however, does not mean that the
person actually experienced symptoms of cryptosporidiosis. An
individual can be asymptomatically infected and still excrete oocysts.
Seroprevalence, though, is still a method for estimating the exposure
to Cryptosporidium that has occurred within a limited time period (the
antibodies may last only a few months).
Frost et al. (2001) conducted a paired city study, in which the
serological response of blood donors in a city using ground water as
its water source was compared to that of donors in a city using surface
water as its source. Rates of seropositivity were higher (49 vs. 36
percent) in the city with the surface water source. A similar study in
two other cities (Frost et al. 2002) showed a seropositivity rate of 54
percent in the city served by surface water compared to 38 percent in
the city served by ground water. These studies suggest that drinking
water from surface sources may be a factor in the higher rates of
seropositivity.

D. Specific Concerns Following the IESWTR and LT1ESWTR

In the LT2ESWTR, EPA is addressing a number of public health
concerns that remain following implementation of the IESWTR and
LT1ESWTR. These are as follows:
? The need for filtered PWSs with higher levels of source
water Cryptosporidium contamination to provide additional risk-based
treatment for Cryptosporidium beyond IESWTR or LT1ESWTR requirements;
? The need for unfiltered PWSs to provide risk-based
treatment for Cryptosporidium to achieve equivalent public health
protection with filtered PWSs; and
? The need for PWSs with uncovered finished water storage
facilities to take steps to reduce the risk of contamination of treated
water prior to distribution to consumers.
EPA and stakeholders identified each of these issues as public
health concerns during development of the IESWTR (USEPA 1994, 1997).
However, the Agency was unable to address these concerns in those
regulations due to data gaps in the areas of health effects,
occurrence, analytical methods, and treatment. Consequently, EPA
followed a two-stage strategy for microbial and disinfection byproducts
rules. Under this strategy, the IESWTR and LT1ESWTR were promulgated to
provide an initial improvement in public health protection in large and
small PWSs, respectively, while additional data to support a more
comprehensive regulatory approach were collected.
Since promulgating the IESWTR and LT1ESWTR, EPA has worked with
stakeholders to collect and analyze significant new information to fill
data gaps related to Cryptosporidium risk management in PWSs. The next
section presents EPA's evaluation of these data and their implications
for both the risk of Cryptosporidium in filtered and unfiltered PWSs
and the feasibility of steps to limit this risk. In addition, the
Agency has evaluated additional data related to mitigating risks with
uncovered finished water storage facilities, which are presented in
section IV.F.

E. New Information on Cryptosporidium Risk Management

EPA and stakeholders determined during development of the IESWTR
that in order to establish risk-based treatment requirements for
Cryptosporidium, additional information was needed in the following
areas: (1) The risk associated with a given level of Cryptosporidium
(i.e., infectivity); (2) the occurrence of Cryptosporidium in PWS
sources; (3) analytical methods that would suffice for making site-
specific source water Cryptosporidium density estimates; and (4) the
use of treatment technologies to achieve specific levels of
Cryptosporidium disinfection (USEPA 1997).
In today's final LT2ESWTR, EPA is promulgating risk-based
Cryptosporidium treatment requirements for filtered and unfiltered
PWSs. The Agency believes that the critical data gaps in the areas of
infectivity, occurrence, analytical methods, and treatment that
prevented the adoption of such an approach under earlier regulations
have been addressed. The new information that the Agency and
stakeholders evaluated in each of these areas and its significance for
today's LT2ESWTR are summarized as follows. See section VI.L for a
summary of public comments on EPA's use of Cryptosporidium infectivity and

[[Page 662]]

occurrence data in assessing benefits of the LT2ESWTR.
1. Infectivity
Infectivity relates the probability of infection to the number of
Cryptosporidium oocysts that a person ingests. It is used to predict
the disease burden associated with a particular Cryptosporidium level
in drinking water. Information on Cryptosporidium infectivity comes
from dose-response studies where healthy human volunteers ingest
different numbers of oocysts (i.e., the ``dose'') and are subsequently
evaluated for signs of infection and illness (i.e., the ``response'').
Prior to the IESWTR, data from a human dose-response study of one
Cryptosporidium isolate (IOWA) had been published (DuPont et al. 1995).
Following IESWTR promulgation, a study of two additional isolates (TAMU
and UCP) was completed and published (Okhuysen et al. 1999). This 1999
study also reanalyzed the IOWA study results. The measured infectivity
of Cryptosporidium oocysts varied over a wide range in the Okhuysen et
al. (1999) study. The UCP oocysts were much less infective than the
IOWA oocysts, and the TAMU oocysts were much more infective.
EPA analyzed these new data for the proposed LT2ESWTR using two
different dose-response models. This analysis suggested that the
overall infectivity of Cryptosporidium is greater than was estimated
for the IESWTR (USEPA 2003a). Specifically, EPA estimated the mean
probability of infection from ingesting a single infectious oocyst
ranges from 7 to 10 percent. This infection rate is approximately 20
times higher than the estimate of 0.4 percent used in the IESWTR.
Since the publication of the proposed LT2ESWTR, EPA has evaluated
three additional studies of Cryptosporidium infectivity. EPA also
received a recommendation from the SAB that it analyze Cryptosporidium
infectivity data using a wider range of models. Accordingly, EPA re-
estimated Cryptosporidium infectivity using the new data and six
different dose-response models, including the two models used at
proposal. Estimates from the new data and models for the probability of
infection from ingesting a single infectious oocyst range from 4 to 16
percent. A detailed discussion of the models and their varying
assumptions is provided in the LT2ESWTR Economic Analysis (USEPA 2005a).
As is apparent from these results, substantial uncertainty about
the infectivity of Cryptosporidium remains in several areas. These
include the variability in host susceptibility, response at very low
oocyst doses typical of drinking water ingestion, and the relative
infectivity and occurrence of different Cryptosporidium isolates in the
environment. To address this uncertainty, EPA conducted its health risk
reduction and benefits analyses using a representative range of model
results. In the summary tables for these analyses, three sets of
estimates are presented: A ``high'' estimate based on the model that
showed the highest mean baseline risk; a ``medium'' estimate, based on
the models and data used at proposal, which also happens to be in the
middle of the range of estimates produced by the six models using the
newly available data; and a ``low'' estimate, based on the model that
showed the lowest mean baseline risk.
These estimates should not be construed as upper and lower bounds
on illnesses avoided and benefits. For each model, a distribution of
effects is estimated, and the ``high'' and ``low'' estimates show only
the means of these distributions for two different model choices. The
detailed distribution of effects is presented for the proposal model in
the Economic Analysis (USEPA 2005a). Further, the six dose-response
models used in this analysis do not cover all possible variations of
models that might have been used with the data, and it is possible that
estimates with other models would fall outside the range presented.
However, as discussed in the Economic Analysis, EPA believes that the
models used in the analyses reflect a reasonable range of results based
on important dimensions of model choice.
Regardless of which model is chosen, the available infectivity data
suggest that the risk associated with a given concentration of
Cryptosporidium is most likely higher than EPA had estimated for the
IESWTR. This finding supports the need for increased treatment for
Cryptosporidium as required under the LT2ESWTR.
2. Occurrence
Information on the occurrence of Cryptosporidium oocysts in
drinking water sources is a critical parameter for assessing risk and
the need for additional treatment for this pathogen. For the IESWTR,
EPA had no national survey data on Cryptosporidium occurrence and
relied instead on several studies that were local or regional. After
promulgating the IESWTR, EPA obtained data from two national surveys,
the Information Collection Rule (ICR) and the ICR Supplemental Surveys
(ICRSS), which were designed to provide improved estimates of
occurrence on a national basis.
The ICR included monthly sampling for Cryptosporidium and other
water quality parameters from the sources of approximately 350 large
PWSs over 18 months. The ICRSS involved twice-per-month Cryptosporidium
sampling from the sources of a statistically random sample of 40 large
and 40 medium PWSs over 12 months. In addition, the ICRSS required the
use of an improved analytical method for Cryptosporidium analysis that
had a higher method recovery (the likelihood that an oocyst present in
the sample will be counted) and enhanced sample preparation procedures.
EPA analyzed ICR and ICRSS data using a statistical model to
account for factors like method recovery and sample volume analyzed. As
described in more detail in EPA's Occurrence and Exposure Assessment
for the LT2ESWTR (USEPA 2005b), the ICR and ICRSS results demonstrate
two main differences for filtered PWSs in comparison to Cryptosporidium
occurrence data used for the IESWTR:

(1) The occurrence of Cryptosporidium in many drinking water
sources is lower than was indicated by the data used in IESWTR. For
example, median Cryptosporidium levels for the ICR and ICRSS data
are approximately 0.05/L, which is nearly 50 times lower than the
median IESWTR estimates of 2.3 oocysts/L (USEPA 1998a).
(2) Cryptosporidium occurrence is more variable from location to
location than was shown by the data considered for the IESWTR. This
finding demonstrates that, although median occurrence levels are
below those estimated for the IESWTR, a subset of PWSs contains
Cryptosporidium levels that are considerably greater than the median.

These results, therefore, indicate that Cryptosporidium levels are
relatively low in most water sources, but a subset of sources with
relatively higher concentrations may require additional treatment.
These findings support a risk-targeted approach for the LT2ESWTR
wherein additional Cryptosporidium treatment is required only for
filtered PWSs with the highest source water pathogen levels.
Only the ICR provided data to evaluate Cryptosporidium occurrence
in unfiltered PWS sources. The median Cryptosporidium level among
unfiltered PWS sources was 0.0079 oocysts/L. This level is approximately
10 times lower than the median level for filtered PWS sources.
When the Cryptosporidium removal that filtered PWSs achieve is
taken into account, these occurrence data suggest that unfiltered PWSs
typically have

[[Page 663]]

higher concentrations of Cryptosporidium in their treated water than
filtered PWSs. EPA has estimated that on average, conventional
filtration plants remove around 99.9 percent (3-log) of the
Cryptosporidium present in the source water. Most unfiltered PWSs,
however, provide no treatment for Cryptosporidium. If an unfiltered PWS
had a source water Cryptosporidium level 10 times lower than a filtered
PWS and the filtered PWS achieved 3-log Cryptosporidium removal, then
the Cryptosporidium level in the treated water of the unfiltered PWS
would be 100 times higher than in the filtered PWS.
These results suggest that to achieve public health protection
equivalent to that provided by filtered PWSs, unfiltered PWSs must take
additional steps. Thus, this finding supports the need for Cryptosporidium
treatment requirements for unfiltered PWSs under the LT2ESWTR.
3. Analytical Methods
To establish risk-targeted treatment requirements, analytical
methods must be available to estimate the contaminant densities in PWS
sources. These density estimates are used to determine the level of
treatment that is needed at a particular site.
When EPA developed the IESWTR, the best available method for
measuring Cryptosporidium was the Information Collection Rule Protozoan
Method (ICR Method). The ICR Method provided a quantitative measurement
of Cryptosporidium oocysts, but typically undercounted the actual
occurrence due to low method recovery. For example, in a spiking study
(studies in which known quantities of oocysts are added to water
samples) conducted during the ICR survey, the mean recovery of spiked
Cryptosporidium oocysts was only 12 percent (Scheller et al. 2002). EPA
concluded that the ICR Method was adequate for making national
occurrence estimates in the ICR survey but would not suffice for making
estimates of Cryptosporidium levels at specific sites.
Subsequent to promulgating the IESWTR, EPA developed an improved
Cryptosporidium method, EPA Method 1622 (and later, 1623), to achieve
higher recovery rates and lower inter- and intra-laboratory variability
than previous methods. Methods 1622 and 1623 incorporate improvements
in the concentration, separation, staining, and microscope examination
procedures. During the ICRSS, which required the use of Method 1622 or
1623, a spiking study demonstrated a mean Cryptosporidium recovery of
43 percent (Connell et al. 2000). Thus, mean Cryptosporidium recovery
with Methods 1622 and 1623 was more than 3.5 times higher compared to
the ICR Method performance in the earlier spiking study. In addition,
the relative variation in recovery from sample to sample was lower with
Methods 1622 and 1623.
As described in section IV of this preamble, EPA has concluded that
a monitoring program using Methods 1622 or 1623 can be effective in
characterizing PWSs source water Cryptosporidium levels for purposes of
determining the need for additional treatment requirements. This
finding supports the feasibility of risk-targeted treatment
requirements under the LT2ESWTR.
4. Treatment
To establish risk-targeted Cryptosporidium treatment requirements,
feasible treatment processes must be available that allow PWSs to
inactivate or remove Cryptosporidium. PWSs may then implement these
treatment processes to comply with additional treatment requirements.
During development of the IESWTR, EPA recognized that chlorine, the
most commonly used disinfectant, is ineffective for inactivating
Cryptosporidium. Studies suggested that other disinfectants like ozone
and chlorine dioxide could be effective against Cryptosporidium.
However, EPA concluded that data available at that time were not
sufficient to define how any disinfectant could be applied to achieve a
specific level of Cryptosporidium inactivation (USEPA 1997). This
conclusion was due in part to methodological inconsistencies and
shortcomings in the available studies.
With the completion of major studies since promulgation of the
IESWTR, EPA has acquired the data necessary to establish standards for
Cryptosporidium inactivation by several disinfectants. For ozone and
chlorine dioxide, EPA reviewed new studies by Rennecker et al. (1999),
Owens et al. (1999, 2000), Oppenheimer et al. (2000), Ruffell et al.
(2000), and Li et al. (2001). Collectively, these studies cover a wide
range of both natural and laboratory water conditions. Based on these
studies, EPA has developed tables that specify the product of ozone or
chlorine dioxide concentration and time of exposure (i.e., CT tables)
needed to achieve up to 3-log Cryptosporidium inactivation. Section
IV.D of this preamble shows these tables.
Most significantly, many recent studies have demonstrated that UV
light is efficient for inactivating high levels of Cryptosporidium.
These studies include Clancy et al. (1998, 2000, 2002), Bukhari et al.
(1999), Craik et al. (2000, 2001), Landis et al. 2000), Sommer et al.
(2001), Shin et al. (2001), and Oppenheimer et al. (2002). Using
results from these studies, EPA has defined the UV light intensity and
exposure time required for up to 4-log Cryptosporidium inactivation.
Section IV.D presents these values. EPA has determined that UV light is
a feasible technology for PWSs of all sizes to inactivate Cryptosporidium.
EPA has also developed standards for processes that physically
remove Cryptosporidium contamination. These processes include river
bank filtration, sedimentation basins, bag filters, cartridge filters,
and membranes. Section IV.D presents design and operational standards
for these processes, along with a summary of supporting studies.
The development of these standards for Cryptosporidium inactivation
and removal processes overcomes a significant limitation that existed
when EPA developed the IESWTR. These standards will allow PWSs to
implement cost-effective strategies to comply with additional
Cryptosporidium treatment requirements under the LT2ESWTR.

F. Federal Advisory Committee Recommendations

EPA convened the Stage 2 M-DBP Federal Advisory Committee in March
1999 to evaluate new information and develop recommendations for the
LT2ESWTR and Stage 2 DBPR. The Committee was comprised of
representatives from EPA, State and local public health and regulatory
agencies, local elected officials, Indian Tribes, drinking water
suppliers, chemical and equipment manufacturers, and public interest
groups. A technical workgroup provided analytical support for the
Committee's discussions.
Committee members signed an Agreement in Principle in September
2000 stating consensus recommendations of the group. The Agreement was
published in a December 29, 2000 Federal Register notice (USEPA 2000a).
For the LT2ESWTR, the consensus recommendations of the Committee are
summarized as follows:
(1) Supplemental risk-targeted Cryptosporidium treatment by
filtered PWSs with higher source water contaminant levels as shown by
monitoring results;
(2) Cryptosporidium inactivation by all unfiltered PWSs, which must
meet

[[Page 664]]

overall treatment requirements using a minimum of 2 disinfectants;
(3) A ``toolbox'' of treatment and control processes for PWSs to
comply with Cryptosporidium treatment requirements;
(4) Reduced monitoring burden for small filtered PWSs;
(5) Future monitoring to confirm or revise source water quality
assessments;
(6) Development of guidance for UV disinfection and other toolbox
components; and
(7) Cover or treat existing uncovered finished water reservoirs
(i.e., storage facilities) or implement risk mitigation plans.
These recommendations reflect a Committee judgement that, based on
available information, additional risk-based Cryptosporidium treatment
requirements for filtered and unfiltered PWSs are appropriate and
feasible under the LT2ESWTR. Much of today's final LT2ESWTR reflects
the Committee's recommendations. The next part of this preamble
describes specific requirements of the rule.

IV. Explanation of Today's Action

A. Source Water Monitoring Requirements

Today's rule requires PWSs using surface water or GWUDI sources to
monitor their source water to assess the level of Cryptosporidium.
Monitoring results assign a PWS to a Cryptosporidium treatment bin,
which determines the extent of additional Cryptosporidium treatment
requirements (sections IV.B and IV.C described treatment requirements
for filtered and unfiltered PWSs, respectively).
Source water monitoring under the LT2ESWTR is designed to ascertain
the mean level of Cryptosporidium in the influent to a surface water
treatment plant. Requirements differ by PWS size (above or below 10,000
people served) and treatment plant type (filtered or unfiltered PWS).
This section describes monitoring requirements for sampling parameters
and frequency, sampling location, sampling schedule, monitoring plants
that operate only part of the year, failing to monitor, providing
treatment instead of monitoring, grandfathering previously collected
data, ongoing watershed assessment, second round of monitoring, and new
source monitoring.
Other sections of this preamble describe additional requirements
related to monitoring, including compliance schedules (section IV.G),
reporting of monitoring results (section IV.I), use of approved
analytical methods, including minimum sample volume (section IV.J), and
use of approved laboratories (section IV.K). As described in section
IV.G, monitoring compliance dates under the LT2ESWTR are staggered:
smaller PWSs begin monitoring after larger PWSs.
For additional information, see Source Water Monitoring Guidance
Manual for Public Water Systems under the Long Term 2 Enhanced Surface
Water Treatment Rule. This document provides guidance on sampling
location, procedures for collecting and shipping samples, contracting
with laboratories, and related topics to assist PWSs in complying with
LT2ESWTR monitoring requirements. It may be acquired from EPA's Safe
Drinking Water Hotline, which can be contacted as described under FOR
FURTHER INFORMATION CONTACT at the beginning of this document.
1. Today's Rule
a. Sampling parameters and frequency. Requirements for the source
water parameters that PWSs must measure under the LT2ESWTR, as well as
the sampling frequency and duration, are stated as follows for large
and small PWSs, including both filtered and unfiltered plants:

Large Filtered PWSs

Filtered PWSs serving at least 10,000 people must sample at least
monthly for Cryptosporidium, E. coli, and turbidity for a period of two
years. Sampling may be conducted at a higher frequency (e.g., twice-
per-month, once-per-week) but the sampling must be evenly spaced
throughout the monitoring period. As described in section IV.B,
filtered PWSs that sample at least twice-per-month over two years use a
different calculation, which is less conservative, to determine their
treatment bin classification under the LT2ESWTR.

Large Unfiltered PWSs

Unfiltered PWSs serving at least 10,000 people must also sample for
Cryptosporidium at least monthly for a period of 2 years. No E. coli or
turbidity monitoring is required for unfiltered PWSs. Unfiltered PWSs
may choose to sample more frequently; however, as described in section
IV.C, a higher sampling frequency does not change the calculation used
to determine unfiltered PWS Cryptosporidium treatment requirements.

Small Filtered PWSs

Filtered PWSs serving fewer than 10,000 people (i.e., small PWSs)
monitor under the LT2ESWTR using a two-phase strategy that begins with
an indicator screening analysis. Small filtered PWSs must initially
sample for E. coli at least once every two weeks for a period of one
year. Cryptosporidium monitoring is required of these PWSs only if the
indicator monitoring results meet one of the following conditions:
(1) For PWSs using lake/reservoir sources, the annual mean E. coli
concentration is greater than 10 E. coli/100 mL.
(2) For PWSs using flowing stream sources, the annual mean E. coli
concentration is greater than 50 E. coli/100 mL.
PWSs using ground water under the direct influence of surface water
must comply with the requirement to monitor for Cryptosporidium based
on the E. coli level that applies to the nearest surface water body. If
no surface water body is nearby, the PWS must comply based on the
requirements that apply to PWSs using lake/reservoir sources.
The State may approve small filtered PWSs to monitor for an
indicator other than E. coli. The State also may approve an alternative
E. coli concentration to trigger Cryptosporidium monitoring. This
approval must be in writing and must be based on a State determination
that the alternative indicator and/or trigger level will more
accurately identify whether a PWS will exceed the Bin 1 Cryptosporidium
level of 0.075 oocysts/L, as stated in section IV.B.1 of this preamble.
EPA will issue guidance to States on alternative indicators and trigger
levels, if warranted, based on large PWS monitoring results.
Small filtered PWSs may elect to skip E. coli monitoring if they
notify the State that they will monitor for Cryptosporidium. PWSs must
notify the State no later than three months prior to the date the PWS
is required to begin monitoring (see section IV.G for specific dates).
Small filtered PWSs that are required to monitor for
Cryptosporidium must conduct this monitoring using either of two
frequencies: (1) Sample at least twice-per-month for a period of one
year or (2) sample at least once-per-month for a period of two years.
Note that the same treatment compliance dates apply to the PWS
regardless of which Cryptosporidium sampling frequency is used (i.e.,
selecting the two-year Cryptosporidium sampling frequency does not
extend Cryptosporidium treatment compliance deadlines).

Small Unfiltered PWSs

All unfiltered PWSs serving fewer than 10,000 people must monitor
for Cryptosporidium. The E. coli screening analysis used by small
filtered PWSs is not applicable to small unfiltered PWSs. Small
unfiltered PWSs must use either

[[Page 665]]

of the same two Cryptosporidium sampling frequencies available to small
filtered PWSs: (1) Sample twice-per-month for one year or (2) sample
once-per-month for two years. As with small filtered PWSs, the same
treatment compliance dates apply to the PWS regardless of which
Cryptosporidium sampling frequency is used.
b. Sampling location. PWSs must collect source water samples for
each plant that treats a surface water or GWUDI source. However, where
multiple plants receive all of their water from the same influent, such
as plants that draw water from the same intake or pipe, the State may
approve one set of monitoring results to be applied to all plants.
PWSs must collect source water samples prior to chemical treatment,
such as coagulants, oxidants, and disinfectants, unless the following
condition is met: The State may approve a system to collect a sample
after chemical treatment if the State determines that collecting a
sample prior to chemical treatment is not feasible and that the
chemical treatment is unlikely to have a significant adverse effect on
the analysis of the sample. PWSs that recycle filter backwash must
collect samples prior to the point of filter backwash addition due to
the likely presence of coagulant and other treatment chemicals in the
backwash. See section IV.D.6 for directions on sampling location for
PWSs using bank filtration.
For plants that use multiple water sources at the same time, PWSs
must collect samples from a tap where the sources are combined prior to
treatment, if available. If a blended source tap is not available, PWSs
must collect samples from each source and either analyze a weighted
composite (blended) sample or analyze samples from each source
separately and determine a weighted average of the results. The
weighting of sources must reflect the relative usage of the different
sources by the treatment plant at the time the sample is collected.
PWSs must submit a description of their proposed sampling
location(s) to the State no later than three months prior to the date
the PWS must begin monitoring (see section IV.G for specific dates).
This description must address the position of the sampling location in
relation to the PWS's water source(s) and treatment processes,
including points of chemical addition and filter backwash recycle. If
the State does not respond to a PWS regarding sampling location(s), the
PWS must begin sampling at the reported location. See Source Water
Monitoring Guidance Manual for Public Water Systems under the Long Term
2 Enhanced Surface Water Treatment Rule, which can be acquired as
stated previously, for guidance on sampling location descriptions.
c. Sampling schedule. PWSs must collect samples in accordance with
a schedule that the PWS develops and reports prior to initiating
monitoring. The sampling schedule must specify the calendar dates when
the PWS will collect each required sample in a particular round of
monitoring. Scheduled sampling dates must be evenly distributed
throughout the monitoring period, but may be arranged to accommodate
holidays, weekends, and other events when collecting or analyzing a
sample would be problematic (e.g., a PWS is not required to schedule
samples on the same calendar date each month).
PWSs must submit sampling schedules no later than three months
prior to the date the PWS must begin a round of monitoring (see section
IV.G for specific dates). Unless the State approves an alternative
procedure, large PWSs (serving at least 10,000 people) must report
their sampling schedule for initial source water monitoring to EPA
using the LT2ESWTR electronic data reporting and review system
described in section IV.I. Schedules for initial monitoring by small
PWSs and for the second round of monitoring by all PWSs must be
reported to the State. PWSs should verify that their laboratory can
accommodate the scheduled sampling dates before submitting the schedule.
EPA will not formally approve sampling schedules but will notify a
PWS if its sampling schedules does not meet the requirements of today's
rule (e.g., does not include the required number of samples). If a PWS
does not receive notification from the State or EPA regarding the
sampling schedule, the PWS must begin monitoring according to the
reported sampling schedule.
PWSs must collect samples within two days before or two days after
the dates indicated in their sampling schedules (i.e., within a 5-day
period around the schedule date) unless one of the following two
conditions applies:
(1) If an extreme condition or situation exists that may pose
danger to the sample collector, or that cannot be avoided and causes
the PWS to be unable to sample in the scheduled 5-day period, the PWS
must sample as close to the scheduled date as is feasible unless the
State approves an alternative sampling date. The PWS must submit an
explanation for the delayed sampling date to the State concurrent with
the shipment of the samples to the laboratory.
(2) If a PWS is unable to report a valid analytical result for a
scheduled sampling date due to equipment failure, loss of or damage to
the sample, failure to comply with the analytical method requirements,
or the failure of an approved laboratory to analyze the sample, then
the PWS must collect a replacement sample. Collection of the
replacement sample must occur within 21 days of the PWS receiving
information that an analytical result cannot be reported for the
scheduled date unless the PWS demonstrates that collecting a
replacement sample within this time frame is not feasible or the State
approves an alternative resampling date. The PWS must submit an
explanation for the resampling date to the State concurrent with the
shipment of the sample to the laboratory.
Failure to collect a required sample within the 5-day period around
a scheduled date that does not meet one of these two conditions is a
monitoring violation. PWSs must revise their sampling schedules to add
dates for collecting all missed samples and must submit the revised
schedule to the State for approval prior to when the PWS begins
collecting the missed samples.
d. Plants operating only part of the year. Some PWSs operate
surface water treatment plants for only part of the year. This includes
PWSs that provide water for only a fraction of the year (e.g., resorts
open only in the summer) and PWSs that use a surface water plant to
supplement another source only during periods of high demand.
Most LT2ESWTR monitoring, treatment, and implementation schedule
requirements apply to such plants. Monitoring requirements, however,
differ in two respects:
(1) PWSs must conduct sampling only during months of the 2 year
monitoring period when the plant operates unless the State specifies
another monitoring period based on plant operating practices; and
(2) For plants that operate less than six months per year and where
Cryptosporidium monitoring is required, PWSs must collect at least six
Cryptosporidium samples per year during each of two years of monitoring.
e. Failing to monitor. Today's rule requires PWSs to provide a Tier
3 public notice for violation of monitoring and testing procedure
requirements, including the failure to collect one or two source water
Cryptosporidium samples. If a PWS fails to collect three or more
Cryptosporidium samples, other than in specifically exempted situations
(see section IV.A.1.c), the PWS must

[[Page 666]]

provide a Tier 2 special public notice. Violations for failing to
monitor persist until the State determines that the PWS has begun
sampling on a revised schedule that includes dates for the collection
of missed samples. Section IV.H provides further details on public
notice requirements of the LT2ESWTR.
PWSs must report their bin classification (or mean Cryptosporidium
level for unfiltered PWSs) no later than six months after the end of
the scheduled monitoring period (specific dates in section IV.G).
Failure by a PWS to collect the required number of Cryptosporidium
samples to report its bin classification or mean Cryptosporidium level
by the compliance date is a treatment technique violation and the PWS
must provide a Tier 2 special public notice (unless the PWS has already
provided a Tier 2 public notice for missing three sampling dates and is
successfully meeting a State-approved schedule for sampling). The
treatment technique violation and public notice requirements persist
until the State determines that the PWS is implementing a State-
approved monitoring plan to allow bin classification or will install
the highest level of treatment required under the rule, as described next.
f. Providing treatment instead of monitoring. PWSs are not required
to conduct source water monitoring under the LT2ESWTR for plants that
will provide the highest level of treatment required under the rule.
This applies both to plants that provide this level of treatment at the
time the plant would otherwise begin source water monitoring and to
plants that commit to install technology to achieve this level of
treatment by the applicable compliance date for meeting Cryptosporidium
treatment requirements under the LT2ESWTR.
Filtered PWSs are not required to monitor at plants that will
provide a total of at least 5.5-log of treatment for Cryptosporidium,
equivalent to meeting the treatment requirements of Bin 4 as discussed
in section IV.B. Unfiltered PWSs are not required to monitor for plants
that will provide a total of at least 3-log of Cryptosporidium
inactivation, equivalent to meeting the treatment requirements for
unfiltered PWSs with source water Cryptosporidium levels above 0.01
oocysts/L as discussed in section IV.C.
PWSs that intend to provide this level of treatment rather than
initiate monitoring must notify the State no later than three months
prior to the month the PWS must otherwise begin monitoring. PWSs submit
this notification in lieu of submitting a sampling schedule. In
addition, a PWS may choose to stop sampling at any point after it has
initiated monitoring if it notifies the State that it will provide the
highest level of treatment. In both cases, the PWSs must install and
operate technologies to achieve this level of treatment no later than
the applicable Cryptosporidium treatment compliance date for the PWS as
specified in section IV.G. Failure to provide this treatment by the
compliance date is a treatment technique violation.
g. Grandfathering previously collected data. If the State approves,
PWSs may comply with the initial source water monitoring requirements
of today's rule by using (i.e., grandfathering) sample results
collected before the PWS is required to begin monitoring. PWSs may
grandfather monitoring results either in lieu of or in addition to
conducting new monitoring under the rule. To be eligible for
grandfathering, monitoring results must be equivalent in data quality
to monitoring PWSs conduct under today's rule and the PWS must comply
with reporting requirements. Details of these requirements follow.

