Joint NRC/EPA
Sewage Sludge Radiological Survey:
Survey Design and Test Site Results: C. Survey Design
The objectives of this joint NRC/EPA sewage
sludge/ash survey are to:
obtain data on the levels of radioactive materials in
sludge and ash at POTWs from across the country
estimate the extent to which radioactive contamination
comes from either NRC/State licensees or naturally-occurring
radioactivity
support potential rulemaking decisions by NRC or EPA,
if necessitated by the survey results.
However, because of the design limitations, the survey alone
may not be sufficient for rulemaking. These limitations include:
it is a voluntary survey
a small number of samples are collected at each POTW
the samples are collected in a snapshot in time, and
the survey is biased to POTWs associated with facilities
with the greatest potential to discharge radionuclides and
to POTWs in areas of higher concentrations of naturally-occurring
radioactive material (NORM).
Therefore, the survey results will not be a statistically
valid representation of radionuclide levels in sludges nationwide.
The survey consists of two components - a questionnaire and
a program to sample and analyze sewage sludge and incinerator
ash.
Development of the Questionnaire
NRC and EPA developed a questionnaire (Appendix
A) to request information from POTWs, such as their
sludge treatment processes and disposal practices. The questionnaire
also requests the zip codes for their collection systems
so NRC can identify the licensees associated with each POTW.
NRC will request from each Agreement State a list of licensees
for the zip codes associated with each POTW. In 1996, the
questionnaire was sent to nine test sites to assess the
questions and to obtain a better basis for estimating the
actual cost (burden hours) to the POTWs.
POTWs That Were Selected to Receive the Questionnaire in
sewage sludge and ash at POTWs across the United States
(the 50 States, the District of Columbia, and Puerto Rico).
To maximize its effectiveness, the survey will focus on
the POTWs associated with licensees with the greatest potential
to discharge radioactive material to the sanitary sewer
and POTWs in areas known to have high levels of naturally-occurring
isotopes such as radium, thorium, and uranium. With these
objectives in mind, the list of POTWs to be sent the questionnaire
was developed as follows:
Select POTWs associated with NRC and Agreement State
licensees that have the greatest potential for discharge.
NRC developed a list of licensees that have the greatest
potential for discharge, and EPA established a list of
POTWs associated with these licensees.
Select POTWs in areas known to have higher concentrations
of NORM in ground and surface water, or that are associated
with facilities that may potentially discharge NORM into
the sewage collection system.
Include POTWs with incinerators because radioactive
materials are expected to be at higher concentrations
in ash than in sludge. There are about 180 POTWs with
active incinerators. However, the number of POTWs with
incinerators varies from State to State, and if all the
incinerators are sampled, some States will include a disproportionately
high number of samples. For these reasons, the survey
plans to sample no more than a few POTWs with incinerators
in each State.
Ensure that the POTWs on the list developed in Steps
1 and 2 are from all geographic areas of the United States
(Coastal Plain, Appalachians, etc.) to reflect the regional
differences in NORM. If the list developed in Steps 1
and 2 has only a few POTWs in any of the geographic areas,
add POTWs from the 479 POTWs which responded to the questionnaire
in the first EPA national survey, which was conducted
in the late 1980's. The list of POTWs from the 1980's
survey was chosen because it includes POTWs for various
flow rates, percent industrial flow, and use and disposal
practices and is a group of nationally representative
POTWs.
Add POTWs requested by other ISCORS members and the
States.
Include a small group of POTWs with low potential for
elevated radioactive materials for comparison purposes.
NRC and EPA will jointly send the questionnaire to about
600 POTWs. The Association of Metropolitan Sewerage Agencies
and the Water Environment Federation will provide a letter
to be included with the questionnaire and will send a guidance
document prepared by the National Biosolids Partnership
(1999) and regulatory alert to the POTWs preceding the mailing
of the questionnaires to help introduce the POTWs to the
voluntary survey effort and provide assistance in conducting
radiation surveys of their treatment facilities and industrial
contributors.
