A-2002-09
V-C-01
vvEPA
United Sb*«
NATIONAL EMISSION STANDARDS FOR
HAZARDOUS AIR POLLUTANTS
(NESHAP) FOR THE CHLORINE
PRODUCTION INDUSTRY:
Summary of Public Comments and Responses
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EPA-453/R-03-011
August 2003
National Standards for Hazardous Air Pollutants (NESHAP)
for the Chlorine Production Industry:
Summary of Public Comments and Responses
By:
EC/R Incorporated
Durham, North Carolina
Prepared for:
Iliam Rosario
Emission Standards Division
Contract No. 68-D-01-055
Work Assignment No. 1-04
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Emission Standards Division
Metals Group
Research Triangle Park, North Carolina
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Disclaimer
This report is issued by the Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency. Mention of trade names and/or commercial products is not
intended to constitute endorsement or recommendation for use. Copies of this report are
available free of charge to Federal employees, current contractors and grantees, and nonprofit
organizations-as supplies permit-from the Library Services Office (C267-01), U.S.
Environmental Protection Agency, Research Triangle Park, NC 27711, (919-541-2777) or, for a
nominal fee, from the National Technical Information Service, 5285 Port Royal Road,
Springfield, Virginia 22161, (703-487-4650).
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ENVIRONMENTAL PROTECTION AGENCY
National Emission Standards for Hazardous Air Pollutants for the Chlorine Production Industry -
Background Information for Final Action
Prepared by:
Steve Fmh (Date)
Group Leader, Metals Group
Emission Standards Division
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
1. This final decision will delete the non-mercury cell chlorine production subcategory.
2. Copies of this document have been sent to the following Federal Departments: Labor,
Health and Human Services, Defense, Transportation, Agriculture, Commerce, Interior,
and Energy; the National Science Foundation; and the Council on Environmental Quality;
members of the State and Territorial Air Pollution Program administrators; the
Association of Local Air Pollution Control Officials; EPA Regional Administrators; and
other interested parties.
3. For additional information contact:
Mr. IliamRosario
Metals Group (C439-02)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Telephone: (919)541-5308
4. Paper copies of this document may be obtained from:
National Technical Information Services (NTIS)
5285 Port Royal Road
Springfield, VA 22161
Telephone: (703)487-4650
vu
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U.S. EPA Library Services Office (C267-01)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
5. Electronic copies of this document may be obtained from the EPA's OAR Technology
Transfer Network website (TTNWeb).
The TTNWeb is a collection of related Web sites containing information about many
areas of air pollution science, technology, regulation, measurement, and prevention. The
TTNWeb is directly accessible from the Internet via the World Wide Web at the
following address:
http://www.epa.gov/rtn
via
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TABLE OF CONTENTS
1.0 BACKGROUND 1
2.0 SUMMARY OF PUBLIC COMMENTS 3
2.1 EPA'S STATUTORY AUTHORITY 3
2.2 DIRECT SYNTHESIS HCL PRODUCTION UNITS 10
2.2.1 EPA Should Clarify Applicability to Subpart NNNNN 10
2.2.2 EPA Should Reevaluate the MACT Floor for Subpart NNNNN U
2.2.3 EPA Should Apply the Risk Methodology the Subpart NNNNN 12
2.3 HEALTH THRESHOLDS 11
2.3.1 Assumption That Chronic Exposure to Chlorine Will Not Occur 14
2.3.2 Use of AEGL for Short-term Exposure Limits 16
2.4 RISK ASSESSMENT METHODOLOGY 20
2.4.1 General Comments 20
2.4.2 Receptor Locations 22
2.4.3 EPA Has Underestimated Emissions 23
2.4.4 Scope of the Risk Assessment 26
2.4.5 Ecological Assessment 27
2.5 OTHER COMMENTS 30
LIST OF TABLES
TABLE 1. LIST OF COMMENTERS ON PROPOSED DECISION NOT TO REGULATE .. 2
TABLE 2. MAXIMUM HAZARD INDICES 17
TABLE 3. SHORT-TERM MODELING RESULTS 21
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1.0 BACKGROUND
On July 3,2002, the U.S. Environmental Protection Agency (EPA) proposed their
decision not to regulate chlorine and hydrochloric acid emissions from chlorine production
(67 FR 44713) under the authority of section 112(d)(4) of the Clean Air Act (CAA). Public
comments were requested on the proposed decision in the Federal Register. Eight letters were
received from industry representatives, governmental entities, and environmental groups during
the public comment period. A list of the commenters, their affiliations, and the EPA docket
number assigned to their correspondence is presented in Table 1.
The written comments that were submitted, along with responses to these comments, are
summarized in section 2..0 of this document. The summary of comments and responses serves
as the basis for the final decision not to regulate chlorine and hydrochloric acid emissions from
the chlorine production source category.