Grandfathered Data Quality Requirements

? Analysis of E. coli samples must meet the analytical
method and approved laboratory requirements for source water monitoring
under today's rule. PWSs are not required to report E. coli and
turbidity data in order to grandfather Cryptosporidium monitoring
results, although EPA requests that PWSs report these data if they are
available. PWSs that grandfather Cryptosporidium data without
associated E. coli and turbidity data are not required to conduct
separate monitoring for these parameters when they have satisfied
Cryptosporidium monitoring requirements.
? Analysis of Cryptosporidium samples must meet the criteria
of a validated version of EPA Method 1622 or 1623, which are described
in USEPA 1999a, USEPA 1999b, USEPA 2001e, USEPA 2001f, USEPA 2005c, and
USEPA 2005d. The volume analyzed for each sample must meet the criteria
described in section IV.J, which are at least 10 L of sample or at
least 2 mL of packet pellet volume or as much volume as two approved
filters can accommodate before clogging.
? The sampling location must meet the criteria for LT2ESWTR
monitoring, as described previously.
? For Cryptosporidium samples, the sampling frequency must
be at least monthly and on a regular schedule. The collection of
individual samples may deviate from a regular schedule under the same
criteria that apply to deviation from LT2ESWTR sampling schedules, as
described previously. Additionally, deviations in the sampling
frequency of previously collected data are allowed under the following
conditions: (1) PWSs may grandfather data where there are gaps in the
sampling frequency if the State approves and if the PWS conducts
additional monitoring when specified by the State to ensure the data
used for bin classification are seasonally representative and unbiased;
and (2) PWSs may grandfather data where the sampling frequency varies
(e.g., one year of sampling monthly and one year of sampling twice-per-
month); monthly average sample concentrations must be used to calculate
the bin classification, as described in section IV.B.

Grandfathered Data Reporting Requirements

PWSs that request to grandfather previously collected monitoring
results must report the following information by the applicable dates
listed in this section. PWSs serving at least 10,000 people must report
this information to EPA unless the State approves an alternate
procedure for reporting. PWSs serving fewer than 10,000 people must
report this information to the State.
PWSs must report that they intend to submit previously collected
monitoring results for grandfathering. This report must specify the
number of previously collected results the PWS will submit, the dates
of the first and last sample, and whether a PWS will conduct additional
source water monitoring for initial bin classification. PWSs must
report this information no later than three months prior to the date
the PWSs is required to start monitoring, as shown in section IV.G.
PWSs must report previously collected monitoring results for
grandfathering, along with the required documentation listed in this
section, no later than two months after the month the PWS is required
to start monitoring, as shown in section IV.G.
? For each sample Cryptosporidium or E. coli result, PWSs
must report the applicable data elements in section IV.I.1.
? PWSs must certify to EPA or the State that the reported
monitoring results include all results the PWS generated during the
time period beginning with the first reported result and ending with
the final reported result. This applies to samples that were collected
from the sampling location specified for source water monitoring

[[Page 667]]

under this subpart, not spiked, and analyzed using the laboratory's
routine process for the analytical methods listed in this section.
? PWSs must certify to EPA or the State that the samples
were representative of a plant's source water(s) and the source
water(s) have not changed. PWSs must submit to EPA a description of the
sampling location(s) for each water treatment plant, which must address
the position of the sampling location in relation to the PWS's water
source(s) and treatment processes, including points of chemical
addition and filter backwash recycle.
? For Cryptosporidium samples, the laboratory or
laboratories that analyzed the samples must provide a letter certifying
that the quality control criteria specified in the methods listed in
this section were met for each sample batch associated with the
reported results. Alternatively, the laboratory may provide bench
sheets and sample examination report forms for each field, matrix
spike, initial precision and recovery (IPR), ongoing precision and
recovery (OPR), and method blank sample associated with the reported
results.
? If the State determines that a previously collected data
set submitted for grandfathering was generated during source water
conditions that were not normal for the PWS, such as a drought, the
State may disapprove the data. Alternatively, the State may approve the
previously collected data if the PWS reports additional source water
monitoring data, as determined by the State, to ensure that the overall
data set used for bin classification represents average source water
conditions for the PWS.
If a PWS submits previously collected data that fully meet the
number of samples required for initial source water monitoring and some
of the data are rejected due to not meeting the requirements of this
section, PWSs must conduct additional monitoring to replace rejected
data on a schedule the State approves. PWSs are not required to begin
this additional monitoring until at least two months after notification
that data have been rejected and additional monitoring is necessary.
h. Ongoing watershed assessment. Today's rule includes provisions
to assess changes in a PWS's source water quality following initial bin
classification. As required by 40 CFR 142.16(b)(3)(i), source water is
one of the components that States must address during the sanitary
surveys that are required for surface water PWSs. These sanitary
surveys must be conducted every 3 years for community PWSs and every 5
years for non-community PWSs. Under today's rule, if the State
determines during the sanitary survey or an equivalent source water
assessment that significant changes have occurred in the watershed that
could lead to increased contamination of the source water by
Cryptosporidium, the PWS must take actions specified by the State to
address the contamination. These actions may include additional source
water monitoring and/or implementing options from the microbial toolbox
discussed in section IV.D.
i. Second round of monitoring. PWSs must begin a second round of
source water monitoring beginning six years after initial bin
classification (see compliance dates in section IV.G). If EPA does not
modify LT2ESWTR requirements by issuing a new regulation prior to the
second round of monitoring, PWSs must carry out this monitoring
according to the requirements that apply to the initial round of source
water monitoring. PWSs will then be reclassified in LT2ESWTR treatment
bins based on the second-round monitoring result. However, if EPA
changes the LT2ESWTR treatment bin structure to reflect a new
analytical method or new risk information, PWSs will undergo a risk
characterization in accordance with the revised rule.
j. New source monitoring. A PWS that begins using a new surface
water source after the date the PWS is required to conduct source water
monitoring under the LT2ESWTR must monitor the new source on a schedule
approved by the State. This applies to both new plants that begin
operation and previously operating plants that bring a new source on-
line after the required monitoring date for the PWS. The State may
determine that monitoring should be conducted before a new plant or
source is brought on-line or initiated within some time period
afterward. The new source monitoring must meet all LT2ESWTR
requirements as specified previously in this section. The PWS must also
determine its treatment bin classification and comply with any
additional Cryptosporidium treatment requirements based on the
monitoring results on a schedule approved by the State.
2. Background and Analysis
Monitoring requirements in today's rule are designed to ascertain
Cryptosporidium levels with suitable accuracy for making treatment bin
classifications and in a time frame that does not delay the
installation of Cryptosporidium treatment where needed. The following
discussion summarizes the basis for monitoring requirements with
respect to sampling parameters and frequency, sampling location,
sampling schedule, monitoring plants that operate for only part of the
year, failing to monitor, grandfathering previously collected data,
ongoing watershed assessment, and the second round of monitoring. Most
of these requirements were part of the August 11, 2003, proposal for
today's final rule, and supporting analyses are presented in greater
detail in the proposal (USEPA 2003a). Differences from proposed
requirements are noted in the following discussion where applicable.
a. Sampling parameters and frequency. The requirements in today's
final rule for the parameters and frequency of source water monitoring
are unchanged from those in the proposed rule (USEPA 2003a), with the
exception of an additional option for lower frequency Cryptosporidium
sampling by small PWSs. These requirements reflect recommendations by
the Stage 2 M-DBP Advisory Committee. They are designed to ensure a low
potential for misclassification in assigning PWSs to Cryptosporidium
treatment bins. The supporting analyses are summarized as follows for
Cryptosporidium and indicator (E. coli) monitoring:

Cryptosporidium Monitoring

EPA analyzed bin misclassification rates for different
Cryptosporidium monitoring programs by evaluating the likelihood of two
types of errors:
(1) A PWS with a true mean Cryptosporidium concentration of 0.5-log
(i.e., factor of 3.2) above a bin boundary is incorrectly assigned to a
lower bin (false negative) and
(2) A PWS with a true mean concentration of 0.5-log below a bin
boundary is incorrectly assigned to a higher bin (false positive).
The first type of error, a false negative, could lead to PWSs not
providing an adequate level of treatment while the second type of
error, a false positive, could lead to PWSs incurring additional costs
for unnecessary treatment.
EPA evaluated false positive and false negative rates for
monitoring programs that differed based on the number of samples
collected and the calculation used to determine the bin classification.
The analysis accounted for the sample volume assayed, variation in
source water Cryptosporidium occurrence, variation in analytical method
recovery, and other factors.
Results of this analysis indicate that PWSs must collect at least
24 samples in order to keep the likelihood of both false positives and
false negatives at five

[[Page 668]]

percent or less. Under a monitoring program involving fewer samples,
such as eight or twelve, a very conservative calculation for bin
classification would be required to achieve a low false negative rate
(e.g., bin classification based on the maximum or second highest sample
concentration). However, such an approach would result in false
positive rates in the range of 50 to 70 percent. Conversely, collecting
more than 24 samples can further reduce false positive and false
negative rates, albeit to a small degree. See the proposed LT2ESWTR for
additional details on this analysis (USEPA 2003a).
Based on the results of this analysis, EPA concluded that PWSs
operating year-round should collect at least 24 samples when they
monitor for Cryptosporidium. This number of samples ensures a high
likelihood of appropriate bin classification. Today's rule does not
allow bin classification based on fewer samples (except in the case of
PWSs operating only part of the year) as this would involve
unacceptably high false positive or false negative rates and would,
therefore, be an inappropriate basis to determine Cryptosporidium
treatment requirements. EPA believes, though, that PWSs should have the
choice to collect more than 24 samples to further improve the accuracy
of bin classification, and today's rule allows this.
In regard to the time frame for LT2ESWTR monitoring, the Agency
considered the trade-off between monitoring over a long period to
better capture temporal fluctuations and the desire to prescribe
additional treatment quickly to PWSs with higher Cryptosporidium
levels. Today's rule requires large PWSs to evaluate their source water
Cryptosporidium levels using two years of monitoring. This will account
for some degree of yearly variability, without significantly delaying
additional public health protection where needed.
Because many small PWSs will monitor for E. coli for one year
before monitoring for Cryptosporidium, today's rule allows two options.
Small PWSs can collect 24 Cryptosporidium samples over just one year
(resulting in a total of two years of source water monitoring when E.
coli monitoring is considered) or they can spread their 24
Cryptosporidium samples over two years. Spreading the Cryptosporidium
monitoring over two years will reduce the monitoring costs a PWS incurs
in a single year but will not push back the treatment compliance
deadline. This allowance for small PWSs to monitor for Cryptosporidium
over two years is a change from the proposal (USEPA 2003a). It stems
from recognition of the benefit this approach will provide to some
small PWSs in budgeting for monitoring.

Indicator Monitoring

Due to the relatively high cost of analyzing samples for
Cryptosporidium, the Advisory Committee and EPA investigated indicators
that are less costly to analyze to determine if any could be used in
place of Cryptosporidium monitoring. No indicators were identified that
correlated strongly with Cryptosporidium and could fully substitute for
Cryptosporidium monitoring for determining treatment bin
classifications. However, this investigation did identify an indicator,
E. coli, that can be used to identify some of the water sources that
are unlikely to exceed a Cryptosporidium level of 0.075 oocysts/L--the
level at which filtered PWSs must provide additional treatment under
the LT2ESWTR.
Data from the ICR and ICRSS were used in the investigation of
indicators. With these data, E. coli performed the best in identifying
sources with low Cryptosporidium levels. In addition, analyzing plants
separately based on source water type was necessary due to a different
relationship between E. coli and Cryptosporidium in reservoir/lake
sources compared to flowing stream sources.
The analysis of E. coli concentrations that could trigger
Cryptosporidium monitoring was based on false negative and false
positive rates. For this indicator, false negatives occur when sources
do not exceed the E. coli trigger value but exceed a Cryptosporidium
level of 0.075 oocysts/L. False positives occur when sources exceed the
E. coli trigger value but do not exceed a Cryptosporidium level of
0.075 oocysts/L. The false negative rate is critical because it
characterizes the ability of the indicator to identify those plants
with higher Cryptosporidium levels that should conduct Cryptosporidium
monitoring to determine if additional treatment is needed.
For plants with flowing stream sources, a mean E. coli trigger
concentration of 50/100 mL produced zero false negatives for both ICR
and ICRSS data sets. This means that in these data sets, all plants
that exceeded mean Cryptosporidium concentrations of 0.075 oocysts/L
also exceeded the E. coli trigger concentration. The false positive
rate for this trigger concentration was near 50 percent, meaning it was
not highly specific in targeting only those plants with high
Cryptosporidium levels. However, at a higher E. coli trigger
concentration, such as 100/100 mL, the false negative rate increased
without a significant reduction in the false positive rate.
For plants with lake or reservoir sources, a mean E. coli trigger
of 10/100 mL resulted in a false negative rate of 20 percent with ICR
data and 67 percent with ICRSS data. While this false negative rate in
the ICRSS data set appears high, it is based on just three plants in
this survey that used a reservoir/lake source and had a mean
Cryptosporidium level above 0.075 oocysts/L. With a lower E. coli
trigger concentration, such as 5/100 mL, the number of false negatives
in both data sets decreased by one plant, but the false positive rate
increased from 20 to 40 percent.
After evaluating these results, the Advisory Committee recommended
that all large PWSs monitor for Cryptosporidium, rather than using E.
coli in a screening analysis. EPA concurred with this recommendation
because it achieves the highest certainty that these PWSs will be
classified in the correct Cryptosporidium treatment bin and provide the
appropriate level of public health protection. In addition, the
Advisory Committee recommended and today's rule requires that large
filtered PWSs collect E. coli and turbidity samples along with
Cryptosporidium. EPA will use these data to confirm or, if necessary,
further refine the use of E. coli and possibly turbidity as indicators
for monitoring by small filtered PWSs.
Cryptosporidium monitoring places a relatively greater economic
burden on small PWSs, and EPA will have additional E. coli and
Cryptosporidium data from large PWS monitoring prior to the initiation
of small PWS monitoring. Based on these considerations and the
available data on E. coli as an indicator of sources with lower
Cryptosporidium levels, the Advisory Committee recommended that small
filtered PWSs initially monitor for E. coli for one year as a screening
analysis. Biweekly sampling (i.e., 1 sample every two weeks) for E.
coli is required to achieve high confidence in the results, since no
additional monitoring is required if the E. coli level is less than the
trigger value. Mean E. coli concentrations above 10 and 50/100 mL
trigger Cryptosporidium monitoring in PWSs using reservoir/lake and
flowing stream sources, respectively.
EPA concurred with these recommendations by the Advisory Committee
and believes they achieve an appropriate balance between enhancing

[[Page 669]]

public health protection and reducing the economic impact of today's
rule on small PWSs. Survey data indicate that approximately 75 to 80
percent of small PWSs will not exceed the E. coli trigger values and,
consequently, will not be required to monitor for Cryptosporidium.
Because E. coli is far less costly to analyze than Cryptosporidium
(costs listed in USEPA 2005a), this approach will significantly reduce
the burden of today's rule for these PWSs. Further, EPA will review
indicator data from large PWS monitoring and, if appropriate, issue
guidance to States on alternative indicator triggers prior to when
small PWSs begin monitoring. Today's rule allows States to approve
alternative approaches to indicator monitoring for small PWSs.
EPA could not identify an indicator screening analysis for
unfiltered PWSs. As described in section IV.C, a mean Cryptosporidium
concentration of 0.01 oocysts/L determines whether unfiltered PWSs are
required to provide 2- or 3-log Cryptosporidium inactivation. No E.
coli concentration was effective in determining whether PWSs were
likely to fall above or below this level. Consequently, today's rule
requires all unfiltered PWSs to monitor for Cryptosporidium, unless
they choose to provide 3-log Cryptosporidium inactivation.
b. Sampling location. The requirements in today's final rule for
the source water sample collection location are similar to those in the
proposed rule (USEPA 2003a). They are designed to achieve two
objectives: (1) Characterize the influent water to the treatment plant
at the time each sample is collected and (2) ensure that samples are
not affected by treatment chemicals that could interfere with
Cryptosporidium analysis.
The first objective is the basis for requiring PWSs that use
multiple sources to either analyze a blended source sample or calculate
a weighted average of sources that reflects the influent at the time of
sample collection. It is also the reason that PWSs are required to
sample after certain pretreatment processes like bank filtration
(described in section IV.D) that do not involve chemical addition.
The second objective is why PWSs are generally required to sample
upstream of chemical addition and prior to backwash addition (for PWSs
that recycle filter backwash). However, EPA recognizes that in some
situations, sampling prior to chemical addition will not be feasible
and discontinuing chemical addition for a period of time prior to
sampling will not be advisable. This situation could occur when a
treatment chemical is added at an intake that is difficult to access.
Further, some treatment chemicals may not interfere with
Cryptosporidium analyses when present at very low levels. Consequently,
today's rule allows States to approve PWSs sampling after chemical
addition when the State determines that collection prior to chemical
treatment is not feasible and the treatment chemical is not expected to
interfere with the analysis of the sample.
EPA believes that States should review source water monitoring
locations for their PWSs. State review of monitoring locations will
ensure that PWSs collect source water samples at the correct location
to determine the appropriate level of public health protection.
Consequently, today's rule requires PWSs to report a description of
their monitoring location to the State. This requirement is a change
from the proposed rule, which did not require PWSs to report a
description of their sampling location (USEPA 2003a). This change
reflects public comment on the proposal, as described later, which
strongly supported State review of monitoring locations. If a PWS does
not hear back from the State by the time it is scheduled to begin
sampling, it may assume that its monitoring location is acceptable.
c. Sampling schedule. The requirement in today's final rule that
PWSs must develop a schedule for sample collection before the start of
monitoring was part of the proposal (USEPA 2003a). This requirement
will help to ensure that monitoring determines the mean concentration
of Cryptosporidium in the treatment plant influent. To achieve this
objective, the timing of sample collection must not be adjusted in
response to fluctuations in water quality--for example, the avoidance
of sampling when the influent water is expected to be of poor quality.
EPA believes that the 5-day window for sample collection and
associated allowances for sampling outside this window provide
sufficient flexibility. If circumstances arise that prevent the PWS
from sampling within the scheduled 5-day window, such as a weather
event or plant emergency, the PWS must collect a sample as soon as
feasible. In this case, feasibility includes both the ability of the
PWS to safely collect a sample and the availability of an approved
laboratory to conduct the analysis within method specifications. In
addition, today's rule allows States to authorize a different date for
collecting the delayed sample. Such an authorization may be appropriate
in cases where sampling is significantly delayed and collecting the
delayed sample during the same time period in the following year of
monitoring is preferable.
PWSs that collect a sample as scheduled but are unable to have the
sample analyzed as required due to problems like shipping or laboratory
analysis must collect a replacement sample within 21 days of receiving
information that one is needed, unless the PWS demonstrates that
collecting a replacement sample within this time frame is not feasible.
This time frame is a minor change from the proposal, which allowed only
14 days for resampling (USEPA 2003a), and it provides greater
flexibility for scheduling replacement samples. Information that
resampling is needed includes information the PWS acquires directly, as
well as notice from the shipping company, laboratory, State, or EPA.
Today's rule allows States to authorize an alternative date for
collection of the replacement sample. This may be needed for resampling
to occur during the same conditions as the originally scheduled sample.
If collecting a sample was feasible but the PWS failed to do so,
EPA believes that the PWSs must develop a revised sampling schedule and
submit it to the State. This will allow for State consultation
regarding the reason for the missed sample(s) and strategies for the
PWS to complete the required monitoring.
d. Plants operating only part of the year. The proposed LT2ESWTR
did not include distinct monitoring requirements for plants that
operate only part-year. However, EPA requested comment in the proposal
on an approach to plants that operate only part-year that is similar to
the requirements in today's final rule (USEPA 2003a).
Monitoring requirements for plants that operate only part-year
derive from three considerations: (1) A PWS should sample only during
the months when a treatment plant operates; (2) the mean
Cryptosporidium level used for bin classification can be determined
with fewer samples in plants that operate only part-year because source
water quality typically varies less during the shorter operating
period; and (3) a minimum number of samples is necessary to classify
any plant in an LT2ESWTR bin with high confidence.
The basis for the first consideration is straightforward. Source
water monitoring under the LT2ESWTR is used to establish treatment
requirements, and these should be based

[[Page 670]]

on the water quality when a plant is in operation. The rationale for
the second and third considerations stems from analyses, similar to
those described previously, of potential misclassification rates in
assigning plants to LT2ESWTR treatment bins.
Source water variability is one factor that influences the number
of samples needed to accurately classify plants in LT2ESWTR treatment
bins. As variability increases, more samples are needed to determine
the mean Cryptosporidium level with high confidence. EPA does not have
data on source water variability specifically in plants that operate
only part-year. However, survey data show that pathogen levels vary
seasonally, and plants operating part-year will generally experience
less variability during a given year than plants operating year-round.
Consequently, fewer samples are typically needed to determine the mean
Cryptosporidium level during the period of operation for a part-year plant.
Nevertheless, even when a plant operates for only a few months per
year and source water exhibits little variability, a minimum number of
samples is necessary for bin classification. This is due to the
relatively low sample volume, variable method recovery, nonhomogeneous
distribution of Cryptosporidium in water, and other factors that limit
the accuracy of any individual sample for characterizing the source
water. Data suggest that for plants operating for six months per year
or less, collecting a minimum of six samples per year over two years
may allow bin classification with comparable accuracy to that achieved
by year-round plants sampling monthly (USEPA 2005a).
Based on these considerations, today's rule requires similar source
water monitoring for plants that operate only part-year during their
months of operation as is required for year-round plants. However, if
the plant is required to monitor for Cryptosporidium and operates for
six months or less, the PWS must collect at least six Cryptosporidium
samples per year over two years.
e. Failing to monitor. Requirements for PWSs that fail to conduct
source water monitoring are based on the need for PWSs to determine a
Cryptosporidium bin classification and provide the appropriate level of
public health protection within the compliance time frame. The LT2ESWTR
proposal required PWSs that did not complete all source water
monitoring requirements to meet the requirements of the highest
treatment bin (USEPA 2003a). In today's final rule, EPA has
significantly changed requirements from those in the proposal for PWSs
that fail to monitor. These changes are intended to give States more
flexibility in working with PWSs to fulfill monitoring requirements and
ensure they achieve the appropriate Cryptosporidium treatment level.
For most monitoring and testing procedure violations under the
LT2ESWTR, PWSs must provide a Tier 3 public notification, which is
standard for this type of violation under an NPDWR. However, if a PWS
fails to collect three or more Cryptosporidium samples, the violation
is elevated to a Tier 2 special public notice. The reason for elevating
the public notice at this point is the persistence of the violation and
the difficulty the PWS will have in collecting the required number of
samples for bin classification by the compliance date. Section IV.H
provides further details on public notice requirements of the LT2ESWTR.
As described in section IV.G, today's rule requires bin
classification within six months following the end of the monitoring
period specified for the PWS. This six-month period provides some
opportunity for collecting and analyzing missed samples. The number of
samples that can be made up in this period is limited, though, due to
the need for samples to be evenly distributed throughout the year, as
well as for PWSs and States to spend time during this period evaluating
monitoring results to determine bin classification. In consideration of
these factors, EPA believes that elevating the public notice when a PWS
has missed three or more Cryptosporidium samples is appropriate. This
violation will end when the State determines that the PWS has begun
sampling on a schedule to collect the required number of samples.
Failure by a PWS to collect the required number of Cryptosporidium
samples for bin classification by the compliance date is a treatment
technique violation with a required Tier 2 public notice. This
violation reflects the inability of the PWS to determine and comply
with its Cryptosporidium treatment requirements under the LT2ESWTR and
provide the appropriate level of public health protection. The
violation ends when the State determines that the PWS is carrying out a
monitoring plan that will lead to bin classification. A PWS that has
already provided a Tier 2 public notice for missing three sampling
dates and is successfully meeting a State-approved sampling schedule is
not required to issue another public notice for missing the bin
classification date. Alternatively, the PWS can choose to provide the
highest level of Cryptosporidium treatment required under the rule,
which is 5.5-log for filtered PWSs and 3-log for unfiltered PWSs.
f. Grandfathering previously collected data. Requirements for
grandfathering previously collected monitoring data in today's final
rule are similar to those in the proposal (USEPA 2003a). These
requirements are based on the principle that to be eligible for
grandfathering, previously collected data must be equivalent in quality
to data that will be collected under the rule.
The Stage 2 M-DBP Advisory Committee recommended that EPA accept
previously collected Cryptosporidium data that are ``equivalent in
sample number, frequency, and data quality (e.g. volume analyzed,
percent recovery) to data that would be collected under the LT2ESWTR *
* * to determine bin classification in lieu of further monitoring''
(USEPA 2000a). The Advisory Committee recognized that accepting
previously collected data could have a number of benefits, including
early determination of LT2ESWTR compliance needs, increasing laboratory
capacity, and allowing PWSs to determine their bin classification using
a larger, and potentially more representative, data set.
To ensure equivalent data quality, today's rule requires that
grandfathered data meet the same requirements for analytical methods,
sampling location, and sample volume as data collected under the rule.
PWSs must not selectively report monitoring results for grandfathering.
Further, grandfathered Cryptosporidium data must generally be collected
at least monthly and on a regular schedule, with the same provisions
for delayed or replacement samples as allowed for regular monitoring.
Today's final rule differs from the proposal, however, in making
allowances for use of previously collected data where irregularities or
gaps in the sampling frequency occur.
EPA recognizes that when PWSs collected Cryptosporidium data prior
to the proposed or final LT2ESWTR, there may have been months when a
PWS either failed to collect or lost a sample due to problems with
equipment, transportation, laboratory analysis, or other reasons. If
the PWS did not collect a replacement sample, gaps in the previously
collected data set occurred. EPA believes that grandfathering of such a
data set may be appropriate despite these gaps if the PWS conducts
additional monitoring, as necessary, to ``fill-in'' gaps and ensure
that the data set is unbiased. Consequently, today's rule allows
grandfathering of data with

[[Page 671]]

gaps in the sampling frequency if approved by the State.
In addition, if the frequency of sampling in a previously collected
data set varies, EPA believes the data could still be appropriate for
use in bin classification. For example, a PWS might have sampled for
Cryptosporidium once per month for a number of months and then
increased the sampling frequency to twice per month. Today's rule
allows the use of such a data set. However, to avoid bias, the PWS must
calculate a monthly average for each month of sampling and then
determine the bin classification using these monthly averages, rather
than the individual sample concentrations.
Today's rule requires PWSs that plan to grandfather monitoring data
to notify EPA or the State regarding the number and time span of sample
results no later than three months prior to when the PWS must begin
monitoring. The timing for submission of this notice is concurrent with
the submission of a sampling schedule. This notification is necessary
for the State to determine that a PWS is not required to submit a
sampling schedule (when a PWS will fully comply with initial monitoring
through grandfathering) or that a sampling schedule may include less
than the full number of required samples (when a PWS will conduct new
monitoring in conjunction with grandfathering to complete a data set).
Further, this notice will assist EPA and States in determining the
resources necessary to ensure timely review of grandfathered data.
PWSs must submit all monitoring results for grandfathering to EPA
or the State, along with required supporting documentation, no later
than two months after the PWS is required to begin monitoring. This
timing will allow a PWS to continue collecting data for grandfathering
until the month the PWS is required to begin monitoring under today's
rule, plus an additional two months for sample analysis and compilation
of the data for submission.
This reporting deadline for grandfathering monitoring results is a
change from the proposed rule. In the proposal, a PWS that intended to
grandfather data in lieu of conducting new monitoring under the rule
had to submit its grandfathered results no later than four months prior
to when the PWS was otherwise required to begin monitoring under the
rule. This proposed approach had the shortcoming that a PWS could not
complete its monitoring for grandfathering within this four month
period. In today's final rule, a PWS may continue monitoring for
grandfathering all the way until the date when the PWS must begin
monitoring under the rule, if necessary. PWSs that conclude their
monitoring for grandfathering earlier may submit the data at an earlier
date.
g. Ongoing watershed assessment. Treatment requirements under the
LT2ESWTR are based on source water quality. Consequently, today's rule
requires watershed assessment and, as described in the next section, a
second round of monitoring following initial bin classification to
determine if source water quality has changed to the degree that the
treatment level should be modified. These requirements are unchanged
from those in the proposed LT2ESWTR (USEPA 2003a), with the exception
of an allowance for States to use programs other than the sanitary
survey to assess changes in the watershed.
Today's rule leverages the existing requirement for States to
perform sanitary surveys on surface water PWSs. During the source water
review in the sanitary survey, today's rule requires States to
determine if significant changes have occurred in the watershed that
could lead to increased contamination by Cryptosporidium. The State can
also choose to make this determination through an equivalent review of
the source water under a program other than the sanitary survey, such
as a Source Water Protection Assessment. If the State determines that
significant changes have occurred, the State may specify that the PWS
conduct additional source water monitoring or treat the potential
contamination. This approach allows the PWS and State to respond to a
significant change in source water quality prior to initiating a second
round of monitoring or any time thereafter.
h. Second round of monitoring. A more rigorous reassessment of the
source water occurs through a second round of monitoring that begins
six years after initial bin classification. If EPA does not develop and
finalize modifications to the LT2ESWTR prior to the date when PWSs must
begin the second round of monitoring, then this second round must
conform to the same requirements that applied to the initial round of
monitoring. PWSs may be classified in a different treatment bin,
depending on the results of the second round of monitoring.
The Stage 2 M-DBP Advisory Committee recommended that EPA initiate
a stakeholder process several years prior to the second round of
monitoring to review new information and determine if today's rule
should be modified. If the Agency modifies the LT2ESWTR, the second
round of monitoring would potentially involve a new analytical method
and a different treatment bin structure.
3. Summary of Major Comments
Public comment on the August 11, 2003, LT2ESWTR proposal generally
supported the use of source water monitoring to determine additional
treatment requirements. The following discussion summarizes major
comments and EPA's responses in regard to sampling parameters and
frequency, sampling location, sampling schedule, monitoring plants that
operate only part-year, failing to monitor, providing treatment instead
of monitoring, grandfathering previously collected data, ongoing source
water assessment, second round of monitoring, and new source monitoring.
a. Sampling parameters and frequency. Most commenters supported the
proposed requirements for large PWSs to sample monthly for
Cryptosporidium, as well as for E. coli and turbidity in filtered PWSs,
for 24 months. Alternatives recommended by some commenters included
ending monitoring after one year if no oocysts are detected, allowing
large PWSs to use an E. coli screening analysis to determine if
Cryptosporidium monitoring is necessary, and using watershed data to
determine treatment needs instead of source water monitoring.
In response, EPA continues to believe that large PWSs should
complete 24 months of Cryptosporidium monitoring, regardless of the
first-year results, in order to capture a degree of annual variability
in Cryptosporidium occurrence. Moreover, for the reasons discussed
previously in this preamble, EPA continues to support the Advisory
Committee recommendation that all large PWSs should monitor for
Cryptosporidium, rather than use the E. coli screening analysis. EPA is
not aware of studies that support the use of other watershed data in
place of Cryptosporidium monitoring to determine treatment needs.
Regarding requirements for small PWSs, most commenters supported
the E. coli screening analysis for small filtered PWSs. Several
commenters recommended more options for Cryptosporidium monitoring by
small PWSs, such as allowing monitoring to be spread over two years,
instead of the one year required in the proposal, or allowing fewer
samples. EPA agrees that budgeting for Cryptosporidium monitoring by
some small PWSs will be easier if it is spread over two years, and
today's rule allows this as an option.

