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National Emission Standards for Hazardous Air Pollutants: Chlorine and Hydrochloric Acid Emissions From Chlorine Production
Note: EPA no longer updates this information, but it may be useful as a reference or resource.
[Federal Register: July 3, 2002 (Volume 67, Number 128)]
[Proposed Rules]
[Page 44713-44719]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr03jy02-28]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 63
[FRL-7229-6]
National Emission Standards for Hazardous Air Pollutants:
Chlorine and Hydrochloric Acid Emissions From Chlorine Production
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed decision not to regulate.
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SUMMARY: EPA proposes not to regulate chlorine and hydrochloric acid
(HCl) emissions for the Chlorine Production source category. We have
determined that no further control is necessary because chlorine and
HCl have well-defined health thresholds, and chlorine and HCl air
emissions from chlorine producers result in human exposures in the
ambient air that are below the threshold values with an ample margin of
safety. This notice does not address mercury emissions from mercury
cell chlor-alkali plants. Those emissions are addressed in a separate
action in the proposed rule section of this Federal Register.
DATES: Comments. Submit comments on or before September 3, 2002.
Public Hearing. If anyone contacts the EPA requesting to speak at a
public hearing by July 23, 2002, a public hearing will be held on
August 2, 2002.
ADDRESSES: Comments. By U.S. Postal Service, send comments (in
duplicate if possible) to: Air and Radiation Docket and Information
Center (6102), Attention Docket Number A-2002-09, U.S. EPA, 1200
Pennsylvania Avenue, NW, Washington, DC 20460. In person or by courier,
deliver comments (in duplicate if possible) to: Air and Radiation
Docket and Information Center (6102), Attention Docket Number A-2002-
09, U.S. EPA, 401 M Street, SW., Washington, DC 20460.
Public Hearing. If a public hearing is held, it will be held at the
new EPA facility complex in Research Triangle Park, North Carolina.
Docket. Docket No. A-2002-09 contains supporting information used
in developing the notice of proposed action for the Chlorine Production
source category. The docket is located at the U.S. EPA, 401 M Street,
SW., Washington, DC 20460 in Room M-1500, Waterside Mall (ground
floor), and may be inspected from 8:30 a.m. to 5:30 p.m., Monday
through Friday, excluding legal holidays.
FOR FURTHER INFORMATION CONTACT: Mr. Iliam Rosario, Metals Group,
Emission Standards Division (C439-02), U.S. EPA, Research Triangle
Park, North Carolina 27711, telephone number: (919) 541-5308,
facsimile: (919) 541-5600, electronic mail address:
rosario.iliam@epa.gov.
SUPPLEMENTARY INFORMATION: Comments. Comments and data may be submitted
by electronic mail (e-mail) to: a-and-r-docket@epa.gov. Electronic
comments must be submitted as an ASCII file to avoid the use of special
characters and encryption problems and will also be accepted on disks
in WordPerfect format. All comments and data submitted in electronic
form must note the docket number: Docket No. A-2002-09. No confidential
business information (CBI) should be submitted by e-mail. Electronic
comments may be filed online at many Federal Depository Libraries.
Commenters wishing to submit proprietary information for
consideration must clearly distinguish such information from other
comments and clearly label it as CBI. Send submissions containing such
proprietary information directly to the following address, and not to
the public docket, to ensure that proprietary information is not
inadvertently placed in the docket: OAQPS Document Control Office
(C404-02), Attention: Iliam Rosario, Metals Group, Emission Standards
Division, U.S. EPA, Research Triangle Park, NC 27711. The EPA will
disclose information identified as CBI only to the extent allowed by
the procedures set forth in 40 CFR part 2. If no claim of
confidentiality accompanies a submission when it is received by the
EPA, the information may be made available to the public without
further notice to the commenter.
Public Hearing. Persons interested in presenting oral testimony or
inquiring as to whether a hearing is to be held should contact Cassie
Posey, telephone number: (919) 541-0069. Persons interested in
attending the public hearing must also call Cassie Posey to verify the
time, date, and location of the hearing. The public hearing will
provide interested parties the opportunity to present data, views, or
arguments concerning the proposed emission standards.
Docket. The docket is an organized and complete file of all the
information considered by the EPA in rule development. The docket is a
dynamic file because material is added throughout the rulemaking
process. The docketing system is intended to allow members of the
public and industries involved to readily identify and locate documents
so that they can effectively participate in the rulemaking process.
Along with the proposed and promulgated standards and their preambles,
the contents of the docket will serve as the record in the case of
judicial review. (See section 307(d) (7)(A) of the Clean Air Act
(CAA).) The materials related to this notice of proposed action are
available for review in the docket or copies may be mailed on request
from the Air Docket by calling (202) 260-7548. A reasonable fee may be
charged for copying docket materials.