The POTWs will be requested to voluntarily complete and
return the completed questionnaires to NRC. NRC will then
develop the list of licensees associated with each POTW
from the zip codes in their collection system and assign
each POTW to a geographic area. This information will be
entered into an electronic database so that NRC and EPA
can select the POTWs to be sampled. NRC will send letters
to the POTWs that returned the questionnaire with lists
of licensees in their service area. NRC will also develop
a sample return tracking system to follow up on non-respondents.
Selection of POTWs for Sampling and Analysis
From the responses to the questionnaire, about 300 POTWs
will be chosen for sampling and analysis. Based on the responses
to the questionnaires, the POTWs will be assigned to the
categories listed below. A number of POTWs will be sampled
from each category. The actual number of samples to be taken
from each category will be determined based on the responses
to the questionnaire. It is the goal of this survey to obtain
a representative number of POTWs from each category during
the course of the survey. It is recognized that some factors,
such as seasonality, may need to be studied further.
Type of NRC/Agreement State licensees that could dispose
into the sewage collection system
1. Academic
2. Medical
3. Manufacturing and Distribution
4. Research and Development
5. Other licensees
6. No licensees that discharge to the sewage collection
system
Geographic area
1. Coastal Plain
2. Appalachians
3. North Central
4. Central
5. Rockies and Basin and Range
6. Colorado Plateau
7. California
8. Pacific Northwest, Alaska, Hawaii
Sample Collection and Analysis
The sampling will take place over a one-year period. In
areas of high NORM, sampling may be adjusted during some
seasons, because there may be seasonal effects to the concentrations
of NORM at POTWs.
Each month, over a one-year period, NRC and EPA will jointly
send the NRC contractor a list of the POTWs to be sent letters
and sample collection materials. The NRC contractor will
contact the POTW operators to review the sampling instructions
and then mail the letters and sample collection packages
to the POTWs. Since POTWs routinely take representative
sludge and ash samples to monitor pollutants, the POTWs
will use similar procedures to collect samples for this
survey. The POTWs will return their samples to the NRC contractor
who will assign a code to each POTW to ensure confidentiality.
It is assumed that each POTW will, on average, send two
samples of processed sludges and/or ashes, so the total
number of samples collected from all POTWs participating
in the survey will be about 600. It is expected that each
laboratory will analyze about 300 samples.
The physical sampling and analysis procedure that will
be used in this survey is described in the Quality Assurance
Project Plan for this project. All analyses will be performed
using methods typically used for environmental monitoring
samples. All the samples will receive gamma spectroscopy,
gross alpha, and gross beta analyses. The gross alpha and
beta analyses are considered screening analyses. To use
resources most efficiently, additional isotope-specific
analyses will only be performed on samples with the highest
expected concentrations of the isotopes. Each month about
ten percent of the samples (about 2 or 3 samples at each
lab) will receive additional isotope-specific alpha or beta
analysis; the action level for this additional analysis
will be chosen based on the highest observed gross alpha
and gross beta results from the survey samples analyzed
that month.
Additional isotope-specific analysis will be conducted
for the following radioactive materials:
Radium, thorium and uranium are naturally-occurring radioactive
materials. Uranium and plutonium are also found in the effluents
from processes in nuclear facilities that are used to produce
nuclear fuel for research or power reactors. Strontium is
a medical isotope. Plutonium will be analyzed only for POTWs
with fuel-cycle or weapons research and development facilities
in the collection system. Carbon-14 is both naturally occurring
and man-made and is discharged by radiopharmaceutical and
research facilities. Tritium is discharged by academic,
manufacturing, and weapons research and development facilities.
During the survey, the laboratories will send the analysis
results to the ISCORS Sewage Subcommittee in individual
monthly letter reports that discuss the samples analyzed
that month and report any lab or field problems. The reviews
of these monthly letter reports could lead to changes in
the analysis procedures or in the selection of POTWs to
be sampled.
An NRC contractor will enter the sample analysis results
into an electronic data base and analyze the results. The
ISCORS Sewage Subcommittee has formed a working group to
perform dose modeling studies to help evaluate the potential
risks associated with the radioactive materials measured
in the survey. At the conclusion of the sample analyses,
the laboratories will report their results to the subcommittee
in a final report. The ISCORS Sewage Subcommittee will prepare
a final report on the survey results.