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TABLE 1. LIST OF COMMENTERS ON PROPOSED DECISION NOT TO REGULATE
DocketNurober Commenter and Affiliation
IV-D-01 Mr. Stephen V. Capone
Manager, Air Regulatory Programs, Environmental, Health & Safety
General Electric Company
One Plastics Avenue
Pittsfield, MA 01201
IV-D-02 Mr. Gabriel Calvo
Hunton and Williams
Counsel for Utility Air Regulatory Group
1900 K Street, NW
Washington, DC 30006-1109
IV-D-03 Mr. Kevin P. Batt, P.E.
EH&S Regulatory Management Expertise Center
The Dow Chemical Company
437 MacCorkle Avenue, S.W.
South Charleston, WV 25303
IV-D-04 Mr. Robert G. Smerko
President
The Chlorine Institute, Inc.
2001 L Street, N.W.
Washington, DC 20036-4919
IV-D-05 Mr. T. Ted Cromwell
Senior Director, Air Team
American Chemistry Council
1300 Wilson Boulevard
Arlington, VA 22209
IV-D-06 Mr. Thomas Gentile
Chief, Toxics Assessment Section, Bureau of Stationary Sources, Division of
Air Resources
New York State Department of Environmental Conservation
625 Broadway
Albany, NY 12233-3254
IV-D-07 Mr. James Pew
Earthjustice
IV-D-08 Mr. John Walke
Director, Clean Air Program
Natural Resources Defense Council
1200 New York Avenue, NW, Suite 400
Washington. DC 20005-3928
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2.0 SUMMARY OF PUBLIC COMMENTS
A total of eight written comments were received on the proposed action. The following
sections provide a summary of these comments, as well as the Agency's responses. For the
purpose of orderly presentation, the comments have been categorized under the following topics:
EPA'S Statutory Authority
• Direct Synthesis HC1 Production Units
Health Thresholds
• Risk Assessment Methodology
• Other Comments
2.1 EPA'S STATUTORY AUTHORITY
Comment: Several comments were received related to EPA's decision not to regulate
chlorine and HC1 emissions from chlorine production under the authority of section 112(d)(4).
Some commenters supported this decision and believed EPA's interpretation of their authority
under section 112(d)(4) was appropriate and supported by the legislative history. In contrast,
other commenters disagreed with EPA's interpretation of section 112(d)(4). Finally, some of the
commenters believed that the delisting of the non-mercury cell chlorine production subcategory
under the authority of section 112(c)(9)(B)(ii) was warranted.
EPA's decision is appropriate under section 112(d)(4). Five commenters (TV-D-01, IV-
D-02, F/-D-03, IV-D-04, FV-D-05) supported EPA's decision not to regulate chlorine and HC1
emissions from non-mercury cell chlorine production plants under the authority of section
112(d)(4). One commenter (TV-D-01) stated that EPA conducted an appropriate analysis to
determine that human exposures from ambient concentrations are well below threshold values
with an ample margin of safety. According to another commenter (TV-D-04), any further
regulation of chlorine and HC1 emissions from the chlorine production industry would have no
environmental benefits, but would result in costs for monitoring, recordkeeping, and reporting
efforts to certify compliance with any requirements. The commenter (TV-D-04) was concerned
that a regulation would also stretch EPA's limited resources in monitoring for compliance.
Three commenters (TV-D-02, IV-D-03, IV-D-05) stated that EPA's interpretation of their
authority under section 112(d)(4) was supported by the legislative history, which emphasizes that
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Congress included section 112(d)(4) in the CAA to prevent unnecessary regulation of source
categories. To support this position, one commenter (IV-D-02) referred to the following portion
of a Senate report:
[WJhere some sources do emit more than the threshold amount, the Administrator
is authorized by section 112(d)(4) to use the no observable effects level or NOEL
(again with an ample margin of safety) as the emission limitation in lieu of more
stringent "best technology" requirements. Following this scenario, only those
sources in the category which present a risk to public health (those emitting in
amounts greater than the safety threshold) would be required to install controls,
even though the general policy is "maximum achievable technology everywhere."
Again, there is a means to avoid regulatory costs which would be without public
health benefit.
[Sen. Rep. 101-228, at 176(1989), reprinted in 1990 U.S.C.C.A.N. 3385,3561.]
The commenter agreed that under section 112(d)(4), once EPA establishes that a pollutant has a
health threshold and that exposure to that pollutant's emissions are below the health threshold,
EPA should refrain from setting MACT standards for that pollutant. The commenter further
suggested that EPA should use section 112(d)(4) whenever setting emission standards under
section 112(d).
EPA's decision is not supported by section 112(d)(4). Three commenters (FV-D-06, IV-
D-07, FV-D-08) disagreed with EPA's interpretation of section 112(d)(4). They did not believe
that section 112(d)(4) could be used as an alternative to setting MACT standards under section
112(d)(3). One commenter (TV-D-06) noted that the phrase "in lieu of was not included in the
section 112(d)(4) provisions and that its absence was intentional. In support of their claim, the
commenter pointed to section 112(d)(5), which does contain the phrase "in lieu of." The
commenter (TV-D-06) interpreted section 112(d)(4) to mean that health based thresholds can be
considered when establishing the degree of MACT requirements, but not hi place of the
requirement to establish a MACT floor pursuant to section 112(d)(3).