[[Page 672]]

However, based on the analysis of false negative and false positive
rates described previously, EPA continues to believe that at least 24
Cryptosporidium samples are necessary to determine the appropriate bin
classification for year-round plants.
b. Sampling location. With respect to sampling location
requirements, several commenters recommended that PWSs be allowed to
collect samples either before or after pretreatment processes. These
commenters stated that the chemicals used in pretreatment processes are
unlikely to affect the analysis of Cryptosporidium oocysts at typical
concentrations. Further, where sampling is conducted prior to a
pretreatment process like presedimentation, commenters supported
allowing PWSs to receive additional treatment credit for the process.
In response, EPA continues to believe that common pretreatment
chemicals like oxidants and coagulants have the potential to adversely
affect the performance of Cryptosporidium analytical methods.
Consequently, today's rule requires that in most cases, PWSs must
sample upstream of chemical addition. Where PWSs sample prior to
pretreatment processes like presedimentation with coagulation, they are
eligible to receive additional treatment credit for the process.
However, if sampling prior to chemical addition is not feasible for a
particular plant and the treatment chemical is present at a very low
level that is unlikely to interfere with sample analysis, the State may
approve sampling after chemical addition.
Many commenters recommended that States approve sampling locations
for their PWSs. Commenters indicated that State review and approval of
monitoring plans will help to prevent confusion and PWSs potentially
sampling at an incorrect location. EPA agrees with these commenters and
has established a requirement in today's rule for PWSs to report a
description of the sampling location to the State. If a PWS does not
hear back from the State by the time it is scheduled to begin sampling,
it may assume that its monitoring location is acceptable.
c. Sampling schedule. In regard to sampling schedule requirements,
several commenters requested that PWSs be given a time window larger
than 5 days around scheduled sampling dates to collect samples.
Recommended alternatives included a 7 or 9-day window, or only
requiring that PWSs collect a sample within a specified month. In
addition, commenters identified situations that interfere with sample
collection, such as plant interruptions and laboratory or
transportation problems, and noted that some of these are outside the
conditions under which the proposal allowed a PWS to collect a delayed
or replacement sample without penalty.
In response, EPA continues to believe that for routine sample
collection, a 5-day window provides sufficient flexibility, given that
PWSs will pick the sampling days and can schedule around holidays,
weekends, and other times when sampling would be problematic. However,
today's rule allows PWSs to sample outside of this window without
penalty if necessary due to unforeseen conditions. Further, if a PWS
collects a sample but is unable to have it analyzed due to problems
with equipment, transportation or the laboratory, today's rule allows
the PWS to collect a replacement sample without penalty.
In regard to the time frame for collecting missed or replacement
samples, commenters recommended a number of approaches. These include
adding extra sampling days to the original sampling schedule, which a
PWS could then use in the event of missed sampling dates, and allowing
PWSs to collect make-up samples either immediately after the scheduled
sampling date or at the end of the monitoring period.
In general, EPA considers it preferable for PWSs to collect missed
or replacement samples as close as is feasible to scheduled sampling
dates. However, if there is a significant delay with respect to the
original sampling date, collecting make-up samples at an alternate time
may be appropriate to ensure that sampling results are seasonally
representative. Therefore, today's rule requires PWSs to collect a
missed sample as close as is feasible to the scheduled sampling date,
and to collect replacement samples within 21 days of receiving
information that one is needed, unless doing so within this time frame
is not feasible. However, the State can authorize alternative sampling
dates so that monitoring is not seasonally biased. This could include
sampling during the same time in the following year, if the missed
sample occurred during the first year of monitoring, or sampling after
the end of the scheduled monitoring period.
d. Plants operating only part of the year. Commenters on monitoring
requirements for surface water plants that operate for only part of the
year generally recommended that sampling occur only during the period
of operation. However, several different options were put forward for
how the sampling be conducted. Some commenters recommended a minimum of
12 samples per year for two years distributed evenly over the period
that the plant operates. Others suggested allowing the PWS to collect
the required number of samples over a longer time period in order to
limit the frequency of required samples when the plant is operating.
Several commenters said that State input is critical to determining the
appropriate monitoring period since States may have historical
knowledge of plant operating practices.
In response, EPA agrees that monitoring of plants that operate only
part-year under today's rule should be conducted only during months
when the plant is operating, unless the State determines that a longer
monitoring period is appropriate due to historical operating practices.
Further, plants that operate only part-year should maintain the same
sampling frequency as plants operating year-round, with the exception
that plants monitoring for Cryptosporidium must collect at least six
samples per year to allow for appropriate bin classification. EPA does
not believe extending monitoring over more years in plants that operate
only part-year is appropriate, as this would delay the installation of
additional treatment where needed.
e. Failing to monitor. Most commenters opposed automatically
classifying PWSs in the highest treatment bin (Bin 4) if they fail to
complete required monitoring, as the proposed rule stipulated.
Commenters suggested alternative approaches, such as giving States the
flexibility to address missed samples using current enforcement
mechanisms, classifying a PWS only one level higher than the bin
determined by the collected data, allowing an additional year of
sampling, and allowing States to use other information (e.g., sanitary
surveys, other monitoring data) to aid in the classification. A few
commenters, however, supported Bin 4 classification for PWSs that fail
to monitor, on the basis that any other approach would create an
incentive for PWSs to stop testing if poor water quality is suspected.
EPA agrees that States should have flexibility in dealing with PWSs
that fail to monitor. Further, providing the highest level of treatment
may not be in the best interests of consumers where a PWS has minor
problems in carrying out source water monitoring. However, EPA also
believes that violations for monitoring failures must reasonably ensure
that PWSs complete monitoring as required to determine a bin
classification within the compliance

[[Page 673]]

date. Failure to do so would potentially compromise public health
protection.
Based on these considerations, EPA has not established an automatic
Bin 4 classification for monitoring failures under today's rule.
Rather, if a PWS misses three or more Cryptosporidium samples, this
persistent violation requires a Tier 2 public notice (other violations
require a Tier 3 notice). Further, if a PWS is unable to determine a
bin classification by the compliance date due to failure to collect the
required number of Cryptosporidium samples, this is a treatment
technique violation with a required Tier 2 public notice (unless the
PWS has already issued a Tier 2 notice for missing 3 Cryptosporidium
samples and is monitoring on a State-approved schedule). These
violations last until the State determines that a PWS has begun
monitoring on a schedule that will lead to bin classification or the
PWS agrees to install treatment instead of monitoring.
f. Providing treatment instead of monitoring. Commenters supported
the option for a PWS to provide the highest level of Cryptosporidium
treatment required under today's rule rather than conducting source
water monitoring. Several commenters recommended that a PWS should be
allowed to take this option after having initiated monitoring. EPA
agrees, and today's rule allows a PWS to stop monitoring at any time by
notifying the State that it will provide 5.5-log Cryptosporidium
treatment for filtered PWSs or 3-log Cryptosporidium inactivation for
unfiltered PWSs by the compliance deadline specified in section IV.G.
g. Grandfathering previously collected data. With respect to
grandfathering previously collected data, many commenters expressed
concern with a proposed requirement that samples must have been
collected in equal time intervals. Commenters stated that although PWSs
may have sampled on a regular schedule, previously collected data sets
are likely to have gaps due to samples rejected for method QC
violations or periods when the PWS was unable to collect a sample. In
addition, there are instances where PWSs have changed the frequency of
sampling, such as from monthly to twice per month.
EPA agrees that if a PWS has collected samples according to a
regular schedule and met other data quality standards, then rejecting a
large data set due to isolated gaps in the sampling frequency would be
inappropriate. Consequently, today's rule allows States to approve
grandfathering of previously collected data with omissions in the
sampling interval, provided the PWS conducts additional monitoring if
required by the State to ensure the data set is seasonally
representative. Further, PWSs may grandfather previously collected data
sets in which the sampling frequency varies, as long as samples were
collected at least monthly. In this situation, PWSs must use monthly
average concentrations, rather than individual sample concentrations,
for bin classification.
With respect to data quality standards, such as meeting analytical
method QC criteria, sampling at the correct location, and analyzing the
minimum sample volume, several commenters stated that EPA should apply
the same acceptance standards to previously collected data as are
applied to data collected under today's rule. Other commenters, though,
suggested that States should have the flexibility to accept previously
collected data that deviate from the data quality standards for
monitoring under the rule. These commenters stated that such data sets
might include samples collected over a longer period of time and may
reflect more worst-case weather events.
In response, EPA believes that data quality standards should be
uniformly applied under today's rule, so that previously collected data
should not be held to a lower standard than new data or evaluated
differently from State to State. The requirements in today's rule with
respect to Cryptosporidium analytical methods and minimum sample volume
reflect recommendations of the Advisory Committee, which also
recommended that the same data quality standards be applied for
grandfathering. Further, because today's rule allows PWSs to collect
make-up samples to address gaps in previously collected data sets, PWSs
will have the opportunity to collect make-up samples for results that
are rejected due to data quality standards without losing an entire
data set.
In regard to notification of the acceptability of data for
grandfathering, commenters recommended that if previously collected
data submitted by a PWS are rejected, the PWS should have at least two
months between notification and the date new monitoring must be
initiated. These two months will give the PWS time to address rejection
of the data and prepare for sampling. EPA agrees with this
recommendation. Under today's rule, if a PWS properly submits a
complete data set for grandfathering and the PWS must conduct new
monitoring due to rejection of the data, the PWS has at least two
months following notification by the State to initiate sampling.
h. Ongoing watershed assessment. Commenters asked for greater
flexibility in the requirement for States to determine whether there
have been significant changes in the watersheds of their PWSs that
could lead to increased contamination. The proposed rule specified that
States must make this determination during sanitary surveys. However,
several commenters noted that some States perform source water
protection assessments on the same frequency as sanitary surveys, and
these detailed assessments might be a better mechanism to monitor
changes in the watershed. EPA agrees and today's rule allows States to
determine whether significant changes have occurred in the watershed
through either a sanitary survey or an equivalent review of the source
water under another program.
i. Second round of monitoring. Some commenters supported the
proposed requirement for a second round of source water monitoring, but
most opposed requiring it for all PWSs. These commenters recommended
that States should be authorized to use sanitary surveys, source water
assessments, ambient water quality data, treatment plant data, and
other information to determine if a second round of monitoring is
necessary for a PWS. Some commenters suggested that EPA fund research
to allow the use of finished water monitoring as the determinant for
treatment requirements in a second round of monitoring.
In response, EPA continues to believe that PWSs should conduct a
second round of monitoring to determine if the level of treatment
required as a result of the first round of monitoring is still
appropriate. Consequently, today's rule requires this. However, EPA
agrees that prior to a second round of monitoring, the Agency should
evaluate the results of the first round of monitoring, along with
whatever new information is available on Cryptosporidium analytical
methods, risk, and other relevant issues. If EPA determines that there
should be changes to the requirements for a second round of monitoring
in today's rule, the Agency will issue a new rule establishing those
changes.
j. New source monitoring. EPA requested comment in the proposal on
monitoring requirements for new plants and sources (USEPA 2003a). Most
commenters recommended that new plants and sources undergo monitoring
equivalent to that required for existing plants and sources, and
suggested that States should have discretion to determine when
monitoring should take place. EPA agrees with these recommendations and
today's rule requires PWS to conduct source water

[[Page 674]]

monitoring for new plants and sources on a schedule approved by the
State. This schedule must include dates for the PWS to determine its
treatment bin classification and, if necessary, comply with additional
Cryptosporidium treatment requirements.

B. Filtered System Cryptosporidium Treatment Requirements

1. Today's Rule
Today's rule requires filtered PWSs using surface water or GWUDI
sources to provide greater levels of treatment if their source waters
have higher concentrations of Cryptosporidium. Specifically, filtered
PWSs are classified in one of four treatment bins based on results from
the source water monitoring described in the previous section. PWSs
classified in the lowest concentration bin are subject to no additional
treatment requirements, while PWSs assigned to higher concentration
bins must reduce Cryptosporidium levels beyond IESWTR and LT1ESWTR
requirements. All PWSs must continue to comply with the requirements of
the SWTR, IESWTR, and LT1ESWTR, as applicable.
This section addresses procedures for classifying filtered PWSs in
Cryptosporidium treatment bins and the treatment requirements
associated with each bin. Section IV.D presents the treatment and
control options, collectively termed the ``microbial toolbox,'' that
PWSs must use to meet additional Cryptosporidium treatment requirements
under today's rule.
a. Bin classification. After completing initial source water
monitoring, filtered PWSs must calculate a Cryptosporidium bin
concentration for each treatment plant where Cryptosporidium monitoring
is required. This Cryptosporidium bin concentration is used to classify
filtration plants in one of the four treatment bins shown in Table IV.B-1.

Table IV.B-1.--Bin Classification Table for Filtered PWSs
------------------------------------------------------------------------
with a Cryptosporidium The bin
For PWSs that are: bin concentration of . classification
. . is . . .
------------------------------------------------------------------------
* * * required to monitor for less than 0.075 Bin 1.
Cryptosporidium. oocysts/L.
0.075 oocysts/L or Bin 2.
higher, but less than
1.0 oocysts/L.
1.0 oocysts/L or Bin 3.
higher, but less than
3.0 oocysts/L.
3.0 oocysts/L or Bin 4.
higher.
* * * serving fewer than NA.................... Bin 1.
10,000 people and NOT
required to monitor for
Cryptosporidium \1\.
------------------------------------------------------------------------
\1\ Filtered PWSs serving fewer than 10,000 people are not required to
monitor for Cryptosporidium if they monitor for E. coli and
demonstrate a mean concentration of E. coli less than or equal to 10/
100 mL for lake/reservoir sources or 50/100 mL for flowing stream
sources or do not exceed an alternative State-approved indicator
trigger (see section IV.A.1).

In general, the Cryptosporidium bin concentration is calculated by
averaging individual sample results from one or more years of
monitoring. Specific procedures vary, however, depending on the
frequency and duration of monitoring. These procedures are as follows:
(1) For PWSs that collect a total of at least 24 but not more than
47 Cryptosporidium samples over two or more years, the Cryptosporidium
bin concentration is equal to the highest arithmetic mean of all sample
concentrations in any 12 consecutive months of Cryptosporidium monitoring.
(2) For PWSs that collect a total of at least 48 samples, the
Cryptosporidium bin concentration is equal to the arithmetic mean of
all sample concentrations.
(3) For PWSs that serve fewer than 10,000 people and monitor for
Cryptosporidium for only one year (i.e., collect 24 samples in 12
months), the Cryptosporidium bin concentration is equal to the
arithmetic mean of all sample concentrations.
(4) For PWSs with plants that operate only part-year that monitor
for less than 12 months per year, the Cryptosporidium bin concentration
is equal to the highest arithmetic mean of all sample concentrations
during any year of Cryptosporidium monitoring.
In data sets with variable sampling frequency, PWSs must first
calculate an arithmetic mean for each month of sampling and then apply
one of these four procedures using the monthly mean concentrations. As
described in section IV.A, PWSs may grandfather previously collected
Cryptosporidium data where the sampling frequency varies (e.g., one
year of monthly sampling and one year of twice-per-month sampling).
Filtered PWSs serving fewer than 10,000 people are not required to
monitor for Cryptosporidium if they demonstrate a mean E. coli
concentration less than or equal to 10/100 mL for lake/reservoir
sources or 50/100 mL for flowing stream sources or do not exceed an
alternative State-approved indicator trigger. PWSs that meet this
criterion are classified in Bin 1 as shown in Table IV.B-1.
When determining the Cryptosporidium bin concentration, PWSs must
calculate individual sample concentrations as the total number of
oocysts counted, divided by the volume assayed (see section V.K for
details). In samples where no oocysts are detected, the result is
assigned a value of zero for the purpose of calculating the bin
concentration. Sample analysis results are not adjusted for analytical
method recovery or the percent of Cryptosporidium oocysts that are
infectious.
PWSs must report their treatment bin classification to the State
for approval following initial source water monitoring (see section
IV.G for specific compliance dates). The report must include a summary
of the data and calculation procedure used to determine the bin
concentration. If EPA does not amend today's rule before the second
round of monitoring described in section IV.A, PWSs must recalculate
their bin classification after completing the second round of
monitoring and report the results to the State for approval. If the
State does not respond to a PWS regarding its bin classification after
either report, the PWS must comply with the Cryptosporidium treatment
requirements of today's rule based on the reported bin classification.
b. Bin treatment requirements. Table IV.B-2 shows the additional
Cryptosporidium treatment requirements associated with the four
treatment bins for filtered PWSs under today's rule. All filtered PWSs
must comply with these treatment requirements based on their bin
classification, which must be determined using the procedures just
described.

[[Page 675]]

Table IV.B-2.--Treatment Requirements for LT2ESWTR Bin Classifications
----------------------------------------------------------------------------------------------------------------
And you use the following filtration treatment in full compliance with
the SWTR, IESWTR, and LT1ESWTR (as applicable), then your additional
treatment requirements are . . .
--------------------------------------------------------------------------
If your bin classification is . . . Conventional filtration
treatment \1\,
diatomaceous earth Direct filtration Alternative filtration
filtration, or slow technologies
sand filtration
----------------------------------------------------------------------------------------------------------------
Bin 1................................ No additional treatment No additional treatment No additional
treatment.
Bin 2................................ 1-log treatment \2\.... 1.5-log treatment \2\.. As determined by the
State 2 4
Bin 3................................ 2-log treatment \3\.... 2.5-log treatment \3\.. As determined by the
State 3 5
Bin 4................................ 2.5-log treatment \3\.. 3-log treatment \3\.... As determined by the
State 3 6
----------------------------------------------------------------------------------------------------------------
\1\ Applies to a treatment train using separate, sequential, unit processes for coagulation/flocculation,
clarification, and granular media filtration. Clarification includes any solid/liquid separation process
following coagulation where accumulated solids are removed during this separate component of the treatment
system.
\2\ PWSs may use any technology or combination of technologies from the microbial toolbox in section IV.D.
\3\ PWSs must achieve at least 1-log of the required treatment using ozone, chlorine dioxide, UV, membranes, bag
filtration, cartridge filtration, or bank filtration.
\4\ Total Cryptosporidium removal and inactivation must be at least 4.0 log.
\5\ Total Cryptosporidium removal and inactivation must be at least 5.0 log.
\6\ Total Cryptosporidium removal and inactivation must be at least 5.5 log.

The total Cryptosporidium treatment required for plants in Bins 2,
3, and 4 is 4.0-log, 5.0-log, and 5.5-log, respectively. Conventional
treatment (including softening), slow sand, and diatomaceous earth
filtration plants in compliance with the IESWTR or LT1ESWTR, as
applicable, receive a prescribed 3.0-log Cryptosporidium treatment
credit toward these total bin treatment requirements. Accordingly,
these plant types must provide 1.0- to 2.5-log of additional treatment
when classified in Bins 2-4, respectively. Direct filtration plants in
compliance with existing regulations receive a prescribed 2.5-log
treatment credit and, consequently, must achieve 0.5-log greater
treatment to comply with Bins 2-4. Section IV.D describes how States
may award a level of treatment credit that differs from the prescribed
credit based on a demonstration of performance by the PWS.
For PWSs using alternative filtration technologies, such as
membranes, bag filters, or cartridge filters, no prescribed treatment
credit is available because the performance of these processes is
specific to individual products. Consequently, when PWSs using these
processes are classified in Bins 2-4, the State must determine
additional treatment requirements based on the credit the State awards
to a particular technology. The additional treatment requirements must
ensure that plants classified in Bins 2-4 achieve total Cryptosporidium
reductions of 4.0- to 5.5-log, respectively. Section IV.D describes
challenge testing procedures to determine treatment credit for
membranes, bag filters, and cartridge filters.
PWSs can achieve additional Cryptosporidium treatment credit
through implementing pretreatment processes like presedimentation or
bank filtration, by developing a watershed control program, and by
applying additional treatment steps like ozone, chlorine dioxide, UV,
and membranes. In addition, PWSs can receive a higher level of credit
for existing treatment processes through achieving very low filter
effluent turbidity or through a demonstration of performance. Section
IV.D presents criteria for awarding Cryptosporidium treatment credit to
these and other treatment and control options, which collectively
comprise the microbial toolbox.
PWSs in Bin 2 can meet additional Cryptosporidium treatment
requirements by using any option or combination of options from the
microbial toolbox. For Bins 3 and 4, PWSs must achieve at least 1-log
of the additional treatment requirement by using ozone, chlorine
dioxide, UV, membranes, bag filtration, cartridge filtration, or bank
filtration.
2. Background and Analysis
Today's rule will increase protection against Cryptosporidium and
other pathogens in PWSs with the highest source water contamination
levels. This targeted approach builds upon existing regulations under
which all filtered PWSs must provide the same level of treatment
regardless of source water quality. EPA's intent with today's rule is
to ensure that PWSs with higher risk source waters achieve public
health protection commensurate with PWSs with less contaminated sources.
The Cryptosporidium treatment requirements for filtered PWSs in
today's rule are unchanged from the August 11, 2003 proposal (USEPA
2003a) and reflect consensus recommendations by the Stage 2 M-DBP
Advisory Committee (USEPA 2000a). The following discussion summarizes
the Agency's basis for establishing risk-targeted Cryptosporidium
treatment requirements and for setting the specific bin concentration
ranges and treatment requirements that apply to filtered PWSs in
today's rule.
a. Basis for targeted treatment requirements. In developing today's
rule, EPA evaluated the degree to which new information on
Cryptosporidium warranted moving beyond existing regulations. As
discussed in section III, the IESWTR established a Cryptosporidium MCLG
of zero and requires large filtered PWSs to achieve 2-log
Cryptosporidium removal. The LT1ESWTR extended this requirement to
small PWSs. After these rules were promulgated, advances were made in
analytical methods and treatment for Cryptosporidium, and EPA collected
new information on Cryptosporidium occurrence and infectivity.
Consequently, EPA assessed the implications of these developments for
further controlling Cryptosporidium to approach the zero MCLG.
The risk-targeted approach for filtered PWSs in today's final rule
stems from four general findings based on new information on
Cryptosporidium:
(1) New data on Cryptosporidium infectivity suggest that the risk
associated with a particular level of Cryptosporidium is most likely
higher than EPA estimated at the time of earlier rules;
(2) New data on Cryptosporidium occurrence indicate that levels are
relatively low in most water sources, but a subset of sources has
substantially higher concentrations;
(3) The finding that UV light can readily inactivate
Cryptosporidium, as well as other technology developments, makes
achieving high levels of

[[Page 676]]

treatment for Cryptosporidium feasible for PWSs of all sizes; and
(4) EPA Methods 1622 and 1623 are capable of assessing annual mean
levels of Cryptosporidium in drinking water sources.
These findings led EPA to conclude that most filtered PWSs
currently provide sufficient treatment for Cryptosporidium, but
additional treatment is needed in those PWSs with the highest source
water Cryptosporidium levels to protect public health. Further, PWSs
can characterize Cryptosporidium levels in their source waters with
available analytical methods and can provide higher levels of treatment
with available technologies. Consequently, risk-targeted treatment
requirements for Cryptosporidium based on source water contamination
levels are appropriate and feasible to implement.
b. Basis for bin concentration ranges and treatment requirements.
To establish the risk-targeted treatment requirements in today's rule,
EPA had to determine the degree of treatment that should be required
for different source water Cryptosporidium levels to protect public
health. This determination involved addressing several questions:
? What is the risk associated with Cryptosporidium in a
drinking water source?
? How much Cryptosporidium removal do filtration plants
achieve?
? What is the appropriate statistical measure for
classifying PWSs into treatment bins?
? What degree of additional treatment is needed for higher
source water Cryptosporidium levels?
? How should PWSs calculate their treatment bin classification?
This section summarizes how EPA evaluated these questions in
developing today's rule. See the proposed LT2ESWTR for further details
(USEPA 2003a).

What is the Risk Associated With Cryptosporidium in a Drinking Water
Source?

The risk of infection from Cryptosporidium in drinking water is a
function of exposure (i.e., the dose of oocysts ingested) and
infectivity (i.e., likelihood of infection as a function of ingested
dose). Primary (i.e., direct) exposure to Cryptosporidium depends on
the concentration of oocysts in the source water, the fraction removed
by the treatment plant, and the volume of water consumed (secondary
exposure occurs through interactions with infected individuals). Thus,
the daily risk of infection (DR) is as follows:

DR = (oocysts/L in source water) x (fraction remaining after treatment)
x (liters consumed per day) x (likelihood of infection per oocyst dose).

Assuming 350 days of consumption per year for people served by
community water systems (CWSs), the annual risk (AR) of infection is as
follows:

AR = 1 - (1 - DR) \350\.

As discussed in section III.E, EPA has estimated the mean
likelihood of infection from ingesting one Cryptosporidium oocyst to
range from 4 to 16 percent. Median individual daily water consumption
is estimated as 1.07 L/day. Figure IV.B-1 illustrates ranges for the
annual risk of infection by Cryptosporidium in CWSs based on these
values for different source water infectious oocyst concentrations and
treatment plant removal efficiencies. The dashed lines represent the
uncertainty associated with Cryptosporidium infectivity for each log-
removal curve. See Chapter 5 of the LT2ESWTR Economic Analysis for
details (USEPA 2005a).
BILLING CODE 6560-50-P

[[Page 677]]
[GRAPHIC]
[TIFF OMITTED]
TR05JA06.000

BILLING CODE 6560-50-C
The results in Figure IV.B-1 show, for example, that if a treatment
plant had a concentration of infectious Cryptosporidium in the source
water of 0.1 oocysts/L and the plant achieved 3-log removal, the mean
annual risk of

[[Page 678]]

Cryptosporidium infection would range from 0.0017 to 0.0060 (17 to 60
infections per 10,000 consumers). In comparison, if the same plant had
a source water infectious Cryptosporidium level of 0.01 oocysts/L, the
annual infection risk would range from 1.7 to 6 per 10,000 consumers.

