[Federal Register Volume 67, Number 128 (Wednesday, July 3, 2002)]
[Proposed Rules]
[Pages 44713-44719]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-15874]


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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: 
[email protected].

SUPPLEMENTARY INFORMATION: Comments. Comments and data may be submitted 
by electronic mail (e-mail) to: [email protected]. 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

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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.

[[Page 44718]]

    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