The commenter (IV-D-06) also pointed to the provisions of section 112(c)(2) which
require the Administrator to establish NESHAP for listed source categories and subcategories.
The commenter was concerned that EPA evaluated emissions from chlorine production plants
and concluded that since they do not pose a threat to human health and the environment, the
Administrator is relieved of her responsibilities to establish a MACT standard. The commenter
maintained that this position is not supported by section 112(c)(2).
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The commenter also referred to section 1 12(d)(l) which states ". . . the Administrator
shall promulgate regulations establishing emission standards for each category or subcategory of
major sources and area sources of hazardous air pollutants listed for regulation pursuant to
subsection (c) of this section — " Thus the commenter stated that EPA did not have the
authority to "make a determination of no regulation for a listed source category or pollutant."
Finally, the commenter referred to section 1 12(d)(3), which contains the MACT floor
provisions. According to the commenter, the intent of the NESHAP program is to develop a
MACT floor, and EPA is not fulfilling the requirements of the CAA by not performing such an
analysis. The commenter stated that a majority of facilities identified in the analysis have
adequate controls due to State regulations and these controls should be incorporated into the
MACT floor evaluation. The commenter was particularly concerned that by not developing a
MACT floor, no new-source MACT standards was created. The commenter requested EPA
perform a MACT floor analysis and develop a NESHAP for new sources.
EPA should delist the source category under section 112(c)(9)(B)(ii). Two of the
commenters (TV-D-03, IY-D-05) that supported the action under 1 12(d)(4) indicated that section
1 12(d)(4) seems to be designed for the setting of standards, rather than a decision to not regulate
a source category. They stated that EPA should support then- decision not to regulate the chlorine
production source category by citing the provisions of section 1 12(c)(9)(B)(ii) in addition to the
provisions of section 1 12(d)(4). The commenters stated that the evaluation performed by EPA
would also be sufficient for deleting sources under section 1 12(c)(9)(B)(ii) and that EPA's
proposal to not regulate chlorine production is similar to deleting a subcategory of the Chlorine
Production source category (i.e., all chlorine production sources other than those using the
mercury-cell chlor-alkali production process). Therefore, in addition to using the authority under
section 1 12(d)(4), the commenters suggested that EPA delete the subcategory using the authority
under section 1 12(c)(9)(B)(ii) to avoid any uncertainty over the use of its authority under section
Response: The chlorine production source category was initially listed as a category of
major sources of HAP pursuant to section 1 12(c)(l) of the CAA on July 16, 1992 (57 FR 31576).
Our analysis shows that the only HAP emitted from sources within this chlorine production
source category are chlorine, HC1, and mercury, and mercury is only emitted from mercury cell
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chlor-alkali plants. ^Because of the differences in the production methods and the HAP emitted,
we decided to divide the chlorine production category into two subcategories: (1) mercury cell
chlor-alkali plants, and (2) chlorine production plants that do not rely upon mercury cells for
chlorine production (diaphragm cell chlor-alkali plants, membrane cell chlor-alkali plants, etc).
Thus, on July 3,2002, we issued separate proposals to address the emissions of mercury from the
mercury cell chlorine production subcategory sources (67 FR 44672) and the emissions of
chlorine and HC1 from both the non-mercury cell chlorine production subcategory and the
mercury cell chlorine production subcategory sources (67 FR 44713). While we are finalizing
the NESHAP for the mercury cell chlor-alkali subcategory, with certain modifications from the
proposal (including our decision not to regulate chlorine and HC1 emissions under the authority
of CAA section 112(d)(4)), we have decided to delete the non-mercury cell chlorine production
subcategory in accordance with CAA section 112(c)(9)(B)(ii).
Section 112(c)(9)(B)(ii) states the following:
(B) The Administrator may delete any source category...
(ii) In the case of hazardous air pollutants that may result in adverse health effects
in humans other than cancer or adverse environmental effects, a determination
that emissions from no source in the category or subcategory concerned (or group
of sources in the case of area sources) exceed a level which is adequate to protect
public health with an ample margin of safety and no adverse environmental effect
will result from emissions from any source (or group of sources hi the case of area
sources."