How much Cryptosporidium removal do filtration plants achieve?

The amount of Cryptosporidium removal that filtration plants
achieve was a key factor in assessing the additional treatment that
plants with higher source water Cryptosporidium levels should provide.
To evaluate this factor, EPA reviewed studies of Cryptosporidium
removal by common treatment processes. As described in the proposal for
today's rule, these processes were conventional treatment, direct, slow
sand, and diatomaceous earth filtration, as well as membrane, bag, and
cartridge filtration (USEPA 2003a).
The majority of plants treating surface water use conventional
treatment, which is defined in 40 CFR 141.2 as coagulation,
flocculation, sedimentation, and filtration. In the proposal, EPA
reviewed studies of conventional treatment by Dugan et al. (2001),
Nieminski and Bellamy (2000), McTigue et al. (1998), Patania et al.
(1999), Huck et al. (2000), Emelko et al. (2000), and Harrington et al.
(2001). Based on these studies, EPA estimated that conventional
treatment plants in compliance with the IESWTR or LT1ESWTR typically
achieve a Cryptosporidium removal efficiency of approximately 3-log.
Consequently, conventional treatment plants receive 3-log credit toward
Cryptosporidium treatment requirements under today's rule.
This 3-log credit for conventional treatment is consistent with the
Stage 2 M-DBP Agreement in Principle (USEPA 2000a), which states as
follows:

``The additional treatment requirements in the bin requirement
table are based, in part, on the assumption that conventional
treatment plants in compliance with the IESWTR achieve an average of
3 logs removal of Cryptosporidium.''

The M-DBP Advisory Committee did not recommend a level of
Cryptosporidium treatment credit for other types of filtration plants.
EPA also reviewed studies of the performance of clarification
processes like dissolved air flotation, which can be used in place of
sedimentation in a conventional treatment train (Gregory and Zabel
1990, Plummer et al. 1995, Edzwald and Kelley 1998). These studies
indicate that plants using clarification processes other than
sedimentation that are located after coagulation and prior to
filtration can achieve performance equivalent to conventional treatment
plants. As a result, any treatment train that includes coagulation/
flocculation, clarification, and granular media filtration is regarded
as conventional treatment for purposes of awarding treatment credit
under today's rule. The clarification step must be a solid/liquid
separation process where accumulated solids are removed during this
separate component of the treatment system.
Direct filtration plants use coagulation, flocculation, and
filtration processes just as conventional treatment plants do, but they
lack a sedimentation basin or equivalent clarification process. In the
proposal, EPA reviewed studies of sedimentation by Dugan et al. (2001),
States et al. (1997), Edzwald and Kelly (1998), Payment and Franco
(1993), Kelly et al. (1995), and Patania et al. (1995). Results from
these studies demonstrate that sedimentation basins can achieve 0.5-log
or greater Cryptosporidium removal. In addition, some studies have
observed that direct filtration achieves less Cryptosporidium removal
than conventional treatment (Patania et al. 1995) and the incidence of
Cryptosporidium in the treated water is higher (McTigue et al. 1998).
Given these findings, EPA has awarded direct filtration plants a 2.5-
log credit towards Cryptosporidium treatment requirements under today's
rule (i.e., 0.5-log less credit than for conventional treatment).
Slow sand filtration involves passing raw water through a bed of
sand at low velocity and without prior coagulation. Diatomaceous earth
filtration is a process by which a filtration medium is initially
deposited onto a support membrane and medium is added throughout the
operation to keep the filter from clogging. In the proposal, EPA
reviewed slow sand filtration studies by Fogel et al. (1993), Hall et
al. (1994), Schuler and Ghosh (1991), and Timms et al. (1995) and
diatomaceous earth filtration studies by Schuler and Gosh (1990) and
Ongerth and Hutton (1997, 2001). For both processes, these studies
indicate that a well-designed and properly operated filter can achieve
Cryptosporidium removal efficiencies similar to those observed for
conventional treatment plants. Slow sand and diatomaceous earth
filtration plants, therefore, receive a 3-log credit towards
Cryptosporidium treatment requirements under today's rule.
Estimating a typical Cryptosporidium removal efficiency for
filtration technologies like membranes, bag filters, and cartridge
filters is not possible because the performance of such filters is
specific to a particular product. As a result, credit for these devices
must be determined by the State based on product-specific testing using
the procedures described in section IV.D or other criteria approved by
the State.
Table IV.B-3 summarizes the credits various types of filtration
plants receive toward Cryptosporidium treatment requirements under
today's rule. This credit determines the degree of additional treatment
that plants classified in Bins 2-4 must apply, as shown in Table IV.B-2.

Table IV.B-3.--Cryptosporidium Treatment Credit Towards LT2ESWTR Requirements \1\
----------------------------------------------------------------------------------------------------------------
Conventional
treatment Slow sand or Alternative
Plant type (includes Direct filtration diatomaceous earth filtration
softening) filtration technologies
----------------------------------------------------------------------------------------------------------------
Treatment credit................ 3.0-log........... 2.5-log........... 3.0-log........... Determined by
State. \2\
----------------------------------------------------------------------------------------------------------------
\1\ Applies to plants in full compliance with the IESWTR or LT1ESWTR as applicable.
\2\ Credit must be determined through product or site-specific assessment.

As discussed previously, studies indicate that conventional
treatment plants producing very low filtered water turbidity can
achieve a higher level of Cryptosporidium removal than 3-log, and
today's rule allows such plants to receive additional treatment credit.
Further, States can award a higher or lower level of credit to an
individual plant based on a site-specific demonstration of performance.
Section IV.D provides details on both of these topics.
The Cryptosporidium removal credits for filtration plants in
today's rule differ from the amount of credit awarded under the IESWTR
and LT1ESWTR. As

[[Page 679]]

discussed in section III, those rules require all filtered PWSs to
achieve 2-log removal of Cryptosporidium. PWSs using conventional
treatment, or direct, slow sand, or diatomaceous earth filtration are
in compliance with this requirement if they meet specified filtered
water turbidity standards. These regulatory criteria were based on
consideration of the minimum level of removal that all these filtration
processes will achieve (USEPA 1998a). However, in the risk assessments
that supported these regulations, EPA estimated that most filtration
plants will achieve significantly more removal, with median
Cryptosporidium reductions near 3-log.
Today's rule will supplement IESWTR and LT1ESWTR requirements by
mandating additional treatment at certain PWSs based on source-water
Cryptosporidium levels. When assessing the need for additional
treatment at potentially higher risk PWSs, EPA believes that
considering the full removal efficiency achieved by different types of
treatment plants is appropriate. Because making a site-specific
assessment of removal efficiency at all treatment plants individually
is not feasible, establishing prescribed treatment credits based on
available data is necessary. Accordingly, EPA has concluded that
available data support the higher levels of prescribed credit towards
Cryptosporidium treatment requirements for filtration plants
established by today's rule.

What is the appropriate statistical measure for classifying PWSs into
treatment bins?

EPA and the Advisory Committee evaluated different statistical
measures for characterizing Cryptosporidium monitoring results to
determine if additional treatment should be required. These measures
included the arithmetic mean, median, 90th percentile, and maximum.
EPA concluded, consistent with Advisory Committee recommendations,
that Cryptosporidium levels should be characterized by an arithmetic
mean. This conclusion is based on two factors: (1) Available data
suggest that the mean concentration directly relates to the average
risk of the exposed population (i.e., drinking water consumers); and
(2) with a limited number of samples, the mean can be estimated more
accurately than other statistical measures, such as a 90th percentile
estimate.

What degree of additional treatment is needed for higher source water
Cryptosporidium levels?

Development of the risk-based treatment requirements in today's
rule involved first determining the threshold source-water
Cryptosporidium level at which filtered PWSs should provide additional
treatment to protect public health. The key factors in making this
determination were the estimations of Cryptosporidium risk and
treatment plant removal efficiency discussed previously, along with the
performance of analytical methods for classifying PWSs in different
treatment bins.
EPA and Advisory Committee deliberations focused on mean source-
water Cryptosporidium concentrations in the range of 0.01 to 0.1
oocysts/L as threshold levels for requiring additional treatment. Based
on the type of risk information shown in Figure IV.B-1, these levels
are estimated to result in an annual infection risk in the range of 1.7
x 10-4 to 6.0 x 10-3 (or 1.7 to 60 infections per
10,000 consumers) for a treatment plant achieving 3-log Cryptosporidium
removal (the treatment efficiency estimated for conventional plants
under existing regulations).
A shortcoming with establishing the threshold for additional
treatment at 0.01 oocysts/L, however, is that a PWS would exceed this
concentration with only a very few oocysts being detected. For a PWS
collecting monthly 10-L samples and bin classification based on the
maximum running annual average, as required under today's rule,
detecting two oocysts during one year of monitoring would exceed a mean
of 0.01 oocysts/L. Given the uncertainty associated with
Cryptosporidium monitoring, EPA and the Advisory Committee did not
support requiring additional treatment for filtered PWSs based on so
few counts. Although this shortcoming could theoretically be addressed
by a higher sampling frequency, the feasibility of increased sampling
is limited by the capacity of laboratories and the cost of sample analysis.
A related concern in establishing the threshold concentration for
requiring additional treatment was bin misclassification. If the
threshold concentration was set at 0.1 oocysts/L, for example, some
PWSs with actual mean source-water concentrations greater than this
level would measure a concentration less than this level and would be
misclassified in the bin that requires no additional treatment.
Consequently, they would not provide sufficient public health
protection. As discussed previously, this type of error is due to the
limited number and volume of samples that can be analyzed, imperfect
method recovery, and variability in Cryptosporidium occurrence.
Based on these considerations, the Advisory Committee recommended
and today's rule establishes that filtered PWSs must provide additional
treatment for Cryptosporidium when their mean source-water
concentration exceeds 0.075 oocysts/L. At this concentration, PWSs
collecting monthly 10-L samples must count at least nine oocysts in one
year (9 oocysts per 120 L total sample volume) before additional
treatment is required. Further, any PWS with a mean source-water
infectious Cryptosporidium level above 0.1 oocysts/L, which corresponds
to an estimated infection risk range of 1.7 to 6.0 x 10-3,
is highly likely to be appropriately classified in a bin requiring
additional treatment.
After identifying this first threshold for requiring additional
treatment, determining the Cryptosporidium concentrations that should
bound higher treatment bins was necessary. In making these
determinations, EPA concurred with Advisory Committee recommendations
that sought to balance the possibility of bin misclassification against
equitable risk reduction and public health protection.
Treatment bins that span a wider concentration range result in
lower bin misclassification rates. The analysis summarized in section
IV.A shows that the monitoring required under today's rule can
accurately characterize a PWS's mean Cryptosporidium level within a
0.5-log margin, but error rates increase for smaller margins (USEPA
2005a). Conversely, treatment bins that span a narrower concentration
range provide more equitable protection from risk among different PWSs.
This is due to identical treatment requirements applying to all PWSs in
the same bin. In consideration of these issues, today's rule
establishes two higher treatment bins at Cryptosporidium concentrations
of 1.0 oocysts/L and 3.0 oocysts/L. These values result in the four
bins shown in Table IV.B-1. Available occurrence data indicate that few
PWSs will measure mean Cryptosporidium concentrations greater than 3.0
oocysts/L, so there is no need to establish a treatment bin above this level.
With respect to the degree of additional Cryptosporidium treatment
that PWSs in Bins 2-4 must provide, EPA and the Advisory Committee
considered values of 0.5-log and greater. Today's rule establishes a 1-
log additional treatment requirement for conventional plants in Bin 2.
Because

[[Page 680]]

the concentration range of Bin 2 spans approximately one order of
magnitude, this degree of treatment ensures that plants classified in
Bin 2 will achieve treated water Cryptosporidium levels comparable to
plants in Bin 1. Conventional plants in Bins 3 and 4 must provide 2.0-
and 2.5-log of additional treatment, respectively. As recommended by
the Advisory Committee, these higher additional treatment levels are
required based on the recognition that plants in Bins 3 and 4 have a
much greater potential vulnerability to Cryptosporidium. Consequently,
significantly higher treatment is appropriate to protect public health.
These additional treatment requirements for conventional treatment
plants in Bins 2-4 are based on a prescribed 3-log Cryptosporidium
treatment credit for compliance with the IESWTR or LT1ESWTR, as
discussed previously. They translate to total Cryptosporidium treatment
requirements of 4.0-, 5.0-, and 5.5-log for Bins 2, 3, and 4,
respectively. Plants receiving higher or lower levels of prescribed
treatment credit are required to provide less or more additional
treatment if classified in Bins 2-4.
Plants using slow sand or diatomaceous earth filtration, which also
receive a 3-log treatment credit, incur the same additional treatment
requirements as conventional plants if classified in Bins 2-4. Direct
filtration plants, however, must provide 0.5-log greater additional
treatment if classified in Bins 2-4 because they receive a 2.5-log
prescribed credit. EPA expects, though, that most direct filtration
plants will be classified in Bin 1 because direct filtration is
typically applied only to higher quality source waters.
Because EPA is unable to establish a prescribed treatment credit
for other types of filtration technologies like membranes, bag filters,
and cartridge filters, today's rule requires that States assign a
treatment credit to a particular filtration product. This credit then
determines the amount of additional treatment that a plant using this
product must provide if classified in Bins 2-4 in order to achieve the
required total treatment level. Section IV.D provides criteria for
assigning Cryptosporidium treatment credit to membranes, bag filters,
and cartridge filters.
As described in Section IV.D, today's rule establishes a wide range
of treatment and control options through the microbial toolbox for PWSs
to meet additional Cryptosporidium treatment requirements. PWSs may
choose any option or combination of options from the microbial toolbox
to meet the treatment requirements of plants in Bin 2. For plants in
Bins 3 or 4, though, PWSs must achieve at least 1-log of the additional
treatment requirement using UV, ozone, chlorine dioxide, membranes, bag
filters, cartridge filters, or bank filtration. EPA is establishing
this provision in today's rule as recommended by the Advisory Committee
because these processes will serve as significant additional treatment
barriers for PWSs with the highest levels of pathogens in their sources.

How should PWSs calculate their treatment bin classification?

The specific calculations that PWSs use to determine their bin
classification are based on analyses of misclassification rates and
bias. As described in section IV.A, today's rule requires PWSs to
collect at least 24 samples (except for plants that operate only part-
year) when they monitor for Cryptosporidium. Most PWSs will collect
these 24 samples over two years, but PWSs may sample at a higher
frequency and small PWSs may complete this monitoring in one year.
These differences affect the bin classification calculation.
PWSs that sample monthly over two years (24 samples total) must use
the maximum running annual average (Max-RAA) for bin classification
because this achieves a low false negative rate (the likelihood a PWS
will be incorrectly classified in a lower bin). In comparison, if such
PWSs used the mean of all samples over two years for bin
classification, the false negative rate would be almost four times
higher (see Table IV.B.4).
PWSs that choose to sample at least twice per month over two years
(48 samples total) must use the mean of all 48 samples for their bin
classification. This approach achieves a low false negative rate
similar to the Max-RAA for 24 samples and, in addition, reduces the
false positive rate (the likelihood a PWS will be incorrectly
classified in higher bin--see Table IV.B.4). Due to the lower false
positive rate associated with 48 samples, EPA expects that some PWSs
will choose to sample for Cryptosporidium twice per month.
Small PWSs (serving fewer than 10,000 people) that complete their
Cryptosporidium monitoring over one year must use the mean of all 24
samples for bin classification. This approach has a higher false
negative rate than the approaches allowed for PWSs that monitor over
two years. However, it is the only feasible option for PWSs that
conduct just one year of Cryptosporidium sampling. Averaging sample
concentrations over less than one year is not appropriate (except in
the case of plants that operate only part-year that monitor for less
than one year) as this would bias the bin classification due to
seasonal variation in water quality.

Table IV.B-4.--False Positive and False Negative Rates for Monitoring
and Binning Strategies Considered for the LT2ESWTR
------------------------------------------------------------------------
False False
Strategy positive 1 negative 2
------------------------------------------------------------------------
48 sample arithmetic mean..................... 1.7% 1.4%
24 sample Max-RAA............................. 5.3% 1.7%
24 sample arithmetic mean..................... 2.8% 6.2%
------------------------------------------------------------------------
1 False positive rates calculated for systems with Cryptosporidium
concentrations 0.5 log below the Bin 1 boundary of 0.075 oocysts/L.
2 False negative rates calculated for systems with Cryptosporidium
concentrations 0.5 log above the Bin 1 boundary of 0.075 oocysts/L.

Two additional considerations that relate to characterizing
Cryptosporidium monitoring results to determine treatment requirements
are (1) fewer than 100 percent of oocysts in a sample are recovered and
counted by the analyst and (2) not all the oocysts measured with
Methods 1622 or 1623 are capable of causing infection. These two
factors are offsetting, in that oocyst counts not adjusted for recovery
tend to underestimate the true concentration, while the total oocyst
count typically overestimates the infectious concentration that
presents a health risk.
As described in section III, matrix spike data indicate that
average recovery of Cryptosporidium oocysts with Methods 1622 or 1623
in a national monitoring program will be approximately 40 percent.
Regarding the fraction of oocysts that are infectious, LeChevallier et
al. (2003) tested natural waters for Cryptosporidium using both Method
1623 and a method (cell culture-PCR) to test for infectivity. Results
suggested that 37 percent of the Cryptosporidium oocysts detected by
Method 1623 were infectious. This finding is consistent with the
observation that 37 percent of the oocysts counted during the ICRSS
using Methods 1622 or 1623 had internal structures, which indicate a
higher likelihood of infectivity (among the remaining oocysts, 47
percent had amorphous structures and 16 percent were empty).
While it is not possible to establish a precise value for method
recovery or the fraction of oocysts that are infectious,

[[Page 681]]

available data suggest that these parameters may be of similar
magnitude. Consequently, the Advisory Committee recommended that
monitoring results should not be adjusted to account for either
recovery or the fraction infectious. EPA concurs with this
recommendation and today's rule requires that PWSs be classified in
treatment bins using the total number of Cryptosporidium oocysts
counted, without further adjustment. The LT2ESWTR treatment bins in
today's rule are constructed to reflect this approach.
3. Summary of Major Comments
For filtered PWS treatment requirements in the LT2ESWTR proposal,
EPA received significant public comment on the risk-based approach to
requiring additional treatment, the role of States in determining bin
classification, and the treatment credit for filtration plants. The
following discussion summarizes comments in these areas and EPA's responses.
Most commenters supported the risk-based approach of the LT2ESWTR
in which filtered PWSs monitor for microbial contaminants and only
those PWSs finding higher levels of contamination are required to
provide additional treatment for Cryptosporidium. Among these comments,
many stated support for the four treatment bins for filtered PWSs, with
some noting that future research will indicate whether the bins should
be restructured in a later rulemaking. Several commenters expressed
support for EPA's combination of the Stage 2 DBPR and LT2ESWTR as
essential to creating a balanced approach between DBP control and
microbial risk.
A few commenters opposed the expenditure of funds to reduce risk
from Cryptosporidium on the basis that epidemiological evidence
suggests this risk is low and most communities have not experienced
cryptosporidiosis outbreaks. EPA agrees that additional treatment for
Cryptosporidium in drinking water is not warranted in all communities.
Under today's rule, most PWSs are expected to be classified in the
lowest bin, which requires no additional treatment. However, based on
risk information presented in USEPA (2005a) and summarized in this
preamble, EPA believes that additional treatment is necessary to
protect public health in PWSs with the highest Cryptosporidium levels.
Further, as described in USEPA (2005a), EPA's assessment of
Cryptosporidium risk in drinking water is consistent with the limited
available epidemiological data on disease incidence.
With respect to the role of States in bin classification, most
commenters recommended that States assign or approve the bin
classification for their PWSs. Commenters maintained that State
approval of bin classification is an inherent governmental function and
will avoid confusion as to the level of treatment each PWS must
provide. Further, the approval process will provide an opportunity for
dialog between States and PWSs. EPA agrees with these comments and
today's rule requires PWSs to submit their calculation of bin
classification to the State for review. If the PWS does not hear back
from the State, it must proceed to apply the level of treatment
appropriate for its calculated bin classification in accordance with
its applicable compliance schedule.
In regard to the Cryptosporidium treatment credit that should be
awarded to filtration plants, many commenters supported the 3-log
Cryptosporidium removal credit for conventional treatment and slow sand
filtration. Some comments included data showing that conventional
treatment can achieve greater than 4-log removal of Cryptosporidium,
and several commenters stated concerns that EPA has underestimated the
level of treatment achievable through conventional treatment.
Commenters supported the inclusion of plants using softening and
dissolved air flotation for conventional treatment credit and requested
that EPA extend this credit to similar treatment trains using other
types of clarification processes.
EPA recognizes that studies show conventional treatment can achieve
more than 3-log Cryptosporidium removal under optimal conditions.
However, studies also demonstrate that removal efficiencies can be
significantly less for suboptimal plant set-up and operation. EPA does
not expect that all plants will operate under optimal conditions at all
times. Consequently, today's rule awards a prescribed 3-log credit to
conventional plants complying with the IESWTR or LT1ESWTR and allows
plants to receive higher credit through demonstrating low finished
water turbidity or through an alternative demonstration of performance,
as describe in section IV.D. EPA agrees that plants using alternative
clarification process that involves solids removal between coagulation
and filtration should qualify for 3-log credit and today's rule
provides for this.

C. Unfiltered System Cryptosporidium Treatment Requirements

1. Today's Rule
Today's rule requires all PWSs that use a surface water or GWUDI
source and are unfiltered to provide treatment for Cryptosporidium. The
degree of required treatment depends on the level of Cryptosporidium in
the source water, as determined through required monitoring. Further,
unfiltered PWSs must meet overall treatment requirements using at least
two disinfectants and must continue to meet all applicable filtration
avoidance criteria. Details of these requirements follow.
a. Determination of mean Cryptosporidium level. Following
completion of the required initial source water monitoring described in
section IV.A, each unfiltered PWS must determine the arithmetic mean of
all its Cryptosporidium sample results generated during the monitoring
period. As required for filtered PWSs, individual sample results must
be calculated as the total number of oocysts counted, divided by the
volume assayed (see section V.K for details). Samples are not adjusted
for method recovery and, in samples where no oocysts are detected, the
result is treated as zero.
Unfiltered PWSs must report their mean Cryptosporidium level to the
State for approval (see section IV.G for specific reporting dates). The
report must include a summary of the data used to determine the mean
concentration. If the State does not respond to a PWS regarding its
mean Cryptosporidium level, the PWS must comply with the
Cryptosporidium treatment requirements of today's rule, as described
next, based on the reported level.
If EPA does not amend today's rule before the second round of
monitoring described in section IV.A, unfiltered PWSs must recalculate
their mean Cryptosporidium level using results from the second round of
monitoring. Unfiltered PWSs must report this level to the State as
described for the initial round of monitoring.
b. Cryptosporidium treatment requirements. Unfiltered PWSs must
comply with the following treatment requirements based on their mean
source-water Cryptosporidium level: if the level is less than or equal
to 0.01 oocysts/L then at least 2-log Cryptosporidium inactivation is
required; if the level is greater than 0.01 oocysts/L, or if the
unfiltered PWS chooses not to monitor for Cryptosporidium, then at
least 3-log Cryptosporidium inactivation is

[[Page 682]]

required. See section IV.G for treatment compliance dates.
EPA has developed criteria, described in section IV.D, to award
Cryptosporidium inactivation credit for treatment with chlorine
dioxide, ozone, or UV light. Unfiltered PWSs may use any of these
disinfectants to meet their Cryptosporidium inactivation requirements
under today's rule. Further, unfiltered PWSs must achieve the following
with respect to disinfection treatment:
(1) A PWS that uses chlorine dioxide or ozone and fails to achieve
the required level of Cryptosporidium inactivation on more than one day
in the calendar month is in violation of the treatment technique
requirement.
(2) A PWS that uses UV light and fails to achieve the required
level of Cryptosporidium inactivation in at least 95 percent of the
water delivered to the public every month is in violation of the
treatment technique requirement.
c. Use of two disinfectants. Unfiltered PWSs must use at least two
different disinfectants to provide 4-log virus, 3-log Giardia lamblia,
and 2- or 3-log Cryptosporidium inactivation as required under 40 CFR
141.72(a) and today's rule. Further, each of two disinfectants must
achieve by itself the total inactivation required for one of these
target pathogens. This requirement does not modify the existing
requirement under 40 CFR 141.72(a) for PWSs to provide a disinfectant
residual in the distribution system.
2. Background and Analysis
The intent of the Cryptosporidium treatment requirements for
unfiltered PWSs in today's final rule is to ensure that they achieve
public health protection equivalent to that achieved by filtered PWSs.
These requirements are unchanged from the August 11, 2003 proposal
(USEPA 2003a), and they reflect consensus recommendations by the Stage
2 M-DBP Advisory Committee (USEPA 2000a). The following discussion
summarizes the Agency's basis for establishing risk-targeted
Cryptosporidium treatment requirements for unfiltered PWSs in today's
rule and for requiring the use of two disinfectants.
a. Basis for Cryptosporidium treatment requirements. As described
in section III, available data suggest that unfiltered PWSs must take
additional steps to achieve public health protection against
Cryptosporidium equivalent to that provided by filtered PWSs.
In occurrence data from the ICR, the median Cryptosporidium level
in unfiltered PWS sources was 0.0079 oocysts/L, which is approximately
10 times less than the median level of 0.052 oocysts/L in filtered PWS
sources. In translating these source water levels to finished water
concentrations, EPA and the Advisory Committee assumed that
conventional filtration treatment plants in compliance with the IESWTR
or LT1ESWTR achieve an average of 3-log (99.9 percent) removal of
Cryptosporidium. Existing regulations do not require unfiltered PWSs to
provide any treatment for Cryptosporidium.
If the median source water Cryptosporidium level in filtered PWSs
is approximately 10 times higher than in unfiltered PWSs, and filtered
PWSs achieve 3-log Cryptosporidium removal, then the median finished
water Cryptosporidium level in filtered PWSs is approximately 100 times
lower than in unfiltered PWSs. Thus, these data suggest that most
unfiltered PWSs must provide 2-log Cryptosporidium treatment to ensure
equivalent public health protection.
Some unfiltered PWSs must provide greater than 2-log
Cryptosporidium treatment to ensure equitable protection, depending on
their source water level. Under today's rule, the Cryptosporidium
treatment requirements for filtered PWSs, as described in section
IV.B.1, will achieve mean finished water Cryptosporidium levels of less
than 1 oocyst/10,000 L. An unfiltered PWS with a mean source water
Cryptosporidium concentration above 0.01 oocysts/L would have to
provide at least 3-log inactivation to achieve an equivalent finished
water Cryptosporidium level.
As stated earlier, EPA has determined that UV light is a feasible
technology for PWSs of all sizes, including unfiltered PWSs, to
inactivate Cryptosporidium. In addition, treating for Cryptosporidium
using ozone is feasible for some unfiltered PWSs. Inactivating
Cryptosporidium with chlorine dioxide, while allowed under today's
rule, does not appear to be feasible for most unfiltered PWSs due to
regulatory limits on chlorite--a chlorine dioxide byproduct.
Based on these findings, today's rule requires all unfiltered PWSs
to provide at least 2-log Cryptosporidium inactivation, and to provide
at least 3-log inactivation if the mean source water level exceeds 0.01
oocysts/L. These treatment requirements will ensure that unfiltered
PWSs achieve public health protection against Cryptosporidium that is
comparable to filtered PWSs in the finished water that is distributed
to consumers.
Available data indicate that no unfiltered PWSs will show measured
mean source water Cryptosporidium levels of 0.075 oocysts/L or higher--
the level at which a filtered PWS must provide at least 4-log
Cryptosporidium under today's rule. Consequently, EPA is not
establishing treatment requirements in today's rule to address
Cryptosporidium at this higher level. Under existing regulations (40
CFR 141.171 and 141.521), unfiltered PWSs must maintain a watershed
control program that minimizes the potential for contamination by
Cryptosporidium oocysts in the source water. If the measured mean
Cryptosporidium level in an unfiltered PWS is 0.075 oocysts/L or
higher, EPA believes the State should critically evaluate the adequacy
of the watershed control program.
Under today's rule, unfiltered PWSs using ozone or chlorine dioxide
to treat for Cryptosporidium must demonstrate the required 2- or 3-log
inactivation every day the PWS serves water to the public, except any
one day each month. Existing regulations (40 CFR 141.72(a)(1)) require
unfiltered PWSs to ensure inactivation of 3-log Giardia lamblia and 4-
log viruses every day except any one day per month. Consequently,
today's rule extends this compliance standard to Cryptosporidium
inactivation.
For unfiltered PWSs that use UV to treat for Cryptosporidium,
today's rule requires demonstration of the required 2- or 3-log
inactivation in at least 95 percent of the water delivered to the
public every month. EPA intends this standard to be comparable to the
``every day except any one day per month'' standard established for
ozone and chlorine dioxide. Because UV disinfection systems will
typically consist of multiple reactors that will be monitored
continuously, EPA believes that a compliance standard based on the
percentage of water disinfected to the required level is more
appropriate than a single daily measurement. Section IV.D describes an
equivalent standard for filtered PWSs.
b. Basis for requiring the use of two disinfectants. Unfiltered
PWSs must use at least two different disinfectants to meet the
inactivation requirements for Cryptosporidium (2- or 3-log), Giardia
lamblia (3-log) and viruses (4-log), and each of two disinfectants must
achieve by itself the total inactivation required for one of these
target pathogens. For example, a PWS could use UV light to achieve 3-
log inactivation of Giardia lamblia and Cryptosporidium and use
chlorine to provide 4-log virus inactivation. The use of two
disinfectants protects public health by creating multiple barriers
against microbial pathogens. This has two