WorldWide Web (www) Information. In addition to being available in
the docket, an electronic copy of today's notice of proposed action
will also be available through EPA's www site. Following signature, a
copy of the rule will be posted on our policy and
[[Page 44714]]
guidance page for newly proposed or promulgated rules: http://
www.epa.gov/ttn/oarpg. The web site provides information and technology
exchange in various areas of air pollution control. If more information
regarding the web site is needed, call our web site help line at (919)
541-5384.
Regulated entities. Entities potentially affected by this action
include facilities engaged in the production of chlorine. Affected
categories and entities include those sources listed in the primary
Standard Industrial Classification code 2812 or North American
Information Classification System code 325181.
This description is not intended to be exhaustive, but rather
provides a guide for readers regarding entities likely to be affected
by this action. If you have questions regarding the applicability of
this action to a particular entity, consult the person listed in the
preceding FOR FURTHER INFORMATION CONTACT section.
Outline. The information presented in this preamble is organized as
follows:
I. Background
A. What is the source of authority for development of NESHAP?
B. What is the source category?
C. What are the health effects of chlorine and hydrogen
chloride?
II. Summary of Proposed Action
III. Rationale for Proposed Action
A. What is our statutory authority under section 112(d)(4)?
B. What is the basis for our proposed action?
IV. Solicitation of Comments and Public Participation
I. Background
A. What Is the Source of Authority for Development of NESHAP?
Section 112 of the CAA contains our authority for reducing
emissions of hazardous air pollutants (HAP). Section 112(d) requires us
to promulgate regulations establishing emission standards for each
category or subcategory of major sources and area sources of HAP listed
pursuant to section 112(c). Section 112(d)(2) specifies that emission
standards promulgated under the section shall require the maximum
degree of reductions in emissions of the HAP subject to section 112
that are deemed achievable considering cost and any non-air quality
health and environmental impacts and energy requirements.
National emission standards for hazardous air pollutants (NESHAP)
reflect the maximum degree of reduction in emissions of HAP that is
achievable. This level of control is commonly referred to as maximum
achievable control technology (MACT).
The CAA includes exceptions to the general statutory requirement to
establish emission standards based on MACT. Section 112(d)(4) allows us
to use discretion in developing risk-based standards for HAP ``for
which a health threshold has been established'' provided that the
standards achieve an ``ample margin of safety.''
B. What Is the Source Category?
The Chlorine Production source category was initially listed as a
major source of HAP pursuant to section 112(c)(1) of the CAA on July
16, 1992 (57 FR 31576). At the time of the initial listing, we defined
the Chlorine Production source category as follows:
* * * The Chlorine Production Source Category includes any
facility engaged in the production of chlorine. The category
includes, but is not limited to, facilities producing chlorine by
the following production methods: diaphragm cell, mercury cell,
membrane cell, hybrid fuel cell, Downs cell, potash manufacture,
hydrochloric acid decomposition, nitrosyl chloride process, nitric
acid/salt process, Kel-Chlor process, and sodium chloride/sulfuric
acid process.
We know of no facilities that produce chlorine using hybrid fuel
cells, the nitrosyl chloride process, the Kel-Chlor process, the sodium
chloride/sulfuric acid process, or as a by-product from potash
manufacturing. We have identified 45 facilities that produce chlorine
using mercury cells, diaphragm cells, or membrane cells. Collectively,
these facilities are referred to as chlor-alkali plants as they produce
chlorine and alkali (sodium hydroxide) as co-products.
We have also identified three facilities that produce chlorine as a
by-product: one from the production of sodium metal in Downs cell,
another from the production of potassium nitrate fertilizer that uses
the nitric acid/salt process, and a third that produces chlorine as a
by-product from primary magnesium refining. In addition, we have
identified a resin producer that produces chlorine both in a chlor-
alkali plant and through the decomposition of HCl.
Of the 48 facilities that produce chlorine, we have identified 21
that are major sources, including 20 chlor-alkali plants and the one
primary magnesium refining facility. The primary magnesium refining
facility is itself a major source emitting on the order of 600 tons of
chlorine and 3,000 tons of HCl yearly, and is, in fact, a separately
listed source category. As such, it will be addressed on its own in a
separate rulemaking.
None of the 20 chlor-alkali plants are major in and of themselves,
but are major due to collocation. That is, they are part of a larger
contiguous establishment that is a major source. These larger
establishments include organic chemical manufacturers, polymer and
resin producers, and pulp and paper mills, all of which are already
subject to one or more NESHAP. For instance, the organic chemical
manufacturers are subject to the Hazardous Organic NESHAP, or HON (40
CFR part 63, subparts F, G, and H). The HON is a comprehensive rule
that covers process vent, transfer, storage tank, equipment leak and
wastewater emissions from the production of almost 400 organic
chemicals. More than 100 organic HAP are regulated under the HON.
Polymers and resins producers are subject to four separate NESHAP
(40 CFR part 63, subparts U, W, JJJ, and OOO) and must control process
vent, transfer, storage tank, equipment leak and wastewater emissions.