We agree with those two commenters who suggested that exercising our authority under
CAA section 112(c)(9)(B)(ii) is appropriate for this subcategory for a number of reasons. First,
CAA section 112(c)(9)(B)(ii) permits the deletion of subcategories, and that is what is at issue
here. We are not deleting the entire chlorine production category; neither are we deleting the
mercury cell subcategory, the emissions from which and production methodology are different
from those facilities that produce chlorine using diaphragm cells, membrane cells, and the
various processes that produce chlorine as a by-product. Second, the only HAPs emitted in
significant quantities from the facilities in this subcategory are chlorine and HC1. Chlorine and
HC1 are not carcinogens (http://www.epa.gov/irisA). Third, as indicated in the proposal, both of
these HAPs are threshold pollutants (see next comment and response). For the proposed action,
we obtained chlorine and HC1 emission estimates from every known major source facility in the
non-mercury cell chlorine production subcategory using our authority under section 114 of the
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CAA and conducted risk assessments for each facility. We then updated these assessments based
on comments received (see section 2.4). Our analysis showed both at the time of proposal and
shows now that emissions of these HAP from every source in the non- mercury cell chlorine
production subcategory do not exceed a level which is "adequate to protect public health with an
ample margin of safety." Finally, our evaluation of environmental effects indicates that no
adverse impacts will result from emissions from any source within the subcategory. Therefore,
we agree with the commenters that our evaluation is sufficient for deleting the subcategory under
CAA section 112(c)(9)(B)(ii), and that such action is justified as a logical outgrowth of public
comments received on our proposed action.
We have reviewed in some detail the comments of those which have questioned our
proposed use of CAA section 112(d)(4) to not establish a NESHAP for chlorine and HC1
emissions from facilities within the non-mercury cell chlorine production subcategory. We do
not agree with these comments, and we are exercising our authority under CAA section 112(d)(4)
to not regulate chlorine and HC1 emissions from the mercury cell chlorine production source
category. We have decided to delete the non-mercury cell subcategory under CAA section
112(c)(9)(B)(ii) for the reasons stated above. We do not feel that we are obligated to exercise
our authority under both CAA 112(d)(4) and CAA section 112(c)(9)(B)(ii) as suggested by the
commenter. Therefore, our decision is to delete the non-mercury cell chlorine production
subcategory under CAA section 112(C)(9)(B)(ii). The NESHAP mercury cell chlorine
production subcategory is being promulgated in a separate action.
Comment: One commenter (TV-D-08) submitted comments that it had provided to EPA
on the proposed NESHAP for Brick and Structural Clay Products Manufacturing category. Most
of these comments pertained to a different set of circumstances on a proposed use of section
112(d)(4) (source specific exemptions) that are not applicable to the chlorine production
category. However, the commenter did maintain that the plain language of the CAA requires
EPA to set emission standards for listed source categories and that section 112(d)(4) could only
be used for pollutants with a well-established health threshold. Along this line, another
commenter (TV-D-07) indicated that the EPA did not sufficiently establish health thresholds for
HC1 and chlorine. First, the commenter disagreed with EPA's use of the Reference
Concentration (RfC) for HC1 of 20 micrograms per cubic meter based on the proposed standards
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for chemical recovery combustion sources at pulp and mills (63 FR 18753). The commenter
argued that the pulp and paper action was only a proposal and no final determination was made.
Furthermore, the commenter argued that EPA's Group D determination for HC1 was for the
purposes of the pulp and paper action only (63 FR 18766). Therefore, the commenter concluded
that the pulp and paper action does not set a cancer threshold for HC1 for other source categories.
The commenter also stated that a Group D classification does not constitute a health threshold; it
is an admission that EPA does not know whether a pollutant is a carcinogen. The commenter
concluded that EPA did not establish either cancer or non-cancer thresholds for HC1 and
therefore, it is illegal for EPA to attempt to use section 112(d)(4) to set standards.
The commenter (IV-D-Q7) also did not agree with EPA's rationale for determining that
chlorine is a threshold pollutant. The commenter did not believe it was appropriate for EPA to
"presumptively consider" chlorine as a threshold pollutant based on its knowledge of how
chlorine reacts in the body, its likely mechanism of action, and the limited negative
carcinogenicity data. The commenter argued that EPA has not shown that there are established
cancer and non-cancer thresholds for chlorine and it is unlawful for EPA to use section 112(d)(4)
to set standards for chlorine.
Further, this commenter stated that the legislative history shows that Congress intended
for EPA to use section 112(d)(4) only for those pollutants with no adverse health effects,
including short term health effects. According to the commenter, EPA has not proven that there
are no short term adverse health effects due to chlorine and HC1 emissions. The commenter
referred to EPA's statement in the proposed action that EPA was beginning to develop short term
exposure values (67 FR 44716). Therefore, the commenter stated that if EPA was beginning to
develop short term exposure values, it was not possible for EPA to have established short term
exposure threshold values. The commenter contended that it was illegal for EPA to decide to use
short term threshold values even though short term threshold had not been independently
established.
Response: Section 112(d)(4) states that, "With respect to pollutants for which a health
threshold has been established, the Administrator may consider such threshold level, with an
ample margin of safety, when establishing emission standards under this subsection." The
threshold level refers to the level of concentration of a chemical under which no health effects are
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expected from exposure, although this term is not defined in CAA section 112. Further, CAA
section 112 does not address the process that must be followed to "establish" a threshold level.