[[Page 683]]

general advantages over a single barrier: improved reliability and a
broader spectrum of efficacy.
Because unfiltered PWSs rely solely on inactivation for microbial
treatment, an unfiltered PWS using only one disinfectant would provide
no primary microbial treatment if that disinfection process were to
fail. While disinfection processes should be designed for a high level
of reliability, they are not generally 100 percent reliable. Existing
regulations and today's rule recognize this limitation by allowing
unfiltered PWSs to fail to achieve required disinfection levels one day
per month. Consequently, EPA believes that for effective public health
protection, unfiltered PWSs should use at least two primary
disinfection processes. If one process fails, a second process will
provide some degree of protection against pathogens.
A second advantage of a PWS using multiple disinfectants is that
this approach will typically be more effective against a broad spectrum
of pathogens. The efficacy of different disinfectants against different
types of pathogens varies widely. For example, UV light appears to be
very effective for inactivating protozoa like Cryptosporidium and
Giardia lamblia, but is less effective against certain enteric viruses
like adenovirus. Chlorine, however, is highly effective against enteric
viruses but less effective against protozoa. As a result, multiple
disinfectants will generally provide more effective inactivation of a
wide range of pathogens than a single disinfectant.
c. Filtration avoidance. Today's rule does not withdraw or modify
any existing criteria for avoiding filtration under 40 CFR 141.71.
Accordingly, unfiltered PWSs must continue to comply with all existing
filtration avoidance criteria. EPA believes these criteria help to
ensure that watershed protection provides a microbial barrier in those
PWSs that do not filter.
Further, today's rule does not establish any new criteria for
filtration avoidance. In the proposed LT2ESWTR, EPA indicated that
compliance with DBP standards under the Stage 2 DBPR would be
incorporated into the criteria for filtration avoidance. However, EPA
has not done this in today's final rule in order to give States more
flexibility in working with unfiltered PWSs to comply with the Stage 2
DBPR.
3. Summary of Major Comments
EPA received significant public comment on the following treatment
requirements for unfiltered PWSs in the LT2ESWTR proposal: the
requirement for all unfiltered PWSs to provide at least 2-log
Cryptosporidium inactivation, treatment requirements for unfiltered
PWSs with high Cryptosporidium levels, and the requirement for
unfiltered PWSs to use at least two disinfectants. A summary of these
comments and EPA's responses follows.
Several commenters supported the requirement that all unfiltered
PWSs achieve at least 2-log inactivation of Cryptosporidium, noting
that this was part of the Agreement in Principle (USEPA 2000a). Some
commenters, however, requested that EPA not establish a minimum
Cryptosporidium treatment level due to the following factors:
monitoring of unfiltered PWS sources has shown very low levels of
Cryptosporidium, and some sources may have no Cryptosporidium; the
Cryptosporidium in an unfiltered PWS source are likely to be of non-
human origin and are less likely to infect humans; and disease
incidence data have not established a link between unfiltered PWSs and
cryptosporidiosis in consumers.
In response, EPA continues to believe that all unfiltered PWSs
should provide treatment for Cryptosporidium to protect public health.
Monitoring has shown that unfiltered PWS sources are contaminated with
Cryptosporidium, and no source is likely to be entirely free of
Cryptosporidium due to the ubiquity of Cryptosporidium in both human
and many animal populations. Studies, such as those cited in section
III, have established that Cryptosporidium from animals can infect
humans. EPA does not regard the absence of cryptosporidiosis cases
attributed to drinking water in a particular community as evidence that
no treatment for Cryptosporidium is needed. As described in section
III, cryptosporidiosis incidence data generally do not indicate overall
disease burden because most cases are undetected, unreported, and not
traced to a particular source.
Some commenters recommended that EPA require only 1-log
Cryptosporidium inactivation for unfiltered PWSs that demonstrate
source water levels below 0.001 oocysts/L. EPA does not support this
approach, though, due to concerns with the reliability of monitoring to
establish such an extremely low level of Cryptosporidium. In addition,
UV light is a feasible technology for unfiltered PWSs of all sizes to
achieve at least 2-log Cryptosporidium inactivation. For these reasons,
EPA has concluded that the minimum Cryptosporidium treatment level
should be 2-log, as recommended by the Advisory Committee.
In the proposed LT2ESWTR, EPA requested comment on the treatment
that should be required if an unfiltered PWS measured a Cryptosporidium
level of 0.075 oocysts/L or higher--the concentration at which a
filtered PWS must provide at least 4-log treatment. Several commenters
supported equivalent treatment requirements (i.e., at least 4-log
reduction) for unfiltered and filtered PWSs with Cryptosporidium at
this level. Other commenters stated that available data indicate no
unfiltered PWSs are likely to measure Cryptosporidium at such a high
level.
EPA agrees that available data on Cryptosporidium occurrence
suggest that no unfiltered PWSs will measure a mean level of 0.075
oocysts/L or higher. Moreover, establishing a 4-log treatment
requirement on the precautionary basis that an unfiltered PWS might
measure a high level of Cryptosporidium has a significant cost--it
would require any unfiltered PWS to provide 4-log, rather than 3-log,
inactivation to avoid Cryptosporidium monitoring. EPA expects that many
small unfiltered PWSs will choose to provide 3-log Cryptosporidium
inactivation rather than monitor for Cryptosporidium. Accordingly, EPA
has concluded that establishing a 4-log Cryptosporidium treatment
requirement for unfiltered PWSs that measure a Cryptosporidium level of
0.075 oocysts/L or higher is unnecessary and inappropriate at this
time. In the event that an unfiltered PWS does measure Cryptosporidium
at this level, the State can require the PWS to take steps to reduce
the contamination under existing watershed control program requirements
for unfiltered PWSs.
Some commenters supported the requirement for unfiltered PWSs to
use at least two disinfectants to meet overall inactivation
requirements for Cryptosporidium, Giardia lamblia, and viruses and for
each disinfectant to achieve the total inactivation required for one
target pathogen. These commenters stated that this requirement will
improve inactivation against a wide variety of pathogens and increase
treatment reliability. Other commenters, though, opposed this
requirement for a number of reasons: it will unnecessarily limit the
ability of PWSs to minimize DBPs, there is no similar requirement for
filtered PWSs, the requirement for each disinfectant to achieve the
total inactivation for one pathogen goes beyond the Agreement in
Principle, and EPA has not provided a risk analysis to justify the
requirement.

[[Page 684]]

In response, EPA believes that the benefits of both redundancy and
a broad spectrum of microbial protection justify requiring the use of
two disinfectants. Further, requiring each disinfectant to achieve the
full inactivation of one target pathogen establishes a minimal
performance level so that each disinfectant will serve as a substantive
barrier. In most cases, PWSs will comply with this requirement by using
UV or ozone to inactivate Giardia lamblia and Cryptosporidium and using
chlorine to inactivate viruses.

D. Options for Systems To Meet Cryptosporidium Treatment Requirements

1. Microbial Toolbox Overview
Today's rule includes a variety of treatment and control options,
collectively termed the ``microbial toolbox,'' that PWSs can implement
to comply with additional Cryptosporidium treatment requirements.
Options in the microbial toolbox include source protection and
management programs, prefiltration processes, treatment performance
programs, additional filtration components, and inactivation
technologies. The Stage 2 M-DBP Advisory Committee recommended the
microbial toolbox to provide PWSs with broad flexibility in selecting
cost-effective LT2ESWTR compliance strategies.
Most options in the microbial toolbox carry prescribed credits
toward Cryptosporidium treatment requirements. PWSs receive these
credits by demonstrating compliance with required design and
operational criteria, which are described in the sections that follow.
In addition, States may award treatment credits other than the
prescribed credit through a ``demonstration of performance,'' which
involves site-specific testing by a PWS with a State-approved protocol.
Under a demonstration of performance, a State may award credit to a
treatment plant or to a unit process of a treatment plant that is
higher or lower than the prescribed credit. This option also allows
States to award credit to a unit process that does not meet the design
and operational criteria in the microbial toolbox for prescribed credit.
To be eligible for treatment credit for a microbial toolbox option,
PWSs must initially report compliance with design criteria, where
required, to the State (some options do not require design criteria).
Thereafter, for most options, PWSs must report compliance with required
operational criteria to the State each month (the watershed control
program option requires yearly reporting). Failure by a PWS in any
month to demonstrate treatment credit equal to or greater than its
Cryptosporidium treatment requirements under today's rule is a
treatment technique violation. This violation lasts until the PWS
demonstrates that it is meeting criteria for sufficient treatment
credit to satisfy its Cryptosporidium treatment requirements.
As described in section IV.B, filtered PWSs may use any option or
combination of options from the microbial toolbox to comply with the
additional Cryptosporidium treatment requirements of Bin 2. PWSs in
Bins 3 or 4 must achieve at least 1-log of the additional
Cryptosporidium treatment requirement by using ozone, chlorine dioxide,
UV, membranes, bag filtration, cartridge filtration, or bank filtration.
If allowed by the State, PWSs may use different microbial toolbox
options in different months to comply with Cryptosporidium treatment
requirements under today's rule. For example, a PWS in Bin 2, which
requires 1-log additional Cryptosporidium treatment, could comply with
this requirement in one month using ``individual filter performance,''
which carries a 1-log credit; in a subsequent month, this PWS could use
``combined filter performance'' and ``presedimentation basin with
coagulation,'' which each carry 0.5-log credit. This approach is
intended to provide greater operational flexibility to PWSs. It allows
a PWS to receive treatment credit for a microbial toolbox option in any
month the PWS is able to meet required operational criteria, even if
the PWS does not meet these criteria during all months of the year.
Table IV.D-1 summarizes prescribed treatment credits and associated
design and operational criteria for microbial toolbox options. The
sections that follow describe each toolbox option in detail. In
addition, EPA has developed three guidance documents to assist PWSs
with selecting and implementing microbial toolbox options: Toolbox
Guidance Manual, UV Disinfection Guidance Manual, and Membrane
Filtration Guidance Manual. Each may be acquired from EPA's Safe
Drinking Water Hotline, which can be contacted as described under FOR
FURTHER INFORMATION CONTACT at the beginning of this notice.

Table IV.D-1.--Microbial Toolbox: Options, Credits and Criteria
------------------------------------------------------------------------
Cryptosporidium treatment credit
Toolbox option with design and operational criteria
\1\
------------------------------------------------------------------------
Source Protection and Management Toolbox Options
------------------------------------------------------------------------
Watershed control program......... 0.5-log credit for State-approved
program comprising required
elements, annual program status
report to State, and regular
watershed survey. Unfiltered PWSs
are not eligible for credit.
Alternative source/intake No prescribed credit. PWSs may
management. conduct simultaneous monitoring for
treatment bin classification at
alternative intake locations or
under alternative intake management
strategies.
-----------------------------------
Prefiltration Toolbox Options
------------------------------------------------------------------------
Presedimentation basin with 0.5-log credit during any month that
coagulation. presedimentation basins achieve a
monthly mean reduction of 0.5-log
or greater in turbidity or
alternative State-approved
performance criteria. To be
eligible, basins must be operated
continuously with coagulant
addition and all plant flow must
pass through basins.
Two-stage lime softening.......... 0.5-log credit for two-stage
softening where chemical addition
and hardness precipitation occur in
both stages. All plant flow must
pass through both stages. Single-
stage softening is credited as
equivalent to conventional
treatment.
Bank filtration................... 0.5-log credit for 25-foot setback;
1.0-log credit for 50-foot setback;
horizontal and vertical wells only;
aquifer must be unconsolidated sand
containing at least 10 percent
fines (as defined in rule); average
turbidity in wells must be less
than 1 NTU. PWSs using existing
wells followed by filtration must
monitor the well effluent to
determine bin classification and
are not eligible for additional
credit.
-----------------------------------

[[Page 685]]

Treatment Performance Toolbox Options
------------------------------------------------------------------------
Combined filter performance....... 0.5-log credit for combined filter
effluent turbidity less than or
equal to 0.15 NTU in at least 95
percent of measurements each month.
Individual filter performance..... 0.5-log credit (in addition to 0.5-
log combined filter performance
credit) if individual filter
effluent turbidity is less than or
equal to 0.15 NTU in at least 95
percent of samples each month in
each filter and is never greater
than 0.3 NTU in two consecutive
measurements in any filter.
Demonstration of performance...... Credit awarded to unit process or
treatment train based on a
demonstration to the State with a
State-approved protocol.
-----------------------------------
Additional Filtration Toolbox Options
------------------------------------------------------------------------
Bag and cartridge filters......... Up to 2-log credit with
demonstration of at least 1-log
greater removal in a challenge test
when used singly. Up to 2.5-log
credit with demonstration of at
least 0.5-log greater removal in a
challenge test when used in series.
Membrane filtration............... Log credit equivalent to removal
efficiency demonstrated in
challenge test for device if
supported by direct integrity
testing.
Second stage filtration........... 0.5-log credit for second separate
granular media filtration stage if
treatment train includes
coagulation prior to first filter.
Slow sand filters................. 2.5-log credit as a secondary
filtration step; 3.0-log credit as
a primary filtration process. No
prior chlorination.
-----------------------------------
Inactivation Toolbox Options
------------------------------------------------------------------------
Chlorine dioxide.................. Log credit based on measured CT in
relation to CT table.
Ozone............................. Log credit based on measured CT in
relation to CT table.
UV................................ Log credit based on validated UV
dose in relation to UV dose table;
reactor validation testing required
to establish UV dose and associated
operating conditions.
------------------------------------------------------------------------
\1\ Table provides summary information only; refer to following preamble
and regulatory language for detailed requirements.

2. Watershed Control Program

a. Today's Rule
Filtered PWSs can receive 0.5-log credit toward Cryptosporidium
treatment requirements under today's rule for implementing a State-
approved watershed control program designed to reduce the level of
Cryptosporidium. To be eligible to receive this credit initially, PWSs
must perform the following steps:
? Notify the State of the intent to develop a new or
continue an existing watershed control program for Cryptosporidium
treatment credit no later than two years prior to the date the PWS must
comply with additional Cryptosporidium treatment requirements under
today's rule.
? Submit a proposed watershed control plan to the State for
approval no later than one year prior to the date the PWS must comply
with additional Cryptosporidium treatment requirements under today's
rule. The watershed control plan must contain these elements:
(1) The designation of an ``area of influence'' in the watershed,
which is defined as the area outside of which the likelihood of
Cryptosporidium contamination affecting the treatment plant intake is
not significant;
(2) The identification of both potential and actual sources of
Cryptosporidium contamination, including a qualitative assessment of
the relative impact of these contamination sources on water quality at
the treatment plant intake;
(3) An analysis of control measures that could mitigate the sources
of Cryptosporidium contamination, including the relative effectiveness
of control measures in reducing Cryptosporidium loading to the source
water and their feasibility; and
(4) A statement of goals and specific actions the PWS will
undertake to reduce source water Cryptosporidium levels, including a
description of how the actions will contribute to specific goals,
watershed partners and their roles, resource requirements and
commitments, and a schedule for plan implementation.
If the State approves the watershed control plan for
Cryptosporidium treatment credit, PWSs must perform the following steps
to be eligible to maintain the credit:
? Submit an annual watershed control program status report
to the State no later than a date specified by the State. The status
report must describe the following: (1) how the PWS is implementing the
approved watershed control plan; (2) the adequacy of the plan to meet
its goals; (3) how the PWS is addressing any shortcomings in plan
implementation; and (4) any significant changes that have occurred in
the watershed since the last watershed sanitary survey.
? Notify the State prior to making any significant changes
to the approved watershed control plan. If any change is likely to
reduce the planned level of source water protection, the PWS must
include in this notification a statement of actions that will be taken
to mitigate this effect.
? Perform a watershed sanitary survey no less frequently
than the PWS must undergo a sanitary survey under 40 CFR
142.16(b)(3)(i), which is every three to five years, and submit the
survey report to the State for approval. The State may require a PWS to
perform a watershed sanitary survey at an earlier date if the State
determines that significant changes may have occurred in the watershed
since the previous sanitary survey. A person approved by the State must
conduct the watershed sanitary survey and the survey must meet
applicable State guidelines. The watershed sanitary survey must
encompass the area of influence as identified in the State-approved
watershed control plan, assess the implementation of actions to reduce
source water Cryptosporidium levels, and identify any significant new
sources of Cryptosporidium.
PWSs are eligible to receive Cryptosporidium treatment credit under
today's rule for preexisting watershed control programs (e.g., programs
in place at the time of rule promulgation).

[[Page 686]]

To be eligible for credit, such programs must meet the requirements
stated in this section and the watershed control plan must address
future actions that will further reduce source water Cryptosporidium
levels.
If the State determines that a PWS is not implementing the approved
watershed control plan (i.e., the PWS is not carrying out the actions
on the schedule in the approved plan), the State may revoke the
Cryptosporidium treatment credit for the watershed control program.
Failure by a PWS to demonstrate treatment credit at least equal to its
Cryptosporidium treatment requirement under today's rule due to such a
revocation of credit is a treatment technique violation. The violation
lasts until the State determines that the PWS is implementing an
approved watershed control plan or is otherwise achieving the required
level of Cryptosporidium treatment credit.
PWSs must make the approved watershed control plan, annual status
reports, and watershed sanitary surveys available to the public upon
request. These documents must be in a plain language style and include
criteria by which to evaluate the success of the program in achieving
plan goals. If approved by the State, the PWS may withhold portions of
these documents based on security considerations.
Unfiltered PWSs are not eligible to receive Cryptosporidium
treatment credit for a watershed control program under today's rule.
Under existing regulations (40 CFR 141.71), unfiltered PWSs must
maintain a watershed control program that minimizes the potential for
contamination by Cryptosporidium as a condition for avoiding filtration.

b. Background and Analysis

Cryptosporidium enters drinking water through fecal contamination
of PWS source waters. Implementing a watershed control program that
reduces or treats sources of fecal contamination in PWS sources will
benefit public health by lowering the exposure of drinking water
consumers to Cryptosporidium and other pathogenic microorganisms. In
addition, a watershed control program may enhance treatment plant
management practices through generating knowledge of the sources, fate,
and transport of pathogens.
The Stage 2 M-DBP Advisory Committee recommended 0.5-log
Cryptosporidium treatment credit for a watershed control program (USEPA
2000a), and the August 11, 2003 proposal included criteria for PWSs to
receive this credit (USEPA 2003a). The following discussion summarizes
the basis for this credit and for differences in associated
requirements between the proposal and today's final rule.
The efficacy of a watershed control program in reducing levels of
Cryptosporidium and other microbial pathogens depends on the ability of
a PWS to identify and control sources of fecal contamination. The fecal
sources that are significant in a particular watershed and the control
measures that will be effective in mitigating these sources are site
specific. Consequently, EPA believes that States should determine
whether a watershed control program developed by a PWS to reduce
Cryptosporidium contamination warrants 0.5-log treatment credit.
Accordingly, today's rule requires State approval of watershed control
programs for PWSs to receive credit.
If a PWS intends to implement a watershed control program to comply
with Cryptosporidium treatment requirements under today's rule, EPA
believes the PWS should notify the State at least two years prior to
the required treatment compliance date. This notification will give the
State an opportunity to communicate with the PWS regarding site-
specific considerations for a watershed control program. Further, the
PWS should submit the proposed watershed control plan to the State for
approval at least one year prior to the treatment compliance date. This
schedule will give the State time to evaluate the program for approval
and, if necessary, allow the PWS to make modifications necessary for
approval. Thus, today's rule establishes these reporting deadlines.
The required elements for a watershed control plan in today's rule
are the minimum necessary for a program that will be effective in
reducing levels of Cryptosporidium and other pathogens in a treatment
plant intake. These elements include defining the area of the watershed
where contamination can affect the intake water quality, identifying
sources of contamination within this area, evaluating control measures
to reduce contamination, and developing an action plan to implement
specific control measures.
EPA encourages PWSs to leverage other Federal, State, and local
programs in developing the elements of their watershed control plans.
For example, SDWA section 1453 requires States to carry out a source
water assessment program (SWAP) for PWSs. Depending on how a State
implements this program, the SWAP may be used to define the area of
influence in the watershed and identify actual and potential
contamination sources. In 2002, EPA launched the Watershed Initiative
(67 FR 36172, May 23, 2002) (USEPA 2002b), which will provide grants to
support watershed-based approaches to preventing, reducing, and
eliminating water pollution. In addition, EPA recently promulgated
regulations for Concentrated Animal Feeding Operations that will limit
discharges that contribute microbial pathogens to watersheds.
Many PWSs do not control the watersheds of their sources of supply.
Their watershed control plans should involve partnerships with
watershed landowners and government agencies that have authority over
activities in the watershed that may contribute Cryptosporidium to the
water supply. Stakeholders that control activities that could
contribute to Cryptosporidium contamination include municipal
government and private operators of wastewater treatment plants,
livestock farmers and persons who spread manure, individuals with
failing septic systems, logging operations, and other government and
commercial organizations.
After a State approves a watershed control plan for a PWS and
initially awards 0.5-log Cryptosporidium treatment credit, the PWS must
submit a watershed control program status report to the State each
year. These reports are required for States to exercise oversight and
ensure that PWSs implement the approved watershed control plan. They
also provide a mechanism for PWSs to work with the States to address
any shortcomings or necessary modifications in watershed control plans
that are identified after plan approval.
In addition, PWSs must undergo watershed sanitary surveys every
three to five years by a State-approved party. These surveys will
provide information to PWSs and States regarding significant changes in
the watershed that may warrant modification of the approved watershed
control plan. Also, they allow for an assessment of watershed control
plan implementation.
The proposed rule required watershed sanitary surveys annually, but
EPA has reduced the frequency to every three to five years in today's
final rule. This frequency is consistent with existing requirements for
PWS sanitary surveys. EPA is establishing this longer frequency on the
basis that most watersheds will not undergo significant changes over
the course of a single year. If significant changes in the watershed do
occur, however, PWSs must identify these changes in their annual
program status reports. In addition, States have

[[Page 687]]

the authority to require that a watershed sanitary survey be conducted
at an earlier date if the State determines that significant changes may
have occurred in the watershed since the previous survey.
In the proposed rule, approval of a watershed control program
expired after a PWS completed the second round of source water
monitoring, and the PWS had to reapply for program approval. Today's
final rule, however, does not include this requirement. Instead,
today's rule gives States authority to revoke Cryptosporidium treatment
credit for a watershed control program at any point if a State
determines that a PWS is not implementing the approved watershed
control plan. EPA believes this approach is preferable to the automatic
expiration of credit in the proposed rule for two reasons: (1) It
assures PWSs that if they implement the approved watershed control
plan, they will maintain the treatment credit; and (2) it gives States
the authority to ensure PWSs implement watershed control programs for
which they receive treatment credit and to take action at any time if a
PWS does not.
EPA believes that PWSs should be eligible to receive
Cryptosporidium treatment credit for watershed control programs that
are in place prior to the treatment compliance date. The same
requirements for watershed control program treatment credit apply
regardless of whether the program is new or existing at the time the
PWS submits the watershed control plan for approval. In the case of
existing programs, the watershed control plan must list future activities
the PWS will undertake that will reduce source water contamination.
The Toolbox Guidance Manual lists programmatic resources and
guidance available to assist PWSs in building partnerships and
implementing watershed protection activities. It also incorporates
information on the effectiveness of different control measures to
reduce Cryptosporidium levels and provides case studies of watershed
control programs. This guidance is intended to assist both PWSs in
developing watershed control programs and States in assessing and
approving these programs.
In addition to this guidance and other technical resources, EPA
provides funding for watershed and source water protection through the
Drinking Water State Revolving Fund (DWSRF) and Clean Water State
Revolving Fund (DWSRF). Under the DWSRF program, States may fund source
water protection activities by PWSs, including watershed management and
pathogen source reduction plans. CWSRF funds can be used for
agricultural best management practices to reduce pathogen loading in
receiving waters and for the replacement of failing septic systems.

c. Summary of Major Comments

Public comments on the August 11, 2003, LT2ESWTR proposal supported
the concept of awarding credit towards Cryptosporidium treatment
requirements for an effective watershed control program. Commenters
expressed concerns, however, with specific criteria for awarding this
credit, including annual watershed sanitary surveys, re-approval of
watershed control programs, standards for existing watershed control
programs, and public availability of documents related to the watershed
control program. A summary of these comments and EPA's responses follows.
Regarding the proposed requirement for annual watershed sanitary
surveys, commenters stated that this frequency is too high because
activities to reduce Cryptosporidium contamination in the watershed
will often take many years to implement. These commenters recommended
that watershed sanitary surveys be performed every three to five years
in conjunction with PWSs sanitary surveys or longer. In contrast, other
commenters supported annual watershed sanitary surveys as being
necessary to allow proper responses to new sources of contamination
that can occur quickly in watersheds. Such sources can occur through
development, new recreation programs, fires, unauthorized activities,
and other factors.
While EPA believes that regular watershed sanitary surveys are
necessary to identify new sources of contamination and allow States to
properly oversee watershed control programs, EPA agrees that
significant changes typically will not occur over one year. Therefore,
today's final rule requires PWSs that receive Cryptosporidium treatment
credit for a watershed control program to undergo watershed sanitary
surveys every three to five years, rather than every year. To address
the concern that new sources of watershed contamination can arise
quickly, today's rule requires PWSs to identify any significant changes
that have occurred in their watersheds in their annual program status
reports. States can then require a watershed sanitary survey at an earlier
date if significant changes have occurred since the previous survey.
Many commenters opposed the proposed requirement for PWSs to
reapply for approval of their watershed control programs after
completing the second round of source water monitoring. The concern was
that this requirement would discourage PWSs from pursuing watershed
control programs because they would be uncertain about whether they
would continue to receive treatment credit for their programs in the
future. As an alternative, commenters recommended that States monitor
the progress of PWSs in implementing watershed control programs through
the watershed sanitary surveys and annual status reports. A State could
then deny treatment credit to a PWS if it failed to demonstrate
adequate commitment to its approved watershed control plan.
EPA agrees with these comments and today's final rule does not
include a requirement for re-approval of the watershed control program
after the second round of monitoring. Instead, PWSs must submit annual
program status reports to the State and undergo regular watershed
sanitary surveys. If the State determines that a PWS is not
implementing its approved watershed control plan on the basis of these
measures, it can withdraw the treatment credit associated with the
program. PWSs that implement their approved watershed control plans,
however, can maintain the associated treatment credit indefinitely
under today's rule.
Several commenters stated that PWSs with existing watershed control
programs should be eligible for Cryptosporidium treatment credit under
the same standards that apply to new programs. EPA agrees that both
existing and new watershed control programs should be eligible for
Cryptosporidium treatment credit under the same standards, and today's
rule allows this. As is required for new programs, PWSs with existing
watershed control programs must submit a watershed control plan that
details future activities the PWS will implement to reduce source water
contamination. As with new programs, States will have the discretion to
approve the proposed watershed control plan for 0.5-log Cryptosporidium
treatment credit.
With respect to a proposed requirement that the watershed control
plan, annual status reports, and watershed sanitary surveys be made
available to the public, commenters stated that homeland security
concerns are associated with these documents. Homeland security
concerns apply to information on the location of treatment plant
intakes and other structures. EPA agrees that there are security
concerns associated with watershed control program documents. EPA also
believes, though, that the public should be allowed to learn about the
actions PWSs