Chlor-alkali facilities that are collocated with pulp and paper mills
are covered by 40 CFR part 63, subpart S (Pulp and Paper MACT III) and
40 CFR part 63, subpart KK (Printing and Publishing MACT). Chlor-alkali
production facilities are also collocated with the following source
categories: hazardous waste pesticide active ingredients production
(subject to 40 CFR part 63, subpart MMM), polyether polyols production
(subject to 40 CFR part 63, subpart PPP), and polycarbonates production
(subject to 40 CFR part 63, subpart YY). There is also the
Miscellaneous Organic Chemical Products and Processes NESHAP, currently
under development, which will cover a variety of smaller, specialty
chemical manufacturing processes, many that utilize chlorine.
Therefore, most major processes at the sites where chlor-alkali
facilities are located are subject to, or will be subject to, NESHAP to
reduce HAP emissions. In addition to NESHAP, the chlorine production
facilities are themselves subject to rules pursuant to section 112(r)
of the CAA for the prevention of accidental releases of chemicals (40
CFR part 68).
The primary HAP emitted from chlorine production facilities
processes are chlorine and HCl.\1\ In each of the three chlor-alkali
electrolytic cell processes, an electric current is passed through a
salt solution (brine) causing the dissociation of salt to produce
[[Page 44715]]
chlorine gas and an alkaline solution. Chlorine is collected from the
cell room and is cooled, dried, and condensed in the purification
process. The dried, gaseous chlorine then may be cooled further and
compressed and liquified using multiple-stage condensers in the
compression/liquefaction operation. Chlorine can be emitted from the
tail gas stream from the final liquefier, the cell room, and equipment
in chlorine service. Hydrochloric acid is used to pretreat feed brine
prior to entering a chlor-alkali cell and at other locations throughout
the process to adjust pH. It can also be emitted from storage tanks and
equipment in HCl service.
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\1\ The mercury cell chlor-alkali process also emits mercury.
Those emissions are addressed in a separate proposal elsewhere in
today's Federal Register.
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Since chlor-alkali processes produce both chlorine and hydrogen, it
is common for a direct synthesis HCl production unit to be incorporated
into a chlor-alkali facility. This is the situation at four of the 20
chlor-alkali facilities at major source plant sites. In the direct
synthesis process, chlorine and hydrogen are burned together to produce
HCl. The gaseous HCl stream is then routed to an absorber and
concentrated to produce a liquid HCl product. In many instances at
chlor-alkali facilities, gaseous chlorine-containing waste streams
(such as the tail gas from the liquifiers) provide chlorine to the HCl
production unit. Therefore, we consider these direct synthesis HCl
production units to be a part of the chlor-alkali facilities. These
direct synthesis HCl production units can emit HCl from the absorber
vent and associated storage vessels and transfer racks.
C. What Are the Health Effects of Chlorine and Hydrogen Chloride?
Acute (short-term) exposure to high levels of chlorine in humans
can result in chest pain, vomiting, toxic pneumonitis, and pulmonary
edema. At lower levels, chlorine is a potent irritant to the eyes, the
upper respiratory tract, and lungs. Chronic (long-term) exposure to
chlorine gas in workers has resulted in respiratory effects including
eye and throat irritation and airflow obstruction. Animal studies have
reported decreased body weight gain, eye and nose irritation, non-
neoplastic nasal lesions, and respiratory epithelial hyperplasia from
chronic inhalation exposure to chlorine. No information is available on
the carcinogenic effects of chlorine in humans from inhalation
exposure. We have not classified chlorine for potential
carcinogenicity.
Hydrogen chloride is corrosive to the eyes, skin, and mucous
membranes. Acute inhalation exposure may cause eye, nose, and
respiratory tract irritation and inflammation and pulmonary edema in
humans. Chronic occupational exposure to HCl has been reported to cause
gastritis, bronchitis, and dermatitis in workers. Prolonged exposure to
low concentrations may also cause dental discoloration and erosion. No
information is available on the reproductive or developmental effects
of HCl in humans. In rats exposed to HCl by inhalation, altered estrus
cycles have been reported in females and increased fetal mortality and
decreased fetal weight have been reported in offspring. We have not
classified HCl for carcinogenicity.
II. Summary of Proposed Action
We are proposing not to regulate chlorine and HCl emissions from
chlorine production processes. Under the authority of section
112(d)(4), we have determined that no further control is necessary
because chlorine and HCl are ``health threshold pollutants,'' and
chlorine and HCl levels emitted from chlorine production processes are
below their threshold values within an ample margin of safety. Further,
due to the fact that these two pollutants are the only HAP emitted in
significant quantities from chlorine production plants, we are
proposing not to develop any NESHAP for the Chlorine Production source
category, with the exception of a NESHAP for mercury emissions from
mercury cell chlor-alkali plants.
III. Rationale for Proposed Action
This section explains the statutory basis for considering health
thresholds when establishing standards, and the basis for today's
proposed action, including a discussion of the risk assessment
conducted to support the ample margin of safety decision.