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 HC1 of 20 micrograms per cubic meter (ng/m3) is
an appropriate threshold value for assessing risk to. humans associated with exposure to HC1
through inhalation (http://www.epa.gov/iris/subst/0396.htm').
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 ^g/m3 for chlorine
based on a large inhalation study with rats.
Acute exposure guideline level (AEGL) toxicity values are estimates of adverse health
effects due to a single exposure lasting eight 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 EPA has developed AEGL's 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 AEGL values (65 FR 39264, June 23, 2000), including the 1-hour, AEGL1 of
2,700 ng/m3 used in our revised analysis. Chlorine has also been assigned AEGL values (62 FR
58840), including the 1 hour AEGL1 of 1,500 fig/m3 used in our revised analysis.
We maintain that the listing of health thresholds by EPA and other organizations in the
public domain as discussed above has established health thresholds for HC1 and chlorine.
Further, we believe that the recognition of these levels by EPA, ASTDR, and CAL EPA indicates
that chlorine and HC1 are threshold pollutants.
Moreover, we provided the public an opportunity to comment on the thresholds for
chlorine and HC1 that we used in our original analysis for the proposed action. We used the same
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threshold level for HCl for both the proposed and final NESHAP for the pulp and paper mill
category. (Although there is no mention of the HCl threshold in the final rule preamble for the
pulp and paper mill NESHAP, we received no comment on the use of the threshold and used it in
deciding not to set a limitation for HCl in the final NESHAP). We have also used the same
threshold for HCl in the proposed NESHAP for lime production (67 FR 78046). There is no
requirement in either CAA section 112(d)(4) or CAA section 112(c)(9)(B)(ii) that EPA develop
or finalize a threshold for a particular HAP in a certain manner. In fact, CAA section
112(c)(9)(B)(ii), the authority we are utilizing here, does not mention the term threshold
(although the term is implied by the use of the phrase "a level which is adequate to protect public
health with an ample margin of safety"). The thresholds we have used for both HCl and chlorine
are consistent with the statutory language in CAA section 112(c)(9)(B)(ii).
2.2 DIRECT SYNTHESIS HCL PRODUCTION UNITS
2.2.1 EPA Should Clarify Applicability to Subpart NNNNN
Comment: Four commenters (TV-D-01, FV-D-03, IV-D-04, IV-D-05) supported EPA's
decision to include direct synthesis HCl as a part of the non-mercury cell chlorine production
process. According to one commenter (IV-D-01), since EPA's risk analyses incorporated
emissions from both chlorine and direct synthesis HCl production at chlor-alkali facilities, it is
appropriate to conclude that they are part of the same process. However, the commenter (IV-D-
01) requested that we clarify that chlorine and HCl emissions from the absorber vents and
associated storage vessels and transfer racks of the direct synthesis HCl production units were
included in the risk analyses, and therefore, EPA has decided it is not necessary to regulate
emissions from these sources. To clarify applicability to the HCl Production NESHAP (40 CFR
part 63, subpart NNNNN), commenter IV-D-04 suggested that EPA modify the applicability
provisions [§63.8985(e)J of subpart NNNNN as follows:
(e) You are not subject to this subpart if you operate a direct synthesis HCl
production unit at a chlor-alkali facility.
Two commenters (IV-D-03, IV-D-05) also requested that EPA reevaluate collocated
chlorine and HCl production sources and provide guidance so that the facilities can easily
determine to which source category they belong. According to the commenters, collocated
chlorine and HCl production sources may share transfer operations and storage tanks, and where
appropriate, EPA should remove all facilities from the HCl acid production source category that
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meet the logical test outlined in the proposed action. The commenters stated that they believe the
collocated integrated chlorine and HC1 acid production facilities should be placed in the non-
mercury cell chlorine production source category and removed from the HC1 acid production
source category.
Response: In the final rule for subpart NNNNN (68 FR 19076, April 17,2003), states,
§63.8985(d), that an "HC1 production facility is not subject to this subpart if it produces HC1
through the direct synthesis of hydrogen and chlorine and is part of a chlor-alkali facility." The
definition of "HC1 production facility" in subpart NNNNN includes "all HC1 storage tanks that
contain liquid HC1 product that is produced in the HC1 production unit" (e.g., direct synthesis
unit) as well as "all HC1 transfer operations that load HC1 product produced in the HC1
production unit into a tank truck, rail car, ship, or barge, along with the piping and other
equipment in HC1 service used to transfer liquid HC1 product from the HC1 production unit to the
HC1 storage tanks and/or HC1 transfer operations." Therefore, we have clarified that chlorine and
HC1 emissions from the absorber vents of direct synthesis HC1 production units at chlor-alkali
facilities, as well as the associated storage tanks and transfer operations specified above, are
included in the non-mercury cell chlorine production source category and are not regulated under
subpart NNNNN.