[[Page 688]]

plan to take to address Cryptosporidium contamination and the progress
of PWSs in implementing these actions. Consequently, today's rule
requires PWSs to make the approved watershed control plan, annual
status reports, and watershed sanitary surveys available to the public.
However, PWSs may withhold portions of these documents that raise
security concerns with State approval.
3. Alternative Source
a. Today's Rule
If approved by the State, a PWS may determine its Cryptosporidium
treatment requirements under today's rule using additional source water
monitoring results for an alternative treatment plant intake location
or an alternative intake operational strategy. By meeting the
requirements of this option, which are described as follows, a PWS may
reduce its Cryptosporidium treatment requirements under today's rule.
? Monitoring for an alternative intake location or
operational strategy, termed ``alternative source monitoring,'' may
only be performed in addition to monitoring the existing plant
intake(s) (i.e., the intake(s) the PWS uses when it must begin
monitoring under today's rule).
? Alternative source monitoring must meet the sample number,
sample frequency, and data quality requirements that apply to source
water monitoring for bin classification, as described in section IV.A.
? PWSs that perform alternative source monitoring must
complete this monitoring by the applicable deadline for treatment bin
classification under today's rule, as described in section IV.G. Unless
a PWS grandfathers monitoring data for the existing plant intake,
alternative source monitoring must be performed concurrently with
monitoring the existing intake.
? PWSs must submit the results of alternative source
monitoring to the State, along with supporting information documenting
the location and/or operating conditions under which the alternative
source monitoring was conducted. If a PWS fulfills these requirements,
the PWS may request that the State classify the PWS in a treatment bin
under today's rule using the alternative source monitoring results.
? If the State approves bin classification for a PWS using
alternative source monitoring results, the PWS must relocate the plant
intake or implement the intake operational strategy to reflect the
alternative source monitoring. The PWS must complete these actions no
later than the applicable date for the PWS to comply with
Cryptosporidium treatment requirements under today's rule. The State
may specify reporting requirements to verify operational practices.
Failure by a PWS that is classified in a treatment bin using
alternative source monitoring to relocate the intake or implement the
new intake operational strategy, as required, by the applicable
treatment compliance deadline is a treatment technique violation. This
violation lasts until the State determines that the PWS has carried out
required changes to the intake location or operation or is providing
the level of Cryptosporidium treatment required for the existing intake
location and operation.
b. Background and Analysis
Plant intake refers to the works or structures at the head of a
conduit through which water is diverted from a source (e.g., river or
lake) into a treatment plant. Plants may be able to reduce influent
Cryptosporidium levels by changing the intake placement (either within
the same source or to an alternate source) or managing the timing or
level of withdrawal.
The Stage 2 M-DBP Advisory Committee recommended that PWSs be
allowed to modify their plant intakes to comply with today's rule, and
the August 11, 2003 proposal included this option (USEPA 2000a). The
requirements for this option in today's final rule are unchanged from
the proposal. The following discussion summarizes the basis for these
requirements.
The effect of changing the location or operation of a plant intake
on influent Cryptosporidium levels can only be ascertained through
monitoring. Consequently, EPA is not establishing a prescriptive credit
for this option. Rather, if a PWS expects that Cryptosporidium levels
from a current plant intake will result in a bin classification
requiring additional treatment under today's rule, the PWS may conduct
additional Cryptosporidium monitoring reflecting a different intake
location or operational strategy (alternative source monitoring). The
PWS may then request that the State approve bin classification for the
plant based on alternative source monitoring results, provided the PWS
will implement the corresponding changes to the intake location or
operation.
PWSs that conduct alternative source monitoring must also monitor
their existing plant intakes. Monitoring the existing intake is
required for the State to determine a treatment bin classification for
a plant in the event the PWS does not modify the intake (to reflect
alternative source monitoring) prior to the treatment compliance
deadline under today's rule.
Further, PWSs must conduct alternative source monitoring within the
applicable time frame for source water monitoring under today's rule.
This approach is required for the State to determine a bin
classification for the plant based on alternative source monitoring by
the bin classification deadline. In addition, this timing will allow
the PWS to modify the intake or implement additional treatment, if
necessary, by the treatment compliance deadline. This requirement
means, however, that unless a PWS meets the requirement for monitoring
its existing intake through grandfathering, the PWS must perform
alternative source monitoring concurrently with existing intake
monitoring, although it does not have to be on exactly the same schedule.
Because alternative source monitoring will be used for bin
classification, this monitoring must comply with all applicable
requirements for source water monitoring that are described in section
IV.A. Further, the PWS must provide the State with supporting
information documenting the conditions, such as the source location,
under which the alternative source monitoring was conducted. This
documentation is required so that if bin classification is based on
alternative source monitoring results, the State can ensure the PWS
implements the corresponding modifications to the intake.
c. Summary of Major Comments
Public comments on the August 11, 2003, LT2ESWTR proposal supported
allowing PWSs to determine treatment bin classification by monitoring
for an alternative intake location or operational strategy. Several
commenters stated they were unsure if this option would be widely used
due to the burden of performing Cryptosporidium monitoring at both the
current intake and the alternative source. Commenters also recommended
that PWSs first conduct source water assessments or watershed sanitary
surveys to evaluate intake management strategies to reduce
Cryptosporidium levels in the plant influent.
In response, EPA believes that PWSs who choose alternative source
monitoring must also monitor their current intake so that the State can
determine the appropriate bin classification if the PWS does not

[[Page 689]]

subsequently modify its intake. While few PWSs may choose to pursue
alternative source monitoring, EPA believes this option should be
available for PWSs that elect to do so. EPA agrees that it is
appropriate for PWSs to assess contamination sources in the watershed
when considering whether to relocate or change the operation of their
intakes. The Toolbox Guidance Manual provides direction to PWSs on
conducting these assessments.
EPA requested comment on whether representative Cryptosporidium
monitoring can be performed prior to implementation of a new intake
strategy (e.g., monitoring a new source prior to constructing a new
intake structure). Commenters stated that there may be situations where
allowing Cryptosporidium monitoring to demonstrate a reduction in
oocyst levels prior to implementation of a new intake strategy is
appropriate. Incurring costs for constructing a new intake before
determining whether the strategy will reduce oocyst levels is not cost
effective. EPA agrees with this comment and today's rule allows PWSs to
conduct alternative source monitoring prior to constructing a new
intake and to base their bin classification on these monitoring results
with State approval.
4. Pre-Sedimentation With Coagulant
a. Today's Rule
Presedimentation is a preliminary treatment process used to remove
gravel, sand and other particulate material from the source water
through settling before the water enters the primary clarification and
filtration processes in a treatment plant. PWSs receive 0.5-log credit
towards Cryptosporidium treatment requirements under today's rule for a
presedimentation process that meets the following conditions:
? Treats all flow reaching the treatment plant;
? Continuously adds a coagulant to the presedimentation basin;
? Achieves one of the following two performance criteria:
(1) Demonstrates at least 0.5-log mean reduction of influent
turbidity. This reduction must be determined using daily turbidity
measurements in the presedimentation process influent and effluent and
must be calculated as follows: log₁₀ (monthly mean of daily
influent turbidity)--log₁₀ (monthly mean of daily effluent
turbidity).
(2) Complies with State-approved performance criteria that
demonstrate at least 0.5-log mean removal of micron-sized particulate
material, such as aerobic spores, through the presedimentation process.
PWSs may receive treatment credit for a presedimentation process
during any month the process meets these conditions. To be eligible for
credit, PWSs must report compliance with these conditions to the State
each month. PWSs may earn presedimentation treatment credit for only
part of the year if the process does not meet these conditions year-
round. In this situation, PWSs must fully meet their Cryptosporidium
treatment requirements under today's rule using other microbial toolbox
options during those months when the PWS does not receive treatment
credit for presedimentation.
Alternatively, PWSs may apply to the State for Cryptosporidium
treatment credit for presedimentation processes using a demonstration
of performance, as described in section IV.D.9. Demonstration of
performance provides an option for PWSs with presedimentation processes
that do not meet these prescribed conditions for treatment credit and
for PWSs who seek greater than 0.5-log Cryptosporidium treatment credit
for their presedimentation processes.
PWSs are not eligible for Cryptosporidium treatment credit for a
presedimentation process if their sampling point for the source water
Cryptosporidium monitoring used for bin classification was after (i.e.,
downstream of) the presedimentation process. In this case, the removal
achieved by the presedimentation process will be reflected in the
monitoring results and bin classification.
b. Background and Analysis
Presedimentation involves passing raw water through retention
basins in which particulate material is removed through settling. PWSs
use presedimentation to reduce and stabilize particle concentrations
prior to the primary clarification and filtration processes in a
treatment plant. Presedimentation is often operated at higher hydraulic
overflow rates than conventional sedimentation (the sedimentation
process that directly precedes filtration in a conventional treatment
plant) and may not involve coagulant addition. PWSs may operate a
presedimentation process only during periods of high raw water turbidity.
As a process for removing particles, presedimentation can reduce
Cryptosporidium levels to some degree. In addition, presedimentation
can improve the performance of subsequent treatment processes by
dampening variability in raw water quality. The efficacy of
presedimentation in removing particles, including Cryptosporidium, is
influenced by the use of coagulant, the hydraulic loading rate, water
quality parameters like temperature and turbidity, and physical
characteristics of the sedimentation basin.
The Stage 2 M-DBP Advisory Committee recommended 0.5-log
Cryptosporidium treatment credit for presedimentation with coagulation
(USEPA 2000a). The August 11, 2003 proposal included criteria, which
were similar to those in today's final rule, for PWSs to receive this
credit (USEPA 2003a). The following discussion summarizes the basis for
this credit and for differences in associated requirements between the
proposal and today's final rule.
In the proposal, EPA reviewed published studies of Cryptosporidium
removal through conventional sedimentation processes by Payment and
Franco (1993), Kelly et al. (1995), Patania et al. (1995), States et
al. (1997), Edzwald and Kelly (1998), and Dugan et al. (2001). These
studies included bench-, pilot-, and full-scale processes, and the
reported levels of Cryptosporidium removal varied widely, ranging from
0.4- to 3.8-log. In addition, these studies also supported two other
significant findings:

(1) Proper coagulation significantly improves Cryptosporidium
removal through sedimentation. In Dugan et al. (2001), for example,
average Cryptosporidium removal across a sedimentation basin was
1.3-log with optimal coagulation and decreased to 0.2-log when the
coagulant dose was insufficient.
(2) The removal of aerobic spores correlates well with the
removal of Cryptosporidium when a coagulant is present. This
indicates that aerobic spores, which are naturally present in
surface waters, may be used as an indicator of Cryptosporidium
removal in coagulated full-scale sedimentation processes.

Cryptosporidium removal efficiencies in conventional sedimentation
may be higher than in presedimentation due to differences in hydraulic
loading rates, coagulant doses, and other factors. EPA identified no
published studies of Cryptosporidium removal through presedimentation
processes. In the proposal, however, EPA evaluated data on the removal
of aerobic spores in the presedimentation processes of three PWSs as an
indicator of Cryptosporidium removal (USEPA 2003a). All three PWSs
added a coagulant (polymer, metal salts, or recycled sludge) to the
presedimentation process. The mean removal of aerobic spores through
presedimentation in the three PWSs ranged from 0.5- to 1.1-log over time

[[Page 690]]

spans ranging from several months to several years.
These data support the finding that full-scale presedimentation
processes can achieve Cryptosporidium removals of 0.5-log and greater
under routine operating conditions and over an extended time period.
Accordingly, EPA concluded that 0.5-log Cryptosporidium treatment
credit for presedimentation processes is appropriate under certain
conditions. Today's rule establishes three conditions for PWSs to
receive this credit.
The first condition for presedimentation to receive 0.5-log
Cryptosporidium treatment credit is that the process must treat all
flow reaching the treatment plant. Presedimentation cannot reduce the
Cryptosporidium level entering a treatment plant by 0.5-log or greater
on a continuous basis if the process is operated intermittently or
treats only a fraction of the plant flow. EPA recognizes that for some
PWSs, operating a presedimentation process intermittently in response
to high turbidity levels is preferable to continuous operation. By
establishing a requirement for continuous operation as a condition for
treatment credit, EPA is not recommending against intermittent
operation of presedimentation processes. Rather, EPA is only
identifying one of the conditions under which a 0.5-log Cryptosporidium
treatment credit for presedimentation appears to be justified.
A second condition for presedimentation treatment credit is that
the process must operate with coagulant addition. Available data
support awarding 0.5-log Cryptosporidium treatment credit to a
presedimentation process only when a coagulant is present. The full-
scale presedimentation data reviewed in the proposal involved coagulant
addition, and literature studies indicate that Cryptosporidium removal
through sedimentation can be substantially lower in the absence of
sufficient coagulant. Further, the Stage 2 M-DBP Advisory Committee
specifically recommended 0.5-log Cryptosporidium treatment credit for
presedimentation with coagulation (USEPA 2000a). Based on these
factors, EPA concluded that coagulation is a necessary condition for
PWSs to receive treatment credit for presedimentation.
The third condition for awarding treatment credit to
presedimentation is that the process must achieve a monthly mean
turbidity reduction of at least 0.5-log or meet alternative State-
approved performance criteria. This requirement stems from a
recommendation by the SAB, which reviewed data for awarding treatment
credit to presedimentation under the LT2ESWTR. In their report, the SAB
concluded that available data were minimal to support 0.5-log
prescribed credit for presedimentation and recommended that performance
criteria other than overflow rate be included if credit is given for
presedimentation (SAB 2003).
In response to this recommendation by the SAB, EPA analyzed the
relationship between removal of aerobic spores (as an indicator of
Cryptosporidium removal) and reduction in turbidity in the full-scale
presedimentation processes of three PWSs. The results of this analysis,
which are shown in Table IV.D-2, suggest that presedimentation
processes achieving a monthly mean reduction in turbidity of at least
0.5-log have a high likelihood of reducing mean Cryptosporidium levels
by 0.5-log or more. Consequently, EPA concluded that turbidity
reduction is an appropriate performance criterion for awarding
Cryptosporidium treatment credit to presedimentation basins. The Agency
believes this performance criterion addresses the concern raised by the
SAB.

Table IV.D-2.--Relationship Between Mean Turbidity Reduction and the
Percent of Months When Mean Spore Removal Was at Least 0.5 Log
------------------------------------------------------------------------
Percent of
months with at
least 0.5 Log
Log reduction in turbidity (monthly mean) Mean Reduction
in spores
(percent)
------------------------------------------------------------------------
at least 0.1-log........................................ 64
at least 0.2-log........................................ 68
at least 0.3-log........................................ 73
at least 0.4-log........................................ 78
at least 0.5-log........................................ 89
at least 0.6-log........................................ 91
at least 0.7-log........................................ 90
at least 0.8-log........................................ 89
at least 0.9-log........................................ 95
at least 1.0-log........................................ 96
------------------------------------------------------------------------
Source: Data from Cincinnati Water Works, Kansas City Water Services
Department, and St. Louis Water Division.

The proposed rule required PWSs to achieve at least 0.5-log
turbidity reduction through presedimentation in at least 11 of the 12
previous consecutive months to be eligible for presedimentation
treatment credit. EPA recognizes, however, that some PWSs will not be
able to demonstrate at least 0.5-log turbidity reduction through
presedimentation during months when raw water turbidity is lower. As a
result, these PWSs would not be able to achieve treatment credit for
their presedimentation basins. To provide more options for these PWSs,
EPA has modified this requirement in today's final rule in two respects.
The first modification is that in today's final rule, PWSs must
demonstrate compliance with the conditions for presedimentation
treatment credit on a monthly, rather that a yearly basis. This
requirement allows treatment credit for presedimentation in any month a
PWS can demonstrate at least 0.5-log turbidity reduction, even if the
PWS cannot achieve this level of turbidity reduction in all months of
the year.
A PWS that meets the conditions for presedimentation treatment
credit for only part of the year must implement other microbial toolbox
options to comply with Cryptosporidium treatment requirements in the
remainder of the year. Nevertheless, achieving presedimentation
treatment credit for even part of the year may benefit certain PWSs.
For example, a PWS may be able to reduce the level of disinfection it
provides during the months it receives presedimentation treatment
credit, or this treatment credit may provide a margin of safety to
ensure compliance with Cryptosporidium treatment requirements.
The second modification is the allowance for States to approve
alternative performance criteria to turbidity reduction that
demonstrate at least 0.5-log mean removal of micron-sized particulate
material through the presedimentation process. EPA believes that
aerobic spores are an appropriate alternative criterion. As described
earlier, studies support the use of aerobic spores as an indicator of
Cryptosporidium removal in coagulated sedimentation processes. If
approved by the State, a PWS could receive 0.5-log treatment credit for
presedimentation by demonstrating at least 0.5-log reduction in aerobic
spores. The Toolbox Guidance Manual provides information on analytical
methods for measuring aerobic spores. This may provide an option for
PWSs that are not able to demonstrate 0.5-log turbidity reduction but
have a sufficient concentration of aerobic spores in their raw water.
PWSs may work with States to identify other alternative criteria, as
well as appropriate monitoring to support use of the criteria.
c. Summary of Major Comments
Public comments on the August 11, 2003, LT2ESWTR proposal supported
allowing PWSs to achieve 0.5-log credit towards Cryptosporidium
treatment requirements for presedimentation with

[[Page 691]]

coagulation. Some commenters also supported the proposed operational,
monitoring, and performance conditions required for PWSs to receive
this credit. Other commenters, however, opposed the proposed
requirement for turbidity reduction as a condition for receiving
presedimentation treatment credit. A summary of these commenters'
concerns and EPA's responses follows.
Commenters who opposed requiring turbidity reduction for
presedimentation treatment credit were concerned that PWSs cannot
achieve this criterion during periods when raw water turbidity is low.
Further, these commenters stated that turbidity removal does not
reflect the overall benefits of presedimentation, which improves the
performance of the primary treatment train by equalizing water quality.
Some commenters also provided data showing the reduction in turbidity
and aerobic spore levels in the presedimentation processes of several
PWSs and stated that turbidity removal may not be an appropriate
indicator of acceptable performance for presedimentation basins.
Several commenters suggested that EPA establish a limit on hydraulic
overflow rate in place of a turbidity removal requirement.
In response, EPA continues to believes that 0.5-log turbidity
reduction is an appropriate performance indicator for 0.5-log
Cryptosporidium reduction in presedimentation processes. EPA has
reviewed the additional data submitted by commenters on the removal of
turbidity and aerobic spores (as an indicator of Cryptosporidium
removal) in full-scale presedimentation basins. These data are
consistent with data reviewed for the proposal in showing that when
turbidity removal was below 0.5-log, removal of aerobic spores was also
usually below 0.5-log. Conversely, when turbidity reduction exceeded
0.5-log, aerobic spore removal was typically higher than 0.5-log.
Consequently, while there is not a one-to-one relationship between
reduction in turbidity and reduction in aerobic spores, 0.5-log
turbidity reduction is a reasonable indicator of when Cryptosporidium
removal is likely to be at least 0.5-log.
EPA recognizes, though, that 0.5-log turbidity reduction through
presedimentation will not be feasible for some PWSs when raw water
turbidity is low. Today's final rule contains several provisions to
address this concern. First, PWSs can receive credit for
presedimentation during any month the process achieves 0.5-log
turbidity removal. Thus, PWSs that cannot achieve 0.5-log turbidity
reduction year-round may receive credit for presedimentation in those
months when they can meet this condition. Today's rule also allows PWSs
to receive presedimentation credit using State-approved performance
criteria other than turbidity reduction. If approved by the State, a
PWS may receive credit for presedimentation by demonstrating, for
example, 0.5-log reduction in aerobic spores. Finally, if
presedimentation improves treatment plant performance by reducing and
equalizing particle loading, a PWS can receive additional treatment
credit under today's rule for achieving lower filtered water turbidity
(see section IV.D.7).
5. Two-Stage Lime Softening
a. Today's Rule
Lime softening in drinking water treatment involves the addition of
lime and other chemicals to remove hardness (calcium and magnesium)
through precipitation. In single-stage softening, chemical addition and
hardness precipitation occur in a single clarification process prior to
filtration. In two-stage softening, chemical addition and hardness
precipitation occur in each of two sequential clarification processes
prior to filtration. In some water treatment plants, a portion of the
raw water bypasses a softening process (i.e., split softening) in order
to achieve a desired pH and alkalinity level in the treated water.
Under today's rule, single-stage softening with filtration receives
a prescribed 3.0-log credit towards Cryptosporidium treatment
requirements, which is equivalent to conventional treatment (see
section IV.B). Two-stage softening receives an additional 0.5-log
Cryptosporidium treatment credit during any month a PWS meets the
following conditions:

(1) Chemical addition and hardness precipitation occur in two
separate and sequential softening stages prior to filtration; and
(2) Both softening stages treat the entire plant flow taken from
surface water sources or GWUDI (i.e., no portion of the plant flow
from a surface water source may bypass either softening stage).

Alternatively, PWSs may apply to the State for Cryptosporidium
treatment credit for softening processes using a demonstration of
performance, as described in section IV.D.9. Demonstration of
performance provides an option for PWSs with softening processes that
do not meet these conditions for prescribed treatment credit and for
PWSs who seek greater than the prescribed Cryptosporidium treatment
credit for their softening processes.
b. Background and Analysis
Lime softening is a common practice that PWSs use to reduce water
hardness, which is primarily calcium and magnesium. The addition of
lime elevates the pH of the raw water. Elevation to pH 9.4 or higher
causes precipitation of calcium carbonate and further elevation to pH
10.6 or higher causes precipitation of magnesium hydroxide. Soda ash
may be added with lime to precipitate non-carbonate hardness. Removal
of the precipitate occurs through clarification (e.g., sedimentation
basin) and filtration processes. Coagulants and recycled softening
sludge are often used to enhance removal. In two-stage softening, the
second stage is commonly used to precipitate magnesium, along with
increased levels of calcium.
In addition to reducing hardness, softening processes remove
particulate material present in the raw water, including microbial
pathogens like Cryptosporidium. Particulate material flocculates with
the softening precipitate and is removed through the clarification and
filtration processes, similar to a conventional treatment plant. The
degree of Cryptosporidium removal will depend on the amount of
precipitate formation, the use of coagulants, the raw water quality,
and other factors. Available data indicate that the elevated pH used in
softening does not inactivate Cryptosporidium or Giardia (Logsdon et
al. 1994, Li et al. 2001), though it does inactivate some microorganisms
like viruses (Battigelli and Sobsey, 1993, Logsdon et al. 1994).
The Stage 2 M-DBP Advisory Committee recommended that lime
softening be eligible for up to 1.0-log additional Cryptosporidium
treatment credit based on a site-specific demonstration of performance,
but did not recommend any prescribed credit for this process (USEPA
2000a). After reviewing available data, however, EPA included a
prescribed 0.5-log Cryptosporidium treatment credit for two-stage lime
softening in the August 11, 2003 proposal (USEPA 2003a). This approach
reflected a recommendation by the SAB, which supported an additional
0.5-log treatment credit for two-stage lime softening if all the water
passes through both stages (SAB 2003). The proposal also allowed for
greater treatment credit through a demonstration of performance. The
following discussion summarizes the basis for the lime softening
treatment credit in today's final rule and differences with the proposal.
In the proposal, EPA reviewed a study by Logsdon et al. (1994) that
evaluated

[[Page 692]]

Cryptosporidium removal in full-scale lime softening plants.
Cryptosporidium was detected in the raw water at 5 plants: one single-
stage plant and four two-stage plants. Based on measured levels, the
removal of Cryptosporidium across the softening clarification
(sedimentation) stages was 1.0-log in the single stage plant and ranged
from 1.1-to 2.3-log in the two-stage plants. Cryptosporidium reductions
from raw to filtered water were 0.6- and 2.2-log in the single stage
plant and ranged from greater than 2.67- to greater than 3.85-log in
the two-stage plants.
EPA also evaluated data collected by PWSs on the removal of aerobic
spores in full-scale lime softening plants. As discussed earlier,
studies have shown the removal of aerobic spores to be an indicator for
Cryptosporidium removal, and one pilot-scale study of a softening plant
found significantly greater removal of Cryptosporidium than aerobic
spores under similar treatment conditions (Clark et al., 2001). For the
full-scale plants, average reductions in aerobic spores across the
softening clarification stages were 2.4- and 2.8-log for two plants
that practice two-stage softening and were 1.6- and 2.4-log for two
plants that practice single-stage softening (USEPA 2003a).
The Cryptosporidium removal data from Logsdon et al. (1994) and the
aerobic spore removal data provided by PWSs indicate that a lime
softening clarification stage can achieve greater than 0.5-log
Cryptosporidium removal during routine operation. Consequently, EPA
agrees with the SAB recommendation to award an additional 0.5-log
Cryptosporidium treatment credit for two-stage softening. Today's rule
establishes two-conditions for PWSs to receive this credit.
The first condition for 0.5-log treatment credit for two-stage
softening is that chemical addition and hardness precipitation must
occur in two separate and sequential softening stages prior to
filtration. The purpose of this condition is to ensure that plants
receiving additional credit for two-stage softening actually have
softening and associated particle removal occurring in each of two
sequential clarification stages. Plants with other types of
clarification processes in series with a softening stage are not
eligible for two-stage softening credit. Such plants may, however, be
eligible for additional treatment credit for other microbial toolbox
options, such as presedimentation, or may achieve additional credit
through a demonstration of performance.
The second condition for two-stage softening treatment credit is
that both softening stages must treat the entire plant flow taken from
a surface water source or GWUDI. The SAB recommended this condition,
which reflects the understanding that a softening stage is unlikely to
reduce overall Cryptosporidium levels by 0.5-log or more if it treats
only a fraction of the plant flow.
EPA recognizes that some PWSs using softening will bypass a
softening stage in order to maintain a desired pH and alkalinity level
in the treated water, and EPA is not recommending against this practice
generally. Rather, the restriction on bypassing a softening stage in
today's rule applies only to PWSs that seek additional treatment credit
for softening. Additionally, plants that soften both surface water and
ground water are eligible for softening treatment credit if they bypass
a softening stage only with ground water that is not under the direct
influence of surface water.
The proposal also required that a coagulant be present in both
clarifiers for a PWS to be eligible for additional treatment credit for
two-stage softening. EPA is not establishing this requirement in
today's final rule. While many PWSs that practice softening add
coagulants to improve the removal of precipitates and other particles,
the SAB did not recommend coagulant addition as a condition for
receiving treatment credit. Further, available data do not indicate
that additional coagulant is necessary to achieve at least 0.5-log
Cryptosporidium removal across a softening clarification stage if
hardness precipitation is occurring.
c. Summary of Major Comments
Public comments on the August 11, 2003, LT2ESWTR proposal supported
awarding additional Cryptosporidium treatment credit for lime softening
processes. EPA received specific comments on the types of lime
softening processes eligible for additional treatment credit, the
amount of additional treatment credit awarded, and the need for a
coagulant. A summary of these commenters' concerns and EPA's responses
follows.
In regard to the types of lime softening processes eligible for
treatment credit, commenters recommended that EPA better define two-
stage softening. Commenters stated that two-stage softening involves
two separate reaction chambers with the addition of the softening
chemical at the beginning of each chamber. Some commenters recommended
that eligibility for additional treatment credit should be based on the
level of softening precipitate formed or the settled water turbidity
and not on whether a plant practices single- or two-stage softening.
Another commenter recommended that any plant designs with multiple,
continuously operated clarification processes in series should be
eligible for additional treatment credit.
In response, EPA has refined the definition of two-stage softening
in today's final rule, which requires that softening processes employ
chemical addition and hardness precipitation in two sequential stages
to be eligible for the prescribed additional treatment credit. EPA
agrees with commenters that the level of precipitate formation will
influence the degree of Cryptosporidium removal. Available data,
however, indicate that two-stage softening will generally achieve more
Cryptosporidium removal than single-stage softening. Consequently, EPA
believes that two-stage softening should be eligible for the additional
prescribed 0.5-log treatment credit. Plants with single-stage softening
may receive additional treatment credit under today's rule through a
demonstration of performance. Similarly, plants that employ multiple
clarification process other than softening in series may receive
additional treatment credit either as presedimentation or through a
demonstration of performance.
With respect to the amount of additional Cryptosporidium treatment
credit for two-stage softening, most commenters supported awarding 3.0-
log treatment credit to single-stage lime softening, equivalent to a
conventional treatment plant, and an additional prescribed 0.5-log
treatment credit for two-stage lime softening. A few commenters
requested that two-stage lime be granted an additional Cryptosporidium
treatment credit of 1.0-log, based on the level of aerobic spore
removal measured across softening clarifiers.
EPA agrees with most commenters and the SAB that 0.5-log is an
appropriate level of additional prescribed Cryptosporidium treatment
credit for two-stage softening. Where plants are able to demonstrate a
significantly higher level of removal of Cryptosporidium or an
indicator like aerobic spores, they may apply for additional treatment
credit through a demonstration of performance.
Commenters stated that achieving particle removal in lime softening
is not dependent on a coagulant like a metal salt or organic polymer.
Some commenters recommended that coagulant be defined to include
softening chemicals like lime and magnesium hydroxide (a softening

[[Page 693]]

precipitate). EPA agrees that available data do not demonstrate the
need for a traditional metal salt or organic coagulant for effective
particle removal in softening. Accordingly, today's final rule does not
require the use of a coagulant as a condition for additional treatment
credit in two-stage softening. Instead, each stage must involve
chemical addition and hardness precipitation. EPA intends this
requirement to ensure that softening and associated particle removal
occur in each stage if a plant is to receive additional treatment
credit for two-stage softening.
6. Bank Filtration
a. Today's Rule
Bank filtration is a water treatment process that uses one or more
pumping wells to induce or enhance natural surface water infiltration
and to recover that surface water from the subsurface after passage
through a river bed or bank(s). Under today's rule, bank filtration
that serves as pretreatment to a filtration plant is eligible for
Cryptosporidium treatment credit if it meets the following criteria:
? Wells with a ground water flow path of at least 25 feet
receive 0.5-log treatment credit; wells with a ground water flow path
of at least 50 feet receive 1.0-log treatment credit. The ground water
flow path must be determined as specified in this section.
? Only wells in granular aquifers are eligible for treatment
credit. Granular aquifers are those comprised of sand, clay, silt, rock
fragments, pebbles or larger particles, and minor cement. A system must
characterize the aquifer at the well site to determine aquifer
properties. Systems must extract a core from the aquifer and
demonstrate that in at least 90 percent of the core length, grains less
than 1.0 mm in diameter constitute at least 10 percent of the core material.
? Only horizontal and vertical wells are eligible for treatment credit.
? For vertical wells, the ground water flow path is the
measured distance from the edge of the surface water body under high
flow conditions (determined by the 100 year floodplain elevation
boundary or by the floodway, as defined in Federal Emergency Management
Agency flood hazard maps) to the well screen. For horizontal wells, the
ground water flow path is the measured distance from the bed of the
river under normal flow conditions to the closest horizontal well
lateral screen.
? Systems must monitor each wellhead for turbidity at least
once every four hours while the bank filtration process is in
operation. If monthly average turbidity levels, based on daily maximum
values in the well, exceed 1 NTU, the system must report this result to
the State and conduct an assessment within 30 days to determine the
cause of the high turbidity levels in the well. If the State determines
that microbial removal has been compromised, the State may revoke
treatment credit until the system implements corrective actions
approved by the State to remediate the problem.
? Springs and infiltration galleries are not eligible for
treatment credit under this section, but are eligible for credit under
the demonstration of performance provisions described in section IV.D.9.
Alternatively, PWSs may apply to the State for Cryptosporidium
treatment credit for bank filtration using a demonstration of
performance. States may award greater than 1.0-log Cryptosporidium
treatment credit for bank filtration based on a site-specific
demonstration. For a bank filtration demonstration of performance
study, today's rule establishes the following criteria:
? The study must follow a State-approved protocol and must
involve the collection of data on the removal of Cryptosporidium or a
surrogate for Cryptosporidium and related hydrogeologic and water
quality parameters during the full range of operating conditions.
? The study must include sampling both from the production
well(s) and from monitoring wells that are screened and located along
the shortest flow path between the surface water source and the
production well(s).