A. What Is Our Statutory Authority Under Section 112(d)(4)?
As stated previously in this notice, section 112 of the CAA
includes exceptions to the general statutory requirement to establish
emission standards based on MACT. Of relevance here, section 112(d)(4)
allows us to develop risk-based standards for HAP ``for which a health
threshold has been established'' provided that the standards achieve an
``ample margin of safety.'' Therefore, we believe we have the
discretion under section 112(d)(4) to develop risk-based standards
which may be less stringent than the corresponding floor-based MACT
standards for some categories emitting threshold pollutants.
In deciding standards for this source category, we seek to assure
that emissions from every source in the category or subcategory are
less than the threshold level for an individual exposed at the upper
end of the exposure distribution. The upper end of the exposure
distribution is calculated using the ``high end exposure estimate,''
defined as a plausible estimate of individual exposure for those
persons at the upper end of the exposure distribution, conceptually
above the 90th percentile, but not higher than the individual in the
population who has the highest exposure. We believe that assuring
protection to persons at the upper end of the exposure distribution is
consistent with the ``ample margin of safety'' requirement in section
112(d)(4).
We emphasize that the use of section 112(d)(4) authority is wholly
discretionary. As the legislative history indicates, cases may arise in
which other considerations dictate that we should not invoke this
authority to establish less stringent standards, despite the existence
of a health effects threshold that is not jeopardized. For instance, we
do not anticipate that we would set less stringent ``risk-based''
standards where evidence indicates a threat of significant or
widespread environmental effects, although it may be shown that
emissions from a particular source category do not approach or exceed a
level requisite to protect public health with an ample margin of
safety. We may also elect not to set less stringent risk-based
standards where the estimated health threshold for a contaminant is
subject to large uncertainty. Thus, in considering appropriate uses of
our discretionary authority under section 112(d)(4), we consider other
factors in addition to health thresholds, including uncertainty and
potential ``adverse environmental effects,'' as that phrase is defined
in section 112(a)(7).
B. What Is the Basis for Our Proposed Action?
We are proposing in today's notice not to develop NESHAP for the
Chlorine Production source category other than the mercury standards
being proposed elsewhere in today's Federal Register for mercury cell
processes. This decision is based on the following. First, we consider
chlorine and HCl to be threshold pollutants. Second, we have defined
threshold values in the form of Inhalation Reference Concentrations
(RfC) and acute exposure guideline levels (AEGL). Third, chlorine and
HCl are emitted from chlorine production plants (in the absence of
additional control) in quantities that result in human exposure in the
ambient air at levels well below the threshold values with an ample
margin of safety. Finally, there are no adverse environmental
[[Page 44716]]
effects associated with these pollutants. The bases and supporting
rationale for these conclusions are provided in the following sections.
1. Threshold Pollutants
For the purposes of section 112(d)(4), several factors are
considered in our decision on whether a pollutant should be categorized
as a health threshold pollutant. These factors include evidence and
classification of carcinogenic risk and evidence of noncarcinogenic
effects. For a detailed discussion of factors that we consider in
deciding whether a pollutant should be categorized as a health
threshold pollutant, please see the April 15, 1998 Federal Register
document (63 FR 18766).
In the April 15, 1998 action cited above, we determined that HCl, a
Group D pollutant, is a health threshold pollutant for the purpose of
section 112(d)(4) of the CAA (63 FR 18753). We also believe that it is
reasonable to classify chlorine as a Group D pollutant. There have been
limited animal studies and observations of human occupational
inhalation exposure for chlorine. There has been no evidence of a
carcinogenic response in chronic, subchronic, or acute inhalation
exposures in laboratory animal studies or from occupational inhalation
exposure. Based on the limited negative carcinogenicity data, and on
our knowledge of how chlorine reacts in the body and its likely
mechanism of action, we presumptively consider chlorine to be a
threshold pollutant.
2. Health Effects Exposure Assessment
We conducted a risk assessment to determine whether the emissions
of chlorine and HCl from chlorine production plants at the current
baseline levels are in quantities that are below the threshold values
for chlorine and HCl within an ample margin of safety. The summary of
this assessment is organized as follows: (1) Hazard identification and
dose-response assessment, (2) emissions and release information, and
(3) exposure assessment.
It is important to note that the risk assessment methodology
applied here should not be interpreted as a standardized approach that
sets a precedent for how EPA will analyze application of section
112(d)(4) in other cases. The approach presented here, including
assumptions, models, and worst-case of sensitivity analysis, was
selected to meet the unique needs of this particular case, to provide
the appropriate level of detail and margin of safety given the data
availability, chemicals, and emissions particular to this category.
Hazard Identification and Dose-Response Assessment
The RfC is a ``long-term'' threshold, defined as an estimate of a
daily inhalation exposure that, over a lifetime, would not likely
result in the occurrence of noncancer health effects in humans. We have
determined that the RfC for HCl of 20 micrograms per cubic meter [mu]g/
m\3\) is an appropriate threshold value for assessing risk to humans
associated with exposure to HCl through inhalation (63 FR 18766, April
15, 1998). Therefore, we used this RfC as the threshold value in our
exposure assessment for HCl emitted from chlorine production plants.