The clarifications we made in subpart NNNNN provide guidance for sources to determine
to which source category their operations belong. As stated above, all HC1 production facilities
at chlor-alkali plants that produce HC1 through direct synthesis are part of the non-mercury cell
chlorine production subcategory. All other HC1 production facilities (e.g., those that produce
HC1 as a co-product of a chlorinated organic compound) at sites where chlor-alkali plants are
located are part of the HC1 Production source category and subject to subpart NNNNN. In the
case of shared storage tanks and transfer operations, any storage tank that stores, and any transfer
operation that loads, liquid HC1 product which was produced in an HC1 production facility that is
subject to subpart NNNNN is subject to the provisions of that subpart.
2.2.2 EPA Should Reevaluate the MACT Floor for Subpart NNNNN
Comment: Three commenters (TV-D-01, IV-D-03, IV-D-05) requested that EPA
reevaluate the HC1 production source category MACT floor to remove any direct HC1 synthesis
facilities that were included as part of the Chlorine production source category. One commenter
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(TV-D-01) stated that they had submitted section 114ICR responses for their two direct synthesis
HC1 production units under the HC1 production NESHAP (subpart NNNNN). The commenter
(IV-D-01) stressed that it is important to remove these units from each database used to establish
a floor for the HC1 production source category. The commenter (IV-D-01) was concerned that
these four units' low emissions would inappropriately influence the calculation of the floor for
the HC1 production source category.
Two commenters (TV-D-03, IV-D-05) identified at least six facilities that may include
either direct synthesis HC1 and/or collocated chlor-alkali and HC1 acid production facilities that
have been identified in both the Chlorine Production and Hydrochloric Acid source categories.
The commenters (IV-D-03, IV-D-05) pointed out that both categories are regulated for emissions
of only HC1 and chlorine. The commenters (IV-D-03, IV-D-05) suggested that the source
categories were analogous and that risk determinations apply to one source category.
Response: The MACT floor data set that we used to determine the final MACT for HC1
Production (subpart NNNNN) does not contain any HC1 production facilities that were identified
as being direct synthesis units that are part of chlor-alkali plants. Therefore, the two facilities
specifically mentioned by commenter IV-D-01 were not used in the determination of MACT for
HC1 Production.. Of the six plants specifically mentioned by commenter IV-D-05, three were not
included in the final MACT floor data set. The other three plants were included because we had
data for HC1 production facilities at these plant sites that produce HC1 by means other than direct
synthesis. As we explained above, such HC1 production facilities are still subject to subpart
NNNNN. The direct synthesis units at these three plants were not included hi the MACT floor
for HC1 Production.
2.2.3 EPA Should Apply the Risk Methodology the Suboart NNNNN
Comment: Two commenters (IV-D-03, IV-D-05) stated that many of the HC1 acid
production facilities that are subject to the HC1 production MACT (subpart NNNNN) exhibit the
same chlorine and HC1 emissions profiles as those identified in the chlorine production source
category. The commenters (IV-D-03, IV-D-05) analyzed the chlorine and HC1 emissions
reported in the docket for both chlorine production and HC1 acid production source categories
and determined that seven of the HC1 acid production source category facilities did not emit more
than the worst-case chlorine production facility and six facilities emitted between one time and
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five times the worst case chlorine production facility (chlorine emissions were converted to HC1
emissions to remain consistent with EPA's analysis for the risk assessment). The commenters
(FV-D-03, FV-D-05) indicated that they were gathering data from other facilities in the HC1 acid
production source category and that preliminary data suggests that several additional facilities
emit HC1 and chlorine in quantities not exceeding amounts EPA has determined would exceed
the RfC and/or AEGL2 concentrations. Therefore the commenters (TV-D-03, IV-D-05) stated
that they believe that it could be shown that these HC1 acid production facilities do not represent
significant emission risks using a risk assessment process similar to that used in the proposed
action. The comrnenters (IV-D-03, IV-D-05) recommended that specific actions related to any
HC1 acid production risk assessment proceed after the chlorine production action is finalized.
Response: We acknowledge that there are similarities between the HC1 Production and
Chlorine Production source categories in terms of the HAP emitted (and available controls), and
concur with the comparisons of emission levels. However, these are separately listed source
categories under section 112(c)(l) of the Act, any action taken for the HC1 Production Source
Category will be separate and distinct from this action on the Chlorine Production Source
Category.
2.3 HEALTH THRESHOLDS
Comment: Three commenters (TV-D-02, IV-D-03, IV-D-05) supported EPA's
characterization of RfC and AEGL values and encouraged EPA to recognize the uncertainty and
variability inherent in these values in future risk assessments. According to the commenters, the
RfC and AEGL contain sufficiently conservative assumptions such that modeled exposure
concentrations equal to the RfC or AEGL would provide an ample margin of safety.