The Toolbox Guidance Manual provides guidance on conducting site-
specific bank filtration studies, including analytical methods for
measuring aerobic and anaerobic spores, which may serve as surrogates
for Cryptosporidium removal.
PWSs using existing bank filtration as pretreatment to a filtration
plant at the time the PWS must begin source water Cryptosporidium
monitoring under today's rule must sample the well for the purpose of
determining bin classification. These PWSs are not eligible to receive
additional treatment credit for bank filtration. In these cases, the
performance of the bank filtration process in reducing Cryptosporidium
levels will be reflected in the monitoring results and bin classification.
PWSs using bank filtration without additional filtration must
collect source water samples in the surface water (i.e., prior to bank
filtration) to determine bin classification unless the State approves
an alternative monitoring location. This applies to systems using bank
filtration to meet the Cryptosporidium removal requirements of the
IESWTR or LT1ESWTR under the provisions for alternative filtration
demonstration in 40 CFR 141.173(b) or 141.552(a). Bank filtration
criteria for Cryptosporidium removal credit under today's rule do not
apply to existing State actions regarding alternative filtration
Cryptosporidium removal credit for IESWTR or LT1ESWTR compliance. PWSs
using GWUDI sources must collect samples from the well (i.e., the
ground water).
b. Background and Analysis
Bank filtration is a water treatment process that makes use of
surface water that has naturally infiltrated into ground water through
a river bed or bank and is recovered via a pumping well. River bed
infiltration is typically enhanced by the pumping action of nearby
wells. Bank filtrate is water that is drawn into a pumping well from a
nearby surface water source after having traveled through the
subsurface (i.e., aquifer) and mixing with other ground water. In bank
filtration, microorganisms and other particles are removed by contact
with the aquifer materials.
The Stage 2 M-DBP Advisory Committee recommended a prescribed
Cryptosporidium treatment credit of 1.0-log for bank filtration with
the option for PWSs to receive greater treatment credit through a site-
specific demonstration of performance (USEPA 2000a). The August 11,
2003 proposal included criteria, similar to those in today's final
rule, for PWSs to receive prescribed treatment credits of 0.5- and 1.0-
log (USEPA 2000a). The following discussion summarizes the basis for
these credits and for differences in associated requirements between
the proposal and today's final rule.
Directly measuring the removal of Cryptosporidium through bank
filtration is difficult due to the relatively low oocyst concentrations
typically present in surface and ground water. In the proposal, EPA
reviewed bank filtration field studies that measured the removal of
Cryptosporidium surrogates, specifically aerobic and anaerobic
bacterial endospores (Havelaar et al. 1995, Rice et al. 1996, Pang et
al. 1998, Arora et al. 2000, Medema et al. 2000, and Wang et al. 2001).
These microorganisms are suitable surrogates because they are resistant
to inactivation in the subsurface, similar in size and shape to
Cryptosporidium, and present in both surface and ground water at
concentrations that allow calculation of log removal across the surface
water-

[[Page 694]]

ground water interface and within the aquifer. In addition, EPA
reviewed studies of the transport of Cryptosporidium through soil
materials in laboratory column studies (Harter et al. 2000).
Based on these studies, EPA concluded that bank filtration
processes can achieve significant Cryptosporidium removal and that
prescribed Cryptosporidium treatment credits of 0.5-log and 1.0-log are
appropriate under certain conditions. These conditions are as follows:
Only wells located in unconsolidated, predominantly sandy aquifers are
eligible
The bank filtration removal process performs most efficiently when
the aquifer is comprised of granular materials with open pore-space for
water flow around the grains. In these granular porous aquifers, the
flow path is meandering, thereby providing ample opportunity for
microorganisms to come into contact with and attach to a grain surface.
Accordingly, only wells located in unconsolidated, granular aquifers
are eligible for bank filtration treatment credit.
Granular aquifers are those comprised of sand, clay, silt, rock
fragments, pebbles or larger particles and minor cement. Specifically,
a PWS must extract a core from the aquifer and demonstrate that in at
least 90 percent of the core length, grains less than 1.0 mm in
diameter constitute at least 10 percent of the core material.
Laboratory column studies of Cryptosporidium transport (Harter et al.,
2000) and field studies of aerobic bacterial endospore passage in the
subsurface (Pang et al., 1998) support these criteria.

Only Horizontal and Vertical Wells Are Eligible

A number of devices are used for the collection of ground water
including horizontal and vertical wells, spring boxes, and infiltration
galleries. Among these, only horizontal and vertical wells are eligible
for log removal credit because spring boxes and infiltration galleries
are components of engineered systems designed to speed transport
through or by-pass the naturally protective riverbed or bank.

Wells Must be Located 25 Feet From the Surface Water Source To Be
Eligible for 0.5-Log Credit and Located at Least 50 Feet From the
Surface Water Source To Be Eligible for 1.0-Log Credit

A vertical or horizontal well located adjacent to a surface water
body is eligible for bank filtration credit if there is sufficient
ground water flow path length to effectively remove oocysts.
Specifically, the ground water flow path must be at least 25 feet and
50 feet for 0.5-log and 1.0-log Cryptosporidium treatment credit,
respectively. The ground water flow path to a vertical well is the
measured distance from the edge of the surface water body under high
flow conditions (determined by the 100 year floodplain elevation
boundary or floodway, as defined in Federal Emergency Management Agency
flood hazard maps) to the wellhead. The ground water flow path to a
horizontal well is the measured distance from the bed of the river
under normal flow conditions to the closest horizontal well lateral.
These required flow path distances for Cryptosporidium treatment
credit are based on pathogen and surrogate monitoring data from bank
filtration field studies (Wang et al. 2001, Havelaar et al. 1995,
Medema et al. 2000). Results from these studies show that significant
removal of anaerobic and aerobic spores can occur during passage across
the surface water--ground water interface, with lesser removal
occurring during ground water transport within the aquifer away from
that interface. The ground water--surface water interface is usually
comprised of finer grained material that lines the bottom of the
riverbed. Typically, the thickness of the interface is small, ranging
from a few inches to a foot.
These results suggest that during normal and low surface water
elevations, the surface water-ground water interface will perform
effectively to remove microbial contamination like Cryptosporidium.
During short periods of flooding, substantially lower removal rates may
occur due to scouring of the riverbed and removal of the protective,
fine-grained material. Assessing the mean Cryptosporidium removal that
a bank filtration process will achieve over the period of a year
requires consideration of both high and low removal periods. By
considering all time intervals with differing removal rates over the
period of a year, EPA concluded that 0.5-log removal over 25 feet and
1.0-log removal over 50 feet are appropriate estimates of the mean
performance of a bank filtration process (USEPA 2003a).

Wells Must Be Continuously Monitored for Turbidity

Similar pathogen removal mechanisms are expected to occur in slow
sand filtration and bank filtration. Under the 40 CFR 141.73(b)(1), the
turbidity level of slow sand filtered water must be 1 NTU or less in 95
percent of the measurements taken each month. Turbidity sampling is
required once every four hours, but may be reduced to once per day
under certain conditions. Just as turbidity monitoring is used to
provide assurance that the removal credit assigned to a slow sand
filter is being realized, today's rule requires turbidity monitoring at
least once every 4 hours for all bank filtration wells that receive
treatment credit.
If monthly average turbidity levels (based on daily maximum values
in the well) exceed 1 NTU, the PWS must report this result to the State
and conduct an assessment to determine the cause of the high turbidity
levels in the well. If the State determines that microbial removal has
been compromised, the State may revoke treatment credit until the PWS
implements corrective actions to remediate the problem.

Demonstration of Performance

EPA recognizes that some bank filtration processes may achieve mean
Cryptosporidium removal greater than 1-log. Consequently, today's rule
allows PWSs to receive greater than 1.0-log Cryptosporidium treatment
credit for bank filtration through a State-approved demonstration of
performance study. This allowance is a change from the proposed rule,
which did not explicitly recognize demonstration of performance for
bank filtration (USEPA 2003a). This change reflects EPA's agreement
with public comment, described next, which recommended that EPA
explicitly recognize the option to conduct a bank filtration
performance study for greater than 1.0-log treatment credit.
A demonstration of performance study must involve the collection of
data on the removal of Cryptosporidium or surrogates and related
hydrogeologic and water quality parameters during the full range of
operating conditions. PWSs must sample from both the production well(s)
and one or more monitoring wells that are screened and located along
the shortest flow path between the surface water and the production
well(s). This will allow determination of the removal efficiency of the
aquifer.
Because directly measuring Cryptosporidium removal will not be
feasible for most PWSs, today's rule allows PWSs to sample for a State-
approved indicator, such as aerobic bacterial endospores. Research has
shown that aerobic spores can be very mobile in the subsurface
environment (Pang et al. 1998), and data collected by Wang et al.
(2001) indicate that aerobic spores are present in some surface waters
in sufficient quantity to allow measurement of log removal values.
EPA has provided guidance on conducting site-specific bank filtration

[[Page 695]]

studies in the Toolbox Guidance Manual. This guidance discusses data
needs and analysis for a performance demonstration so that the State
may tailor the study plan to meet site-specific hydrogeological and
operational conditions.
In summary, EPA believes that full-scale field data support
prescribed Cryptosporidium treatment credit up to 1.0-log for bank
filtration under the required conditions for set-back distance, aquifer
material, collection device type, and turbidity monitoring.
Demonstration of performance provides an appropriate opportunity for
States to award higher Cryptosporidium treatment credit for bank
filtration on a site-specific basis.
For PWSs using bank filtration when they must conduct source water
monitoring for bin classification, the required sampling locations
reflect the intent for this monitoring to capture the level of
Cryptosporidium entering a PWS's primary filtration treatment process.
Where bank filtration serves as pretreatment to a filtration plant,
PWSs must collect source water samples after bank filtration but prior
to the filtration plant. In this case, the Cryptosporidium removal that
bank filtration achieves will be reflected in the monitoring results
and bin classification for the filtration plant. In contrast, where
bank filtration is the primary filtration process, meaning that a PWS
uses bank filtration to comply with the Cryptosporidium treatment
requirements of the IESWTR or LT1ESWTR, PWSs must collect samples in
the surface water source (e.g, the river).
c. Summary of Major Comments
Public comments on the August 11, 2003, LT2ESWTR proposal supported
awarding Cryptosporidium treatment credit for bank filtration. Many
commenters, however, stated that the proposed levels of credit (0.5-
and 1.0-log) were insufficient. To address this issue, commenters
supported allowing PWSs to obtain greater treatment credit by
performing a site-specific study of bank filtration removal efficiency.
Commenters recommended that site-specific bank filtration studies
involve the measurement of surrogates for Cryptosporidium removal using
monitoring wells located along the shortest flow path between the
surface water and the production well.
EPA agrees that some bank filtration sites may achieve greater than
1.0-log Cryptosporidium removal. Today's rule establishes the proposed
bank filtration Cryptosporidium treatment credits of 0.5- and 1.0-log
and allows PWSs to apply to the State for higher levels of credit
through a site-specific demonstration of performance. In such a study,
PWSs must measure the removal of Cryptosporidium or a State-approved
surrogate using monitoring wells located along the flow path, as
recommended by commenters.
Some commenters cited research addressing appropriate surrogate
organisms for estimating Cryptosporidium removal in surface water
treatment plants and bank filtration sites. Commenters recommended that
EPA recognize aerobic endospores as a surrogate measure in
Cryptosporidium removal studies, including those for bank filtration.
EPA agrees that based on available information, aerobic spores are
suitable Cryptosporidium removal surrogates for bank filtration
processes due to their size, resistance to inactivation, and
concentration in surface and ground waters. Data from several bank
filtration sites on the use of aerobic spores as a Cryptosporidium
removal surrogate are available. The Toolbox Guidance Manual identifies
aerobic spores as suitable in conjunction with other hydrogeologic data
for making site-specific determinations for additional Cryptosporidium
removal credit.
In guidance, EPA suggests that where feasible, PWSs measure diatom
species in conjunction with aerobic spores in bank filtration studies
because Cryptosporidium oocysts are intermediate in size between the
two surrogate groups. Further, EPA recognizes the current uncertainties
and limitations in available information on surrogates for bank
filtration and will update guidance as warranted by new information.
7. Combined Filter Performance
a. Today's Rule
For water treatment plants that use filtration, the turbidity of
the filtered water is an indicator of how effectively the plant is
removing particulate matter, including microbial pathogens, from the
raw water. PWSs using conventional filtration treatment or direct
filtration receive an additional 0.5-log Cryptosporidium treatment
credit during any month the PWS meets the following standard:
? The turbidity level of representative samples of a PWS's
filtered water (i.e., the combined filter effluent) is less than or
equal to 0.15 NTU in at least 95 percent of the measurements taken each
month. PWSs must continue to measure turbidity as specified in 40 CFR
141.74(a) and (c), which generally require sampling at least every four
hours using approved methods.

PWSs using other types of filtration processes, including slow sand,
diatomaceous earth, membranes, bag, or cartridge filtration, are not
eligible for this treatment credit.
b. Background and Analysis
Turbidity is a method defined parameter that is based on measuring
the amount of light scattered by suspended particles in a solution.
This measure can detect the presence of a wide variety of particles in
water, including microorganisms, but cannot provide specific
information on particle type, number, or size. In filtered water, the
turbidity level indicates how well the filtration and other upstream
clarification processes have performed in removing particles from the
raw water, with lower turbidity indicating better particle removal.
Thus, lower filtered water turbidity is associated with a decreased
likelihood that microbial pathogens like Cryptosporidium have passed
through the filtration plant and into the water distributed to consumers.
Under existing regulations, PWSs that filter must monitor turbidity
in the combined filter effluent (CFE) at least every four hours using
approved methods, although States may reduce this frequency to once per
day for PWSs serving 500 people or fewer (40 CFR 141.74(a) and (c)).
For PWSs using conventional or direct filtration, at least 95 percent
of the CFE turbidity measurements must be less than or equal to 0.3
NTU, and the turbidity must never exceed 1 NTU (40 CFR 141.173(a) and
141.551(a)-(b)).
The Stage 2 M-DBP Advisory Committee recommended an additional 0.5-
log Cryptosporidium treatment credit for PWSs that achieve a CFE
turbidity less than or equal to 0.15 NTU in at least 95 percent of
measurements per month (USEPA 2000a). This 95th percentile turbidity
standard is one half the level required under existing regulations for
PWSs using conventional or direct filtration, as stated earlier. The
August 11, 2003 proposal included this treatment credit for PWSs using
conventional or direct filtration (USEPA 2003a), and EPA is
establishing it in today's final rule with no changes from the
proposal. The following discussion summarizes the basis for this
treatment credit.
In the proposal, EPA analyzed the improvement in Cryptosporidium
removal that conventional and direct filtration plants realize when
operating at lower effluent turbidity levels. For this analysis, EPA
estimated that PWSs

[[Page 696]]

complying with the existing 95th percentile CFE turbidity standard of
0.3 NTU will typically operate with filter effluent turbidity between
0.1-0.2 NTU; PWSs complying with a CFE standard of 0.15 NTU were
estimated to operate with filter effluent turbidity less than 0.1 NTU.
Accordingly, EPA compared Cryptosporidium removal efficiencies when
effluent turbidity was below 0.1 NTU with those when effluent turbidity
was in the range of 0.1-0.2 NTU.
Studies by Patania et al. (1995), Emelko et al. (1999), and Dugan
et al. (2001) observed the average removal of Cryptosporidium to be
0.5-to 1.2-log greater when filter effluent turbidity was less than 0.1
NTU in comparison to removal with effluent turbidity between 0.1-0.2
NTU. These studies, therefore, indicate that PWSs complying with a
filter effluent turbidity standard of 0.15 NTU will achieve at least
0.5-log greater Cryptosporidium removal than PWSs complying with the
existing 0.3 NTU standard. Based on this finding, EPA concluded that an
additional 0.5-log Cryptosporidium treatment credit is appropriate for
PWSs using conventional or direct filtration that meet a 95th
percentile CFE turbidity standard of 0.15 NTU.
Other types of filtration processes, such as slow sand,
diatomaceous earth, membranes, bag, or cartridge filtration, are not
eligible for this treatment credit. These filtration processes remove
Cryptosporidium through different mechanisms than those operative in
rapid granular media filtration, which is used in conventional and
direct filtration. Available data do not establish a similar
relationship between lower filter effluent turbidity and improved
Cryptosporidium removal efficiency for these other filtration processes.
The SAB reviewed the proposed additional Cryptosporidium treatment
credit for PWSs that operate with very low filtered water turbidity. In
their report, the SAB stated that further lowering of turbidity would
result in further reductions in Cryptosporidium in the effluent from
filtration processes, but available data were limited in showing the
exact removal that can be achieved. Based on the data provided, the SAB
recommended that no additional treatment credit be given to plants that
demonstrate a CFE turbidity of 0.15 NTU or less (SAB 2003).
In addressing this SAB recommendation, EPA recognizes that
precisely quantifying the increase in Cryptosporidium removal that a
particular filtration plant will realize when operating at lower filter
effluent turbidity is not generally feasible. Available data, though,
consistently show that removal of Cryptosporidium is at least 0.5-log
greater when filter effluent turbidity reflects compliance with a 0.15
NTU standard in comparison to a 0.3 NTU standard. Further, treatment
plants operating at lower filter effluent turbidity will achieve
increased removal of other microbial pathogens present in the raw
water. In consideration of these factors, EPA believes that PWSs should
receive an additional 0.5-log Cryptosporidium treatment credit when at
least 95 percent of CFE turbidity measurements are less than or equal
to 0.15 NTU.
Another key issue in establishing additional treatment credit based
on low filtered water turbidity is the performance of analytical
instruments (turbidimeters) to accurately measure turbidity at low
levels. In the proposal, EPA reviewed studies of low level turbidity
measurements by EPA (1998c), Sadar (1999), and Letterman et al. (2001).
Among the significant findings of these studies are the following:

(1) On-line turbidimeters typically had a positive bias (i.e., a
higher turbidity reading) in comparison to bench-top turbidimeters.
EPA expects that most PWSs that receive additional treatment credit
for low filter effluent turbidity will use on-line turbidimeters.
This finding suggests that the error in turbidimeter readings may be
generally conservative, so that PWSs will operate at lower than
required turbidity levels.
(2) Different turbidimeters did not agree well when used to
measure low level turbidity, which may be due to differences in
instrument design. This finding suggests that low level turbidity
measurements may be viewed as a relative indicator of water quality
improvement at a particular PWS but may be less applicable for
making comparisons among different PWSs.

In addition, the American Society for Testing and Materials (ASTM)
has issued standard test methods for measurement of turbidity below 5
NTU by on-line (ASTM 2001) and static (ASTM 2003) instruments. These
methods specify that the instrument should permit detection of
turbidity differences of 0.01 NTU or less in waters having turbidities
of less than 1.00 NTU (ASTM 2001) and 5.0 NTU (ASTM 2003), respectively.
After reviewing these studies and the ASTM methods, EPA concluded
that currently available monitoring equipment can reliably measure
turbidity at levels of 0.15 NTU and lower. Rigorous calibration and
maintenance of turbidity monitoring equipment is necessary, however.
EPA has developed guidance on proper calibration, operation, and
maintenance of turbidimeters (USEPA 1999c).
c. Summary of Major Comments
Public comment on the August 11, 2003, LT2ESWTR proposal supported
awarding additional Cryptosporidium treatment credit for PWSs that
achieve lower filtered water turbidity. Commenters raised specific
concerns with the criteria for PWSs to receive this credit, the
available data that support this credit, and the performance of
turbidimeters for measuring turbidity at very low levels. A summary of
these comments and EPA's responses follows.
Most commenters supported awarding 0.5-log additional
Cryptosporidium treatment credit for PWSs that achieve at least 95
percent of CFE turbidity measurements less than or equal to 0.15 NTU. A
few commenters, however, recommended that PWSs only receive additional
treatment credit for demonstrating this level of turbidity performance
in each individual filter effluent (IFE), rather than the CFE. In
addition, one commenter stated that PWSs should be required to monitor
CFE turbidity every 15 minutes, rather than every four hours as
required under current regulations.
In response, EPA agrees with the recommendation of most commenters
and has established additional Cryptosporidium treatment credit based
on meeting a 95th percentile turbidity level of 0.15 NTU in the CFE.
EPA recognizes, however, that achieving low turbidity in each IFE may
represent a higher level of performance than achieving low turbidity in
the CFE. As described in the next section, EPA has also established
standards for additional Cryptosporidium treatment credit based on low
IFE turbidity in today's rule. EPA does not have data indicating that
PWSs should monitor the CFE turbidity at a higher frequency than every
four hours, as required under existing regulations. Consequently, EPA
is not changing the frequency of required CFE turbidity monitoring as a
condition for PWSs to receive additional treatment credit under today's
rule.
One commenter summarized additional studies that provide data on
the improvement in Cryptosporidium removal efficiency at lower filter
effluent turbidity levels. According to this commenter, these studies
demonstrate that lowering filter effluent turbidity from 0.3 to 0.15
NTU translates to an improvement in Cryptosporidium removal of more
than 1.5-log, with individual studies showing a range of >0.7-log to
>3-log based on median removal. EPA finds that these studies bolster
the conclusion that PWSs operating to meet 0.15 NTU in the filter
effluent will achieve at least 0.5-

[[Page 697]]

log greater Cryptosporidium removal than PWSs operating to meet 0.3
NTU. Thus, they support the additional 0.5-log Cryptosporidium
treatment credit under today's rule for PWSs meeting 0.15 NTU at the
95th percentile in the CFE.
In regard to the measurement of low level turbidity, some
commenters raised concerns that turbidimeters used by the U.S. water
supply industry do not agree when used to measure turbidity in the 0.01
to 0.5 NTU range. Further, these differences are independent of the
calibration method used and can be significant when comparing
instruments by different manufacturers. Other commenters stated that
turbidimeters can accurately reflect turbidity values less than 0.15
NTU if properly calibrated, and some commenters cited the ASTM method
development process to support this assessment. In addition, commenters
suggested that available guidance on turbidity measurement provides
quality assurance measure that can reduce analytical uncertainty.
EPA agrees with commenters that available methods and instruments
are adequate to demonstrate compliance with a 0.15 NTU turbidity level.
In particular, EPA believes that monitoring low level turbidity can be
effective for demonstrating water quality improvements at individual
plants, but also recognizes that the performance of turbidimeters used
at different plants may vary. Further, calibration and maintenance of
turbidity monitoring equipment is critical, and EPA has developed
guidance on these procedures (USEPA 1999c).
8. Individual Filter Performance
a. Today's Rule
PWSs using conventional filtration treatment or direct filtration
receive an additional 0.5-log Cryptosporidium treatment credit during
any month the PWS meets the following criteria:
? The filtered water turbidity for each individual filter is
less than or equal to 0.15 NTU in at least 95 percent of the
measurements recorded each month; and
? No individual filter has a measured turbidity level greater than 0.3
NTU in two consecutive measurements taken 15 minutes apart.
PWSs must continue to monitor turbidity for each individual filter
continuously and record the results every 15 minutes, as required under
40 CFR 141.174 and 141.560.
PWSs that receive this 0.5-log Cryptosporidium treatment credit for
individual filter performance also receive 0.5-log treatment credit for
combined filter performance, as described in section IV.D.7, for a
total additional treatment credit of 1.0-log. Conversely, PWSs are not
required to pursue individual filter performance credit to remain
eligible for combined filter performance credit.
If a PWS has received credit for individual filter performance to
comply with its Cryptosporidium treatment requirements and fails to
meet the required criteria for this credit during any month, the PWS
will not incur a treatment technique violation if the State determines
the following:
? The failure to meet the required criteria for individual
filter performance treatment credit was due to unusual and short-term
circumstances that could not reasonably be prevented through optimizing
treatment plant design, operation, and maintenance; and
? The PWS has experienced no more than two such failures in
any calendar year.
This treatment credit is not applicable to other types of
filtration processes, including slow sand, diatomaceous earth,
membranes, bag, or cartridge filtration.
b. Background and Analysis
Awarding additional treatment credit for individual filter
performance is based on the expectation that achieving low filtered
water turbidity in each individual filter will provide increased
protection against microbial pathogens. Most treatment plants have
multiple filters. Moderately elevated turbidity in the effluent from a
single filter may not significantly affect the turbidity of the
combined filter effluent, but may indicate a reduction in the overall
pathogen removal efficiency of the filtration process. Consequently, a
primary goal in optimizing water treatment plant performance is
ensuring that each filter always produces very low turbidity water.
The criteria for PWSs to achieve the additional 1.0-log
Cryptosporidium treatment credit for individual filter performance
reflect goals of Phase IV of the Partnership for Safe Water
(Partnership). The Partnership is a voluntary cooperative program
involving PWSs, professional associations, and Federal and State
regulatory agencies that seeks to increase protection against microbial
contaminants by optimizing water treatment plant performance. The Stage
2 M-DBP Advisory Committee recommended 1.0-log treatment credit for
PWSs that successfully participate in a peer review program and
identified Phase IV of the Partnership as a program where such credit
would be appropriate (USEPA 2000a).
At the time of the Advisory Committee recommendation, the
performance goals for Phase IV of the Partnership reflected those of
the EPA Composite Correction Program (USEPA 1991a) and involved an on-
site evaluation by a third-party team. Phase IV performance goals for
individual filters included filtered water turbidity less than 0.1 NTU
at least 95 percent of the time based on daily maximum values and a
maximum measurement of 0.3 NTU. The purpose of the on-site evaluation
was to confirm that a PWS had met Phase IV performance goals or had
achieved the highest level of performance given its unique raw water
quality.
After the Stage 2 M-DBP Agreement in Principle was signed in
September 2000, the Partnership eliminated on-site third-party
evaluation as a component of Phase IV. Instead, Phase IV required
completion of an Optimization Assessment Spreadsheet in which the PWS
entered water treatment data to demonstrate that it had achieved Phase
IV performance levels. The application also required narratives related
to the administrative support and operational capabilities necessary to
sustain performance long-term.
The August 11, 2003 LT2ESWTR proposal included a 1.0-log
Cryptosporidium treatment credit for PWSs that met the individual
filter performance goals of Phase IV of the Partnership (i.e., 95
percent of daily maximum values below 0.1 and no values above 0.3 NTU)
(USEPA 2003a). Rather than requiring an application package with
historical data and narratives, however, the proposed rule required
PWSs to report filter effluent turbidity data to the State each month
to demonstrate compliance with these filter performance goals.
The Partnership modified the Phase IV goals for individual filter
performance in 2003. A revised goal is filtered water turbidity less
than 0.10 NTU at least 95 percent of the time based on values recorded
at 15 minute time intervals. Thus, where the earlier goal was based on
daily maximum values for each filter, the revised goal is based on all
values for each filter--a less stringent approach. The Partnership made
this modification after finding that none of the water treatment plants
that had been evaluated could consistently meet the 0.1 NTU goal using
daily maximum values and, further, that this goal was biased against
plants with more filters.
In today's final rule, EPA has adjusted the criteria from the
proposal for PWSs