We also considered using the RfC for chlorine. In cases where we
have not studied a chemical itself, we rely on the studies of other
governmental agencies, such as the Agency for Toxic Substances and
Disease Registry (ATSDR) or the Office of Health Hazard Assessment of
California's Environmental Protection Agency (CAL EPA), for RfC values.
The CAL EPA developed an RfC value of 0.2 [mu]g/m\3\ for chlorine based
on a large inhalation study with rats.
Since chlorine does not generally persist in the atmosphere, we
evaluated the appropriateness of using this chlorine RfC for this
assessment. Chlorine in the atmosphere photolyzes to chloride ions
(Cl-) and then quickly reacts with methane to form HCl in
bright sunshine. The estimated chlorine lifetime under these conditions
is approximately 10 minutes. Even though emissions of chlorine in the
absence of sunshine (e.g., at nighttime) remain as chlorine in the
atmosphere until sunlight emerges, we do not believe that use of the
chlorine RfC was appropriate for this assessment since long-term
exposure to significant levels of chlorine is unlikely. EPA requests
comments on the appropriateness of using a chlorine RfC to assess
impacts of long-term exposure in this case.
However, we did conclude that the health effects of the long-term
exposure to the HCl formed from the chlorine emitted from chlorine
production plants should be considered. Therefore, we calculated the
amount of HCl that would be formed from the emitted chlorine and used
the HCl RfC of 20 [mu]g/m\3\ for determining the long-term
noncarcinogenic effects of the chlorine emissions.
In addition to these effects of long-term inhalation of HCl, we
also considered whether thresholds for short-term exposure to chlorine
and HCl should be considered in this assessment. Acute exposure
guideline level toxicity values are estimates of adverse health effects
due to a single exposure lasting 8 hours or less. The confidence in the
AEGL (a qualitative rating or either low, medium, or high) is based on
the number of studies available and the quality of the data. Consensus
toxicity values for effects of acute exposures have been developed by
several different organizations, and we are beginning to develop such
values. A national advisory committee organized by the EPA has
developed AEGL for priority chemicals for 30-minute, 1-hour, 4-hour,
and 8-hour airborne exposures. They have also determined the levels of
these chemicals at each exposure duration that will protect against
discomfort (AEGL1), serious effects (AEGL2), and life-threatening
effects or death (AEGL3). Hydrogen chloride has been assigned a 1-hour
AEGL2 of 33,000 [mu]g/m\3\. Above this level, it is predicted that the
general population, including sensitive individuals (such as
asthmatics, children, or the elderly), could experience irreversible or
other serious, long-lasting adverse health effects, or an impaired
ability to escape. This value is a medium confidence value based on the
severe nasal or pulmonary histopathology observed in rats exposed to a
high concentration of 1,950,000 [mu]g/m\3\ HCl for 30 minutes. The
AEGL2 value for HCl is displayed in an EPA internal database, the Air
Toxics Health Effects Database (ATHED), as the appropriate value to use
in short-term modeling.
Chlorine has been assigned a 1-hour AEGL2 toxicity value of 5,800
[mu]g/m\3\. This value is based on a human inhalation exposure study
that included a sensitive individual, and this AEGL value has a high
confidence value (62 FR 58839). This AEGL2 value is also contained in
EPA's ATHED as the appropriate value to use in short-term modeling.
We used these AEGL values as threshold values for assessing the
inhalation health effects of short-term exposures to chlorine and HCl.
While chlorine does photolyze and eventually form HCl, we concluded
that it was appropriate to use the chlorine AEGL value of 5,800 [mu]g/
m\3\ for this assessment since it would be possible for individuals to
be exposed to chlorine for 1-hour periods at night or on cloudy days.
Emissions and Release Information
Under the authority of section 114, we collected chlorine and HCl
emissions information for all chlorine production facilities at the 20
major source sites.
[[Page 44717]]
Chlorine and HCl emissions were reported for point sources and fugitive
emissions from the chlorine production units at each site. For the four
sites where direct synthesis HCl production units are part of the
chlorine production facility, emissions were also reported.
Respondents provided maximum annual and hourly chlorine and HCl
emissions (typically, permitted emission rates were provided) and
release characteristics. According to the information submitted,
plantwide annual chlorine emissions from chlorine production processes
ranged from less than one kilogram per year to over 6 Megagrams per
year (Mg/yr). Of the 20 plant sites, 11 reported HCl emissions from
chlorine production (and for four sites, HCl production processes),
which ranged from less than one kilogram per year to around 32 Mg/yr.
The hourly plantwide chlorine emissions from chlorine production
processes ranged from less than 2 grams per hour (g/hr) to around 10
kilograms per hour (kg/hr). For the 11 sites reporting HCl emissions,
the hourly HCl emissions ranged from less than 1 g/hr to around 1 kg/
hr.