The commenters (IV-D-02, IV-D-03, IV-D-05) agreed with EPA's determination that the
inherent uncertainty factors contained within the RfC and AEGL2 values used in the risk
assessment result in a more conservative overestimation of the noncancer effects. In fact, the
commenters stated that these uncertainty factors are key to the ample margin of safety
determination. However, the commenters stated that they believe the uncertainty factors required
to demonstrate an ample margin of safety are captured within the associated health thresholds for
chlorine and HC1. The commenters recommended that EPA determine a safe threshold and
ample margin of safety threshold based solely on the underlying health values and the uncertainty
13
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associated with these values. According to the commenters, RfCs and AEGLs are established
with these considerations in mind and should be deemed adequate in establishing which exposure
concentrations constitute an ample margin of safety. Under this procedure, the commenters
stated that modeled exposure concentrations would be compared to the ample margin of safety
level, greater than or equal to the RfC or AEGL, to determine whether an ample margin of safety
had been achieved. Therefore, the commenters concluded that a hazard quotient greater than or
equal to one would be acceptable and would be consistent with EPA's risk assessment.
Response: As discussed in previous comments, we agree with the commenters regarding
the appropriateness of using RfC and AEGL values for this assessment. We do recognize the
inherent uncertainty and variability inherent in these values. A hazard index of less than 1 is
generally considered to be "safe." However, we also believe that when considering the
noncancer impact of a single source, levels less than 1 may not be acceptable. This is because
other sources of exposure (e.g., indoor sources, mobile sources, natural background, etc.) are not
being accounted for in a single-source analysis. This means that individuals could be exposed to
concentrations in excess of the dose-response value (i.e., hazard indices greater than 1).
Therefore, we do not necessarily agree with the comments that a hazard quotient of 1 is always
an appropriate threshold that should be considered acceptable.
2.3.1 Assumption That Chronic Exposure to Chlorine Will Not Occur
Comment: Two commenters (TV-D-03, IV-D-05) supported EPA's use of the HCl RfC to
determine the long-term health effects of chlorine emissions. The commenters (IV-D-03, IV-D-
05) stated that EPA's decision was based on sound scientific knowledge of the pollutants of
concern.
In contrast, two commenters (TV-D-06, IV-D-07) did not agree with EPA's use of the HCl
RfC as a threshold level for chlorine. The commenters stated that not all of the annual chlorine
emissions can be considered as HCl and, therefore, the chlorine exposure was underestimated.
The commenters argued that chlorine emissions will not undergo photolysis to convert to HCl
when there is not bright sunshine (i.e., at night or on cloudy days). One commenter (IV-D-06)
requested that EPA adjust the background equations to properly reflect the atmospheric
chemistry. The commenter (IV-D-06) further stated that the use of atmospheric chemistry is
traditionally conducted under a more refined risk assessment process. Therefore, the commenter
14
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concluded that it is not appropriate for EPA to undertake a refined risk analysis at this time, until
the provisions of section 112(f) (i.e., the residual risk provisions) have been established for doing
consistent screen level and more refined residual risk analysis.
Response: The widely accepted fact that chlorine is photolyzed in sunlight formed the
basis for the assumption in the original risk assessment that chronic exposure to chlorine would
not occur. As a result of this comment, we re-examined the literature on the atmospheric fate of
chlorine in the atmosphere to validate our original assumption.1
The additional information obtained from the literature confirmed our earlier information.
There are several different pathways that molecular chlorine can take, including photolysis
(reaction with light), reactions with hydroxyl radicals (OH), reactions with oxygen atoms (0),
and reactions with water vapor (H2O). Each pathway results in different amounts of chlorine
being removed from the troposphere, and different pathways are predominant at different times
of the day. However, photolysis is the primary pathway.
Therefore, this information did not fundamentally change the assumption made in the
original risk assessment, which was that on a long-term basis, individuals will be exposed more
to hydrochloric acid formed from the photolysis of chlorine than to chlorine. However, the
commenters are correct that there will be situations where individuals will be exposed to
chlorine. Therefore, in addition to the assessment where we considered only acute exposure to
chlorine, we concluded that it was appropriate to consider the effects of chronic exposure to
chlorine emissions from chlor-alkali plants.
One commenter suggested that the background equations could be adjusted to properly
reflect the atmospheric chemistry. This was not done for the re-assessment. Rather, modeling
was conducted assuming that no chlorine is photolyzed.2 This provided an upper bound estimate
of the chronic risks to compare with the lower bound estimates assuming that all chlorine was
converted to HC1. Table 2 shows the results of this upper bound assessment assuming no
1 Memorandum. Norwood, P. and Smith, D., EC/R Incorporated, Chapel Hill, North
Carolina, to Rosario, I., EPA/OAQPS/ESD/MG. Revised Risk Assessment for Chlorine
Production Facilities. July 18, 2003.
2 Reference 1.
15
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chlorine is converted to HC1, along with the results of the original assessment which assumed all
chlorine is converted to HC1.
In general, we consider an exposure concentration which is below the RfC concentration
(what we call a hazard quotient less than 1) to be safe. This is based on the definition of RfC.
The RfC is a peer reviewed value defined as an estimate (with uncertainty spanning perhaps an
order of magnitude) of a daily inhalation exposure to the human population (including sensitive
subgroups) that is likely to be without appreciable risk of deleterious noncancer effects during a
life time (i.e., 70 years).