[[Page 698]]

to receive additional treatment credit based on individual filter
effluent turbidity. These adjustments are in response to the changes
the Partnership made to Phase IV individual filter performance goals.
Under today's rule, PWSs receive 1.0-log additional Cryptosporidium
treatment credit if effluent turbidity from each filter is less than or
equal to 0.15 NTU at least 95 percent of the time and never exceeds 0.3
NTU in two consecutive measurements taken 15 minutes apart.
EPA expects that PWSs will operate at less than 0.1 NTU in order to
comply with a regulatory limit of 0.15 NTU. Further, EPA believes that
assessing individual filter compliance with a maximum turbidity level
of 0.3 NTU based on two consecutive measurements taken 15 minutes apart
is appropriate. This approach allows for brief fluctuations in
turbidimeter readings that may not indicate a degradation in filtered
water quality to occur without penalizing a PWS, but it should catch
filters that significantly exceed 0.3 NTU over the course of a month.
EPA applied this approach to individual filter monitoring under the
IESWTR and LT1ESWTR. Consequently, EPA regards these criteria as
comparable to the revised Partnership Phase IV standards for individual
filter performance.
In addition, today's rule gives States authority to determine
whether to issue a treatment technique violation for PWSs that exceed
individual filter performance limits. This authority applies in the
case where a PWS receives credit for individual filter performance to
meet the treatment requirements of today's rule and fails to achieve
the criteria to receive this credit during a month. If the State
determines that this failure was due to unusual and short-term
circumstances that could not reasonably be prevented through treatment
optimization, the State may choose not to issue a treatment technique
violation, which the PWS otherwise will incur. Because this authority
should be applied only to unusual plant circumstances, a State cannot
make this determination if a PWS has experienced more than two such
failures in any calendar year.
EPA is granting States this authority because PWSs that
consistently meet the criteria for individual filter performance
treatment credit may occasionally experience short-term deviations from
these criteria due to circumstances largely beyond the PWS's control.
An example of such a circumstance may be malfunctioning equipment that
a PWS quickly removes from service, but that nevertheless prevents the
PWS from fully meeting individual filter performance criteria in a
particular month. EPA believes that States should only apply this
authority in cases where PWSs have consistently achieved the criteria
for individual filter performance treatment credit in previous months.
The approach in today's final rule for valuing individual filter
performance treatment credit differs from the approach in the proposal.
EPA's intent in both the proposal and today's rule is to award an
additional 1.0-log Cryptosporidium treatment credit to PWSs that meet
the criteria for individual filter performance. In the proposal,
however, PWSs could receive 1.0-log additional treatment credit
specifically for meeting the individual filter performance criteria,
but were then not eligible to receive any treatment credit under the
combined filter performance option. In today's rule, PWSs receive 0.5-
log credit for the individual filter performance option and also
receive an additional 0.5-log treatment credit for the combined filter
performance option (discussed in section IV.D.7), resulting in 1.0-log
total additional credit. EPA has made this modification so that if a
PWS fails in an attempt to achieve individual filter performance
credit, the PWS is clearly still eligible to received combined filter
performance credit.
In a review of a draft LT2ESWTR proposal, the SAB recommended that
PWSs receive 0.5-log, rather than 1.0-log, additional Cryptosporidium
treatment credit for achieving individual filter effluent turbidity
below 0.15 NTU at the 95th percentile (SAB 2003). In response to this
SAB recommendation, today's rule requires additional individual filter
performance criteria to support 1.0-log total additional treatment
credit. Specifically, today's rule incorporates the Partnership Phase
IV performance goal that individual filter effluent turbidity never
exceed 0.3 NTU (as described earlier, EPA concluded that determining
compliance with this standard based on two consecutive measurements
taken 15 minutes is appropriate and consistent with existing
regulations). Thus, EPA believes that these criteria, in conjunction
with the expectation that controlling effluent turbidity at all filters
individually rather than just the combined filter effluent will
generally result in lower microbial risk, justify 1.0-log additional
treatment credit.
c. Summary of Major Comments
Public comment on additional treatment credit for individual filter
performance in the August 11, 2003 proposal raised a number of issues:
changes in the Partnership Phase IV criteria and achievability of the
proposed criteria for this credit, credit for participating in peer
review programs, and a review process for data that exceed regulatory
limit. A summary of these comments and EPA's responses follows.
Several commenters stated that PWSs could not consistently achieve
the proposed individual filter effluent turbidity criterion of 95
percent of daily maximum measurements less than or equal to 0.1 NTU.
Commenters provided data on turbidity levels in PWSs to support this
assertion and indicated that the Partnership modified this criterion in
the Phase IV individual filter performance goals because PWSs could not
meet it. Alternatives recommended by commenters for the final rule
included the use of the revised Partnership Phase IV goals for
individual filter effluent turbidity or a more stringent criterion for
combined filter effluent turbidity.
In response, EPA agrees that current Partnership Phase IV goals
provide appropriate criteria for awarding 1.0-log total additional
Cryptosporidium treatment credit. Today's rule grants this total credit
to PWSs that meet a 95th percentile individual filter effluent
turbidity limit of 0.15 NTU, and EPA expects that PWSs complying with
this limit will operate under the Partnership goal of 0.10 NTU. EPA
does not support awarding a higher level of additional treatment credit
for a more stringent combined filter effluent turbidity criterion,
beyond the 0.5-log credit available under combined filter performance
(see section IV.D.7). The purpose of the individual filter performance
toolbox option is to recognize the higher pathogen removal PWSs will
likely achieve by maintaining very low effluent turbidity for each
individual filter.
A few commenters suggested that as an alternative to establishing
numerical criteria for individual filter performance, today's rule
should award additional treatment credit for PWSs that successfully
participate in a peer review program. In addition to the Partnership,
commenters listed the Area Wide Optimization Program and the Texas
Optimization Program as examples of programs that will provide for
comprehensive improvements in treatment performance.
EPA agrees that participation in peer review programs is beneficial
for PWSs. Further, such programs may assist PWSs in meeting the
filtration performance criteria in today's rule for additional
Cryptosporidium treatment credit. EPA does not believe, however, that
mere participation in a peer review program

[[Page 699]]

is an appropriate basis for awarding additional treatment credit.
Rather, to ensure national consistency in standards for compliance with
treatment requirements, EPA has concluded that additional treatment
credit should be based on PWSs meeting specified criteria for enhanced
treatment performance.
Another significant issue raised by commenters is the need for a
review process for deviations from the criteria for individual filter
performance due to circumstances that cannot be prevented through plant
optimization. An example given by several commenters is a filter that
malfunctions and is taken out of service, but that may have exceeded
the individual filter performance turbidity criteria for a short period
when the filter was operating.
EPA agrees that circumstances may occur that are beyond the PWS's
control and that prevent the PWS from fully meeting the criteria for
individual filter performance in a particular month. If a PWS relies on
individual filter performance treatment credit to meet the treatment
requirements of today's rule and the PWS fails to meet all criteria for
this credit in a given month, the State may review the reasons for this
failure. If the State finds that the failure was due to circumstances
that could not be prevented through plant optimization, the State may
choose not to issue a treatment technique violation on up to two such
occasions in a calendar year.
9. Demonstration of Performance
a. Today's Rule
A demonstration of performance is a site-specific test that
assesses the Cryptosporidium removal efficiency of a water treatment
plant or a treatment process within a plant. Under today's rule, PWSs
may undertake demonstration of performance testing for the following
purposes:

(1) To establish a Cryptosporidium treatment credit that is
higher than the prescribed treatment credit in today's rule for a
water treatment plant or a treatment process in the microbial toolbox; or
(2) To establish a Cryptosporidium treatment credit for a
treatment process that is not included in the microbial toolbox or
that does not meet the design or operational criteria for prescribed
treatment credit in the microbial toolbox.

The specific requirements that apply to demonstration of
performance testing are as follows:
? PWSs may receive Cryptosporidium treatment credit for a
water treatment plant or a treatment process within a plant that is
based on a site-specific demonstration of Cryptosporidium removal
efficiency. This demonstration of performance treatment credit may be
greater than or less than any prescribed treatment credit in today's rule.
? The site-specific demonstration of Cryptosporidium removal
efficiency must follow a State-approved protocol and may involve the
use of surrogates rather than Cryptosporidium.
? The State must approve through written notification any
treatment credit based on a demonstration of performance. As a
condition of approval, the State may designate monitoring and treatment
performance criteria the PWS must meet and report on an ongoing basis
to remain eligible for the credit. The State may designate such
criteria to verify that the PWS maintains the operating conditions
under which the State approved the demonstration of performance
treatment credit.
? PWSs are not eligible for prescribed treatment credit for
any treatment process that is included in a demonstration of
performance credit.
b. Background and Analysis
The prescribed Cryptosporidium treatment credits in today's rule
for water treatment plants and for treatment processes in the microbial
toolbox are based on conservative estimates of mean Cryptosporidium
removal efficiencies. Due to site-specific conditions, however, some
PWSs will achieve greater Cryptosporidium removal than reflected in the
prescribed treatment credits. In addition, some PWSs will have
treatment processes that are not included in the microbial toolbox or
that do not meet microbial toolbox criteria for prescribed treatment
credit. In all these cases, PWSs have the option to undertake
demonstration of performance testing to establish an appropriate level
of Cryptosporidium treatment credit for the treatment plant or
treatment process.
The option for demonstration of performance testing in today's rule
reflects a recommendation by the Stage 2 M-DBP Advisory Committee.
Specifically, the Committee stated that the LT2ESWTR should allow site-
specific testing both to establish Cryptosporidium treatment credit
above the prescribed credit for microbial toolbox processes and to
demonstrate Cryptosporidium removal for technologies not listed in the
microbial toolbox. The August 11, 2003 LT2ESWTR proposal included the
demonstration of performance option (USEPA 2003a), and EPA is
establishing it in today's final rule.
Demonstration of performance testing will be specific to a
particular site and will depend on the treatment processes being
tested, water quality, plant infrastructure, PWS resources, and other
factors. Consequently, today's rule does not establish specific
protocols for demonstration of performance testing. Rather, today's
rule gives States the authority to approve testing protocols developed
by PWSs and to determine what level of Cryptosporidium treatment credit
is appropriate. The Toolbox Guidance Manual provides recommendations to
PWSs and States on conducting demonstration of performance testing,
including analytical methods for measuring aerobic and anaerobic spores.
In general, demonstration of performance testing should encompass
the full range of expected operating conditions and should
conservatively assess the degree of Cryptosporidium removal that a
treatment process can reliably achieve. Directly quantifying the
removal of Cryptosporidium typically is not feasible in full-scale
testing due to limitations in source water concentrations and
analytical method performance. Consequently, demonstration of
performance testing that is conducted at full-scale may involve the use
of surrogates, such as aerobic spores, that have been shown to
correlate with the removal of Cryptosporidium. PWSs and States may also
consider the use of pilot-scale studies in conjunction with full-scale
studies for demonstration of performance testing.
As a condition of approving a demonstration of performance credit,
the State may designate treatment performance criteria the PWS must
meet on an ongoing basis to remain eligible for the credit. For
example, if a PWS conducts a demonstration of performance study while
operating with very low filtered water turbidity, the State may
establish as a condition of approving treatment credit based on the
study that the PWS must continue operating at the low filtered water
turbidity. EPA believes this condition is necessary because, in this
example, if the PWS were to begin operating at a higher filtered water
turbidity level, the demonstration of performance study results might
no longer represent the PWSs actual performance.
PWSs are not eligible for prescribed treatment credit for any
treatment process that is included in a demonstration of performance
credit. For example, if a PWS receives a demonstration of performance
treatment credit of 4-log for Cryptosporidium removal through a
conventional treatment plant (i.e., coagulation/sedimentation/
filtration), the PWS is not

[[Page 700]]

also eligible for additional treatment credit for combined filter
performance. In this case, the demonstration of performance testing
accounts for the removal achieved by filtration.
c. Summary of Major Comments
Public comment on the August 11, 2003 LT2ESWTR proposed supported
inclusion of the demonstration of performance option to award site-
specific treatment credit to PWSs. Commenters stated that many well-run
surface water treatment plants achieve significantly greater
Cryptosporidium removal than the prescribed treatment credit, and
demonstration of performance testing is needed to award an appropriate
level of credit in such cases. Two aspects of this option that received
significant public comment are the provision for States to award less
than the prescribed treatment credit if indicated by testing results
and the need for guidance on demonstration of performance testing.
These comments and EPA's responses are summarized as follows.
Several commenters recommended that EPA eliminate the provision
that allows States to award less than the prescribed treatment credit
based on demonstration of performance testing. These commenters stated
that pilot- and full-scale testing is conservative and challenging to
implement and that for past regulations, States generally have not
awarded lower treatment credit based on a site-specific study. If this
provision remains in the regulation, commenters suggested that EPA
provide criteria addressing how it should be applied. Such criteria
should recognize the conservative nature of testing with surrogates for
Cryptosporidium removal and the potential for misleading or flawed
testing results.
In response, EPA believes that States should have the discretion to
award either more or less treatment credit than the prescribed credit
on a case-by-case basis where a State has site-specific information
that an alternative credit is appropriate. Today's rule allows this.
EPA recognizes, however, that demonstration of performance testing
should be designed to provide a conservative estimate of treatment
efficiency and, as such, is not generally intended to reduce the level
of treatment credit a PWS receives. Further, results from demonstration
of performance testing should be rigorously evaluated for flaws and
bias prior to being used to support either a higher or lower treatment
credit. The Toolbox Guidance Manual identifies approaches States may
wish to consider in awarding higher or lower treatment credit.
Many commenters stated that EPA should provide thorough guidance on
demonstration of performance testing. Topics for this guidance
suggested by commenters include approaches to demonstrating treatment
credit, minimum duration of testing, the use of safety factors, and
periodic reconfirmation of testing results. Some commenters recommended
that guidance address both full-scale testing with surrogates like
aerobic spores and pilot-scale testing with Cryptosporidium or
surrogates. Other commenters recommended that testing should be limited
to full-scale processes and that testing with pilot-scale
representations of full-scale equipment should be discouraged.
In the Toolbox Guidance Manual, EPA provides direction on
procedures for demonstration of performance testing that addresses
issues raised by commenters. These issues include surrogates for full-
scale testing, potential roles for pilot-scale testing in conjunction
with full-scale testing, minimum duration of testing to capture the
full range of operating conditions, the analysis of data from testing
to establish treatment credit, and routine monitoring to verify that
the conditions under which demonstration of performance credit is
awarded are maintained during routine operation. EPA believes that this
guidance will assist PWSs and States with implementing demonstration of
performance testing appropriately.
10. Bag and Cartridge Filtration
a. Today's Rule
Under today's rule, PWSs may receive Cryptosporidium treatment
credit of up to 2.0-log for an individual bag or cartridge filter and
up to 2.5-log for two or more bag or cartridge filters operated in
series. To be eligible for this treatment credit, filters must meet the
definition of a bag or cartridge filter and must undergo challenge
testing to demonstrate removal efficiency with an applied safety
factor, as described in this section.
Today's rule defines bag and cartridge filters as pressure driven
separation processes that remove particulate matter larger than 1
micrometer using an engineered porous filtration media through either
surface or depth filtration. Bag filters are constructed of a non-
rigid, fabric filtration media housed in a pressure vessel in which the
direction of flow is from the inside of the bag to the outside.
Cartridge filters are typically constructed as rigid or semi-rigid,
self-supporting filter elements housed in a pressure vessel in which
flow is from the outside of the cartridge to the inside.
Today's rule treats bag and cartridge filters equivalently, with
the following exception: If a cartridge filter meets the definition of
a membrane filtration process and can be direct integrity tested
according to the criteria specified in section IV.D.11, a PWS has the
option to seek greater treatment credit for the filter as a membrane.
Section IV.D.11 describes criteria for awarding treatment credit to
membranes.
Today's rule requires challenge testing to establish
Cryptosporidium treatment credit for bag and cartridge filters. This
challenge testing is product-specific and not site-specific. Once
challenge testing is performed on a specific bag or cartridge
filtration product, PWSs that install the specific filtration product
are not required to repeat challenge testing at individual sites. For a
PWS to receive Cryptosporidium treatment credit for a bag or cartridge
filter, challenge testing must meet the following criteria:
? Challenge testing must be conducted on full-scale filters
that match the filters the PWS will use in materials, construction, and
associated housing or pressure vessel. If treatment credit will be
based on filters operated in series then challenge testing must be
performed on the filters in series.
? Challenge testing must involve measuring the removal by
the filter of either Cryptosporidium or a surrogate that is removed no
more efficiently than Cryptosporidium (i.e., the ``challenge particulate'').
? The analytical method used to measure removal in the
challenge test must discretely quantify the specific challenge
particulate. The maximum allowable feed water concentration of the
challenge particulate used during a challenge test is 10,000 times the
analytical method detection limit of the challenge particulate in the
filtrate.
? During challenge testing, filters must be operated at the
maximum design flow rate and for a duration sufficient to reach the
maximum design pressure drop (i.e., ``terminal pressure drop''). PWSs
may not operate bag or cartridge filters outside of these design
parameters during routine use. In order to achieve terminal pressure
drop during challenge testing, adding particulate matter, such as fine
carbon test dust or bentonite clay particles, to the test water is
allowed and may be necessary.
? In each challenge test, the removal of the challenge
particulate must be measured during three periods over the

[[Page 701]]

filtration cycle: (1) Within two hours of start-up of a new filter, (2)
when the pressure drop is between 45 and 55 percent of the terminal
pressure drop, and (3) when the pressure drop has reached 100 percent
of the terminal pressure drop. A log removal value (LRV) must be
calculated for each of these periods as follows: LOG₁₀
(filter influent challenge particulate level) - LOG₁₀
(filter effluent challenge particulate level). For each filter tested,
the LRV for the filter (LRV_filter) is equal to the minimum
of these three LRVs.
? The LRV_filter values for each filter that is
tested are used to determine the removal efficiency that is assigned to
the specific bag or cartridge filter product (i.e., a filter product
line) or combination of filters in series. If fewer than twenty filters
are tested, the removal efficiency of the filter product line is equal
to the lowest LRV_filter among the filters tested (today's
rule does not specify a minimum number of filters to test). If twenty
or more filters are tested, the removal efficiency of the filter
product line is equal to the 10th percentile of the
LRV_filter values among the filters tested.
? The Cryptosporidium treatment credit assigned to an
individual bag or cartridge filter is equal to the removal efficiency
established during challenge testing minus a 1.0-log factor of safety,
up to a maximum treatment credit of 2.0-log (e.g., if challenge testing
demonstrates a removal efficiency of 3.0-log or greater, the filter is
eligible to receive 2.0-log Cryptosporidium treatment credit).
? The Cryptosporidium treatment credit assigned to
configurations of two or more bag or cartridge filters operated in
series is equal to the removal efficiency established during challenge
testing minus a 0.5-log factor of safety, up to a maximum treatment
credit of 2.5-log (e.g., if challenge testing demonstrates a removal
efficiency of 3-log or greater, the filter receives 2.5-log
Cryptosporidium treatment credit).
If a previously tested bag or cartridge filter is modified in a
manner that could change the removal efficiency of the filter product
line, a new removal efficiency must be established for the modified
filter through challenge testing. If approved by the State, data from
challenge testing conducted prior to promulgation of today's rule may
be considered in lieu of additional testing. However, the prior testing
must have been conducted in a manner that demonstrates a removal
efficiency for Cryptosporidium commensurate with the treatment credit
awarded to the filter.
b. Background and Analysis
Bag and cartridge filters are widely used by very small PWSs and in
point-of-entry applications to remove particulate material from raw
water, including microbial pathogens like Cryptosporidium. Depending on
water quality and treatment plant infrastructure, these filters may be
used as the sole filtration step or as a polishing filter that follows
primary filtration processes. A critical aspect of bag and cartridge
filters as defined in today's rule is that they cannot undergo direct
integrity testing, which is used to detect leaks that could result in
contamination of the treated water. Cartridge filters that meet the
definition of a membrane process and can be direct integrity tested are
considered membranes under today's rule, and these are described in
section IV.D.11.
The Stage 2 M-DBP Advisory Committee recommended Cryptosporidium
treatment credits of 1.0- and 2.0-log for bag and cartridge filters,
respectively (USEPA 2000a), and the August 11, 2003 LT2ESWTR proposal
included criteria for PWSs to receive these treatment credits. The
proposed criteria required challenge testing and the application of a
1.0-log factor of safety to establish treatment credit. In today's
final rule, EPA has modified these criteria to allow both bag and
cartridge filters to be eligible for 2.0-log credit and to allow 2.5-
log credit with a 0.5-log factor of safety for bag or cartridge filters
operated in series. The following discussion summarizes the basis for
these criteria and for differences between the proposal and today's
final rule.
In the proposal, EPA reviewed bag and cartridge filtration studies
by Long (1983), Schaub et al. (1993), Goodrich et al. (1995), Ciardelli
(1996a and 1996b), Li et al. (1997), Roessler (1998), Enriquez et al.
(1999), NSF (2001a and 2001b), and Cornwell and LeChevallier (2002).
Results from these studies indicated that both bag and cartridge
filters exhibit variable removal efficiency, ranging from 0.5- to 3.6-
log. No correlation between the pore size rating established by the
manufacturer and the removal efficiency of the filter was apparent.
Additionally, available data did not indicate a strong relationship
between commonly used process monitoring parameters, such as turbidity
and pressure drop, and Cryptosporidium removal efficiency.
Due to this lack of correlation between either design criteria or
process monitoring and removal efficiency, today's rule requires
challenge testing of filters to establish Cryptosporidium treatment
credit. Challenge testing must measure the removal across the filter of
Cryptosporidium or a surrogate, like polystyrene microspheres, that is
removed no more efficiently than Cryptosporidium (Long 1983, Li et al.
1997, NSF 2002b). Further, because studies have shown the removal
efficiency of some bag and cartridge filters to decrease over the
course of a filtration cycle (Li et al. 1997, NSF 2001a,b), challenge
testing must assess removal efficiency during three periods: within two
hours of startup of a new filter, between 45-55 percent of terminal
pressure drop, and at the end of the run after terminal pressure drop
is realized.
Bag and cartridge filter challenge testing is product-specific and
not site-specific since the intent of this testing is to demonstrate
the removal capabilities of the filtration device rather than evaluate
the feasibility of implementing the technology at a specific plant.
Challenge testing must be conducted using full-scale filter elements to
assess the performance of the entire unit, including the filtration
media, seals, filter housing and other components integral to the
filtration system. To be eligible for treatment credit when operated in
series, filters must be tested in series. Multiple filters of the same
type can be tested to provide a better statistical basis for estimating
removal efficiency. The Toolbox Guidance Manual provides information on
bag and cartridge filter challenge testing.
Today's rule establishes the proposed requirement that a 1.0-log
factor of safety be applied to the removal efficiency established
during challenge testing for individual bag or cartridge filters when
determining treatment credit. Thus, to receive a 2.0-log treatment
credit, a removal efficiency of at least 3.0-log must be demonstrated
during challenge testing. EPA believes that this factor of safety is
necessary because integrity testing with bag and cartridge filters is
not possible (note: under today's rule, cartridge filters that can be
integrity tested are classified as membranes and no safety factor is
required; see section IV.D.11).
Challenge testing provides an estimate of the removal efficiency of
a bag or cartridge filter product line but does not involve testing
every filter. Further, it does not fully capture the variation in
filter performance that will occur over time during routine use. For
membranes, the use of direct integrity tests, such as a pressure hold
test, that is correlated to removal efficiency addresses this problem.
With bag and cartridge filters, however, EPA is aware

[[Page 702]]

of no equivalent test, and parameters like turbidity and pressure
differential that may be monitored with these filters have not been
shown to correlate with Cryptosporidium removal efficiency.
Consequently, a safety factor is necessary to account for variation in
individual filter performance relative to challenge test results.
Individual bag and cartridge filters are eligible for a maximum
Cryptosporidium treatment credit of 2.0-log. EPA proposed this level of
credit for cartridge filters but proposed a 1.0-log maximum credit for
bag filters, as recommended by the Advisory Committee. However, after
further reviewing available data, EPA has concluded that treatment
studies do not support establishing different limits on treatment
credit for bag and cartridge filters. Accordingly, today's rule treats
bag and cartridge filters equivalently. EPA continues to believe that
2.0-log is an appropriate maximum treatment credit for a single bag or
cartridge filter, based on available data on the removal of
Cryptosporidium and surrogates by these processes and the absence of a
direct integrity test.
Today's rule also establishes criteria for awarding treatment
credit to bag or cartridge filters operated in series. EPA believes
that the use of these filters in series provides clear advantages in
comparison to operation of a single filter. Series operation will
achieve both greater removal efficiency and improved reliability by
lessening the impact of variation in the performance of a single
filter. In consideration of these factors, bag or cartridge filters
operated in series are eligible for a higher Cryptosporidium treatment
credit of 2.5-log and require a lower safety factor of 0.5-log applied
to challenge test results when determining treatment credit.
c. Summary of Major Comments
In response to the August 11, 2003 proposal, EPA received
significant public comment on the following issues related to bag and
cartridge filtration: the allowable treatment credit, the factor of
safety applied to challenge testing results to determine treatment
credit, and the procedure for determining the removal efficiency. A
summary of these comments and EPA's responses follows.
In regard to the proposed treatment credits, several commenters
recommended that bag and cartridge filters should be eligible for up to
2.0- and 2.5-log credit, respectively, if supported by the challenge
test results. Others commented that filters should be allowed to
qualify for removal credits at or below the 1.0- and 2.0-log credits in
the proposal. EPA agrees that additional flexibility should be provided
with respect to the removal credit awarded to bag and cartridge
filters. After reviewing these comments and reassessing data presented
in the proposal on the removal efficiencies of bag and cartridge
filters, EPA revised the proposal to allow up to 2.0-log treatment
credit for either a single bag or cartridge filter. In addition,
today's rule allows up to 2.5-log credit for bag or cartridge filters
operated in series.
With respect to the 1.0-log safety factor applied to challenge test
results to determine treatment credit, some commenters supported this
approach, while others recommended a reduced safety factor. In
response, EPA continues to believe that a 1.0-log safety factor is
appropriate to address variability in individual filter performance and
in the absence of a direct integrity test for bag and cartridge
filters. Where filters are operated in series, however, EPA agrees that
the safety factor should be reduced. Series operation provides an
intrinsic process safety and will dampen some of the variability in
removal efficiency observed for individual filters. Thus, EPA is
reducing the factor of safety to 0.5-log for configurations consisting
of two or more filters in series.
Commenters requested that EPA clarify the procedure used to
determine the removal efficiency of bag and cartridge filters. In
response, expanded and clarified guidance on conducting challenge tests
to determine removal efficiency for bag and cartridge filters has been
included in the Toolbox Guidance Manual.
11. Membrane Filtration
a. Today's Rule
Today's final rule establishes criteria for awarding
Cryptosporidium treatment credit to membrane filtration processes. To
receive removal credit, filters must meet the definition of a membrane
filtration process and undergo challenge testing to establish removal
efficiency; PWSs must periodically verify system integrity through
direct integrity testing and perform continuous indirect integrity
monitoring during use. The removal credit awarded to a membrane process
is based on the removal efficiency demonstrated during challenge
testing and the sensitivity of the direct integrity test.
For the purpose of today's rule, membrane filtration is defined as
a pressure or vacuum driven separation process in which particulate
matter larger than 1 micrometer is rejected by an engineered barrier,
primarily through a size-exclusion mechanism, and which has a
measurable removal efficiency of a target organism that can be verified
through the application of a direct integrity test.

Membrane Challenge Testing

Any membrane filter used to meet the treatment requirements of
today's rule must undergo challenge testing to determine its
Cryptosporidium removal efficiency. Challenge testing establishes the
maximum Cryptosporidium treatment credit a membrane filtration process
is eligible to receive, provided this value is less than or equal to
the sensitivity of the direct integrity test, as described later in
this section. Challenge testing for membranes is product-specific, and
PWSs that install membranes that have successfully undergone challenge
testing are not required to repeat testing at their sites. Membrane
challenge testing must meet the following criteria:
? Challenge testing must be conducted on either an identical
full-scale module or a smaller-scale module identical in material and
similar in construction to the membrane modules the PWS will use. A
module is the smallest component of a membrane unit in which a specific
membrane surface area is housed in a device with a filtrate outlet
structure.
? Either Cryptosporidium or a surrogate that is removed no
more efficiently than Cryptosporidium must be used as the challenge
particulate during challenge testing.
? The analytical method used to measure removal in the
challenge test must discretely quantify the specific challenge
particulate. The maximum allowable feed water concentration used during
a challenge test is 6.5-log (3.16 x 10\6\) times the detection limit of
the challenge particulate in the filtrate.
? Challenge testing must be conducted under representative
hydraulic conditions at the maximum design flux and maximum design
process recovery as specified by the manufacturer for the membrane
filtration process. Flux is defined as the throughput of a pressure
driven membrane process expressed as flow per unit of membrane area.
Recovery is defined as the volumetric percent of feed water that is
converted to filtrate over the course of an operating cycle
uninterrupted by events such as chemical cleaning or a solids removal
process (i.e., backwashing).
? The removal efficiency for the membrane is determined from
the results of the challenge test, expressed as a log removal value
(LRV). A LRV must be calculated for each membrane module evaluated
during the challenge

[[Continued on page 703]]

Notices For
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994

National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule

Local Navigation