Ten of the plant sites did not report any fugitive emissions. We
believe that it is reasonable to expect that all chlorine production
facilities would have some fugitive emissions. Therefore, we developed
emission factors based on the reported fugitive emissions and related
capacities for those plant sites that did report fugitive emissions.
These factors ranged from 6.3 x 10--8 to 2.88 pounds per ton
of chlorine production capacity. We used the maximum emission factor to
conservatively estimate fugitive emissions for the 10 facilities that
did not report fugitive emissions.
The release characteristics needed for the dispersion model
included stack height, stack diameter, temperature, and exit velocity
for point sources. For approximately 98 percent of the point sources
reported, these parameters were provided in the section 114 responses.
If release characteristics were not provided, we assigned default
parameters based on data for the chlorine production industry in
national emission databases and other data reported in response to the
survey. The release characteristics needed for fugitive emission
sources are release height and area. Release heights were provided for
about 17 percent of the fugitive emission sources. For those fugitive
emission sources for which information on release heights were not
provided, we assumed that they were at 1 meter. No information was
provided regarding the area of the fugitive emission sources.
Therefore, we assumed an area of 2,000 square meters for every fugitive
emission source, which is a standard default used in modeling.
Exposure Assessment
The exposure assessment was conducted for chlorine and HCl
emissions from all chlorine production processes in the source category
(i.e., from the chlorine production processes at the 20 sites that are
major sources of HAP). As discussed above, the emissions data and
release characteristics provided directly from all 20 plants were used
as inputs to the assessment.
The Industrial Source Complex--Short Term Dispersion Model, Version
3 (ISCST3), was used for this exposure assessment. Receptors were
placed at the center of census blocks (based on the 2000 Census) within
2 kilometers of the site and in the population-weighted centers of
census block groups or census tracks out to 50 kilometers.
Meteorological data from the nearest representative meteorological
station were used. EPA requests comments on how to consider locations
of receptors in assessing potential impacts on an individual exposed at
the upper end of the exposure distribution for a large number of
diverse facilities.
To determine the impacts of long-term exposure to chlorine and HCl
emissions from chlorine plants, we used the maximum annual emission
values provided by the plants. As discussed above, we converted the
chlorine emissions to HCl since chlorine only persists in the
atmosphere for a short amount of time. Therefore, we modeled the annual
average HCl concentration at each receptor that was the result of the
combination of the HCl emissions and the chlorine emissions that were
converted to HCl through photolysis and subsequent reaction with
methane.
As noted earlier, ten of the plants did not report any fugitive
emissions. For these plants, we modeled the reported point source
emissions and then modeled the estimated fugitive emissions separately.
We added the highest concentration resulting from point source
emissions with the highest concentration resulting from the fugitive
emissions to obtain a conservative estimate of the highest HCl
concentration that would be expected.
The highest modeled annual average HCl concentration from any
chlorine production plant was 0.6 [mu]g/m\3\. This is less than 3
percent of the HCl RfC of 20 [mu]g/m\3\. Over 15 million people live in
the areas around these 19 plant sites. Of these people, only around
1,300 were exposed to annual average HCl concentrations greater than 1
percent of the RfC. In fact, well over 99 percent were exposed to
annual average HCl concentrations less than 0.1 percent of the RfC.
To determine the impacts of short-term exposures to chlorine and
HCl emissions from chlorine production plants, we used the maximum
hourly emission values provided by the plants and obtained the highest
individual hourly concentrations from the ISCST3 model. Separate runs
were conducted for chlorine and HCl. The same process described above
was used for plants that did not report any fugitive emissions.
The highest 1-hour chlorine concentration modeled was 346 [mu]g/
m\3\, which is less than 6 percent of the AEGL2 1-hour threshold value
for chlorine (5,800 [mu]g/m\3\). This highest 1-hour HCl modeled
concentration was 120 [mu]g/m\3\, which is less than 1 percent of the
AEGL2 1-hour threshold value for HCl (33,000 [mu]g/m\3\). We modeled
these short-term concentrations for 5 years for each plant, which means
concentrations were obtained for over 830,000 hours. Only around 75
hours (less than one hundredth of one percent) had modeled chlorine
concentrations greater than 5 percent of the AEGL2 value, and no hours
had modeled HCl concentrations greater than the AEGL2 value.
Given the fact that the highest modeled concentrations were so far
below the threshold values, we elected to primarily evaluate the
uncertainty and variability of this assessment qualitatively, coupled
with a few basic sensitivity analyses. These sensitivity analyses
focused on evaluating the uncertainties for the ``worst-case''
situations, as we were not concerned with uncertainties that resulted
in even lower estimated risks.
We identified four potential areas of uncertainty/ variability in
the exposure assessment described above. These are emissions, the fate
and transport model, exposure estimates, and toxicological dose
response. Each of these areas is briefly discussed in the following.
As emission rates increase, exposure and risk increase. As noted
earlier, the facilities reported maximum annual and maximum hourly
emission rates. Most often, the reported rates were the facility's
permitted emission rates. In addition, for those facilities that did
not report any fugitive emissions, we estimated and modeled fugitive
emissions based on the highest emission factor. Therefore, we would
expect actual emissions to be less than those modeled, and thus, we
believe that the results are biased high.
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The primary uncertainties identified that are associated with the
fate and transport modeling were the inherent uncertainty associated
with the trying to represent complex atmospheric processes with a
series of equations in the ISCST3 model (which is beyond the scope of
this assessment) and missing release parameters, particularly for
fugitive emission sources.
For the point sources, around 2 percent of the parameters were
missing. For each missing parameter, we assigned a default parameter
that was within the ranges provided by the other respondents. Since the
actual release characteristics could be either higher or lower than
these defaults, the results could be biased either way for this small
percentage of the point sources.
Release heights were only provided for 17 percent of the fugitive
emission sources, which ranged from 1.8 meters to 9.1 meters. For the
fugitive sources without heights provided, we used a default height of
1 meter, which is more conservative than any reported value. Therefore,
we anticipated that this could bias the results high.
There was considerable uncertainty associated with the size and
location of fugitive emission sources. We used a default area of 2,000
m\2\ for every fugitive emission source, with dimensions approximately
45 meters by 45 meters. This is a generic default value that we
typically use for modeling fugitive emission sources, and it is not
based on information provided by actual chlorine production facilities.
The southwest corner of this area was placed at the mid-point of the
locations for all reported point sources for the facility. The lack of
information regarding the true size and location of chlorine production
facilities could bias the concentration estimates high or low.
Uncertainty and variability also exist in the exposure estimates
and the toxicological dose response, most of which result in the
overestimation of risk. The RfC and AEGL2 values used in the
assessment, which were discussed above, may contain multiple
uncertainty factors whose impact is to add degrees of conservatism
resulting in an overestimation of noncancer effects. In addition, the
RfC assumes that individuals would be continuously exposed to the
modeled concentration. As we believe these factors would only decrease
the risk estimates, we did not evaluate their impact.
As noted above, our focus was only on those uncertainties that
might increase the risk estimates and, thus, impact our decision not to
regulate HCl and chlorine emissions from this source category. Of the
basic uncertainties discussed above, the factors that we believe could
result in underestimated HAP concentrations (and, therefore,
underestimated risks) include the default stack parameters for point
sources and the default size and location of the fugitive emission
sources.
We conducted a worst-case analysis for both long-term and short-
term exposures to evaluate the potential upper-end impact of these
uncertainties. For this analysis, we selected the single point source
location from all plants that resulted in the highest estimated
concentration people would be exposed to when run using a uniform
emission rate. We then modeled the highest total facility emissions
(maximum annual emissions for the long-term analysis and maximum hourly
emissions for the short-term analysis) of chlorine and HCl at that
point source location and used the most conservative stack parameters.
We then chose the highest of these totals for chlorine and for HCl to
put at the single point location. We also modeled a fugitive emission
source using the highest reported emission factor coupled with the
highest production capacity.
The results of this analysis show that, even with these worst-case
conditions, the modeled concentrations were well below the threshold
values. For the long-term impacts of the chlorine and HCl emissions
(modeled as HCl, as discussed previously), the highest modeled annual
HCl concentration was less than 5 [mu]g/m\3\, which is less than 23
percent of the HCl RfC. The highest modeled maximum 1-hour chlorine and
HCl concentrations were around 2,500 [mu]g/m\3\ and 230 [mu]g/m\3\,
respectively. These values represent around 44 percent of the 1-hour
chlorine AEGL2 threshold value and less than 1 percent of the 1-hour
HCl AEGL2.
3. Environmental Effects
The standards for emissions must also protect against significant
and widespread adverse environmental effects to wildlife, aquatic life,
and other natural resources. We did not conduct a formal ecological
risk assessment. However, we have reviewed publications in the
literature to determine if there would be reasonable expectation for
serious or widespread adverse effects to natural resources.
We consider the following aspects of pollutant exposure and
effects: Toxicity effects from acute and chronic exposures to expected
concentrations around the source (as measured or modeled), persistence
in the environment, local and long-range transport, and tendency for
bio-magnification with toxic effects manifest at higher trophic levels.
As discussed above, the evidence available to date indicates that
chlorine and HCl are threshold pollutants for the purposes of section
112(d)(4). Since chlorine is converted to HCl in the atmosphere, we did
not perform a separate evaluation of chlorine exposure in this
analysis.
No research has been identified for effects on terrestrial animal
species beyond that cited in the development of the HCl RfC. Modeling
calculations indicate that there is little likelihood of chronic or
widespread exposure to HCl at concentrations above the threshold around
chlorine production facilities. Based on these considerations, we
believe that the RfC can reasonably be expected to protect against
widespread adverse effects in other animal species as well.
Plants also respond to airborne HCl levels. Chronic exposure to
about 600 [mu]g/m\3\ can be expected to result in discernible effects,
depending on the plant species. Plants respond differently to HCl as an
anhydrous gas than to HCl aerosols. Relative humidity is important in
plant response; there appears to be a threshold of relative humidity
above which plants will incur twice as much damage at a given dose.
Effects include leaf injury and decrease in chlorophyll levels in
various species given acute, 20-minute exposures of 6,500 to 27,000
[mu]g/m\3\. A field study reports different sensitivity to damage of
foliage in 50 species growing in the vicinity of an anhydrous aluminum
chloride manufacturer. American elm, bur oak, eastern white pine,
basswood, red ash and several bean species were observed to be most
sensitive. Concentrations of HCl in the air were not reported. Chloride
ion in whole leaves was 0.2 to 0.5 percent of dry weight; sensitive
species showed damage at the lower value, but tolerant species
displayed no injury at the higher value. Injury declined with distance
from the source with no effects observed beyond 300 meters. Maximum
modeled long-term HCl concentrations (0.6 [mu]g/m\3\) are well below
the 600 [mu]g/m\3\ chronic threshold, and the maximum short-term HCl
concentration (346 [mu]g/m\3\) are far below the 6,500 [mu]g/m\3\ acute
exposure threshold. Therefore, no adverse exposure effects are
anticipated.
Prevailing meteorology strongly determines the fate of HCl in the
atmosphere. However, HCl is not considered a strongly persistent
pollutant, or one where long range transport is important in predicting
its ecological effects. In the atmosphere, HCl can be expected to be
absorbed into
[[Page 44719]]
aqueous aerosols, due to its great affinity for water, and removed from
the troposphere by rainfall. In addition, HCl will react with hydroxy
ions to yield water plus chloride ions. However, the concentration of
hydroxy ions in the troposphere is low, so HCl may have a relatively
long residence time in areas of low humidity. No studies are reported
of HCl levels in ponds or other small water bodies or soils near major
sources of HCl emissions. Toxic effects of HCl to aquatic organisms
would likely be due to the hydronium ion, or acidity. Aquatic organisms
in their natural environments often exhibit a broad range of pH
tolerance. Effects of HCl deposition to small water bodies and to soils
will primarily depend on the extent of neutralizing by carbonates or
other buffering compounds. Chloride ions are essentially ubiquitous in
natural waters and soils so minor increases due to deposition of
dissolved HCl will have much less effect than the deposited hydronium
ions. Deleterious effects of HCl on ponds and soils, where such effects
might be found near a major source emitting to the atmosphere, likely
will be local rather than widespread, as observed in plant foliage.
Effects of HCl on tissues are generally restricted to those
immediately affected and are essentially acidic effects. The rapid
solubility of HCl in aqueous media releases hydronium ions, which can
be corrosive to tissue when above a threshold concentration. The
chloride ions may be concentrated in some plant tissues, but may be
distributed throughout the organism, as most organisms have chloride
ions in their fluids. Leaves or other tissues exposed to HCl may show
some concentration above that of their immediate environment; that is,
some degree of bioconcentration can occur. However, long-term storage
in specific organs and biomagnification of concentrations of HCl in
trophic levels of a food chain would not be expected. Thus, the
chemical nature of HCl results in deleterious effects, that when
present, are local rather than widespread.
In conclusion, acute and chronic exposures to expected HCl and
chlorine concentrations around the source are not expected to result in
adverse toxicity effects. These pollutants are not persistent in the
environment. Effects of HCl and chlorine on ponds and soils are likely
to be local rather than widespread. Finally, chlorine and HCl are not
believed to result in biomagnification or bioaccumulation in the
environment. Therefore, we do not anticipate any adverse ecological
effects from chlorine and HCl.
4. Summary of Basis for Proposed Action
The results of the exposure assessment showed exposure levels to
chlorine and HCl emissions from chlorine production facilities are well
below the health threshold values. Furthermore, the threshold values,
for which the RfC and AEGL values were determined to be appropriate
values, were not exceeded when taking into account an ample margin of
safety. Finally, no significant or widespread adverse environmental
effects from chlorine and HCl are anticipated. Therefore, under
authority of section 112(d)(4), we have determined that further control
of chlorine and HCl emissions from chlorine production facilities is
not necessary.
IV. Solicitation of Comments and Public Participation
We seek full public participation in arriving at final decisions
and encourage comments on all aspects of this notice of proposed action
from all interested parties. You need to submit appropriate supporting
data and analyses with your comments to allow us to make the best use
of them. Be sure to direct your comments to the Air and Radiation
Docket and Information Center, Docket No. A-2002-09 (see ADDRESSES).
Dated: June 5, 2002.
Christine Todd Whitman,
Administrator.
[FR Doc. 02-15874 Filed 7-2-02; 8:45 am]
BILLING CODE 6560-50-P