We conducted additional modeling for all facilities within the subcategory using the same
model used for the proposed action (ISCST3) to estimate chronic chlorine exposure using the
assumption that no chlorine is photolyzed to HC1.3 The hazard quotients resulting from this
additional modeling defined the upper bound of our risk assessment. As can be seen in Table 2,
the highest upper-bound hazard quotient estimated by the model is just over 0.3 and the highest
lower bound hazard index is 0.03. Given the health protective assumptions used in this analysis,
the value of 0.3 represents a hypothetical exposure that is well above what we would expect
actual exposures to be. This is because chlorine is converted to HC1 in the presence of sunlight
within a few minutes. In addition, the hazard quotient of 0.3, which results from this exposure
scenario is well below the safe value of 1. Thus, we have concluded that, even assuming that
some chronic exposure to chlorine may occur, none of the sources included in this subcategory
will have emissions of chlorine or HC1 that exceed a level of exposure which is adequate to
protect public health and the environment with an ample margin of safety.
2.3.2 Use of AEGL for Short-term Exposure Limits
Comment: Two commenters (TV-D-06, FV-D-07) did not support EPA's use of the
AEGL2 for use as a short-term exposure limit for chlorine and HC1. One commenter (FV-D-07)
stated that the AEGL2 values would not sufficiently protect public health because they would
allow emissions at levels that cause discomfort, and according to the commenter, discomfort is
an adverse health effect. The commenter also complained that EPA did not explain why it chose
to use AEGL2 rather than AEGL1 or AEGL3. The commenter explained that although
3 Reference 1.
16
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TABLE 2. MAXIMUM HAZARD INDICES
Facility ID
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
Facility Name
Occidental Chemical Corporation
Occidental Chemical Corporation
Oxy Vinyls, LP
Oxy Vinyls, LP
Georgia Gulf Chemicals/Vinyls
Bayer
Vulcan Chemicals
GE Plastics Mt. Vernon, Inc.
General Electric Company
Vulcan Chemicals
Dow Chemical Company
Dow Chemical Company
Georgia Pacific
Georgia Pacific
Georgia Pacific
PPG Industries, Inc
PPG Industries, Inc
Formosa Plastics Corp.
Formosa Plastics Corp.
Occidental Chemical Corporation
Location
Ingleside, TX
Convent, LA
Battleground, TX
Deer Park, TX
Plaquemine, LA
Baytown, TX
Wichita, KS
Mt. Vernon, IN
Burkville, AL
Geismer, LA
Freeport, TX
Plaquemine, LA
Muskogee, OK
Savannah River, GA
Green Bay, WI
Natrium, WV
Lake Charles, LA
Point Comfort, TX
Baton Rouge, LA
Niagara Falls, NY
Maximum Hazard Index
Assuming all
Chlorine is
Converted to
HC1
0.0005
0.002
0.0005
0.001
3.0x10-"
0.004
0.01
0.0003
0.00007
0.00002
0.00005
0.00005
0.004
0.0004
0.0007
0.002
0.02
0.002
0.003
0.03
Assuming no
Chlorine is
Converted to
HC1
0.05
0.10
0.03
0.10
5.2x10"'
0.17
0.17
0.004
0.003
0.002
0.004
0.32
0.21
0.02
0.05
0.04
0.34
0.22
0.16
0.22
17
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emissions from chlorine plants did not exceed AEGL2 values, the emissions may exceed AEGL1
values, and if they did, the proposed action would not meet the statutory requirements.
Therefore, the commenter argued that without an explanation for why they chose the AEGL2
value, the Agency appeared to have made an arbitrary and capricious decision.
One commenter (IV-D-06) stated that AEGL limits are not appropriate for assessing daily
human exposure scenarios because they were developed for emergency planning. The
commenter further argued that EPA misinterpreted the definition of an AEGL2 value in the
proposed action. The commenter referred to a definition for AEGL provided by EPA in 1997:
"AEGL2 is the airborne concentration (expressed as ppm of mg/m3) of a
substance at or above which it is predicted that the general population, including
susceptible, but excluding hypersusceptible individuals, could experience
irreversible or other serious, long-lasting effects or impaired ability to escape.
Airborne concentrations below the AEGL2, but at or above AEGL1 represent
exposure levels that may cause notable discomfort." (62 FR 201)
According to the commenter, the AEGL2 chlorine value was derived from a study in which
healthy human subject experienced transient changes in pulmonary function and a sensitive
individual experienced an asthmatic attack.4 Therefore, both commenters (IV-D-06, IV-D-07)
concluded that the AEGL2 value was not an appropriate guideline for the protection of the
general public and does not provide an ample margin of safety. Commenter IV-D-06 also
mentioned that the AEGL1 value was based on the same study but healthy subjects experienced
no sensitory irritation and transient changes in some pulmonary function were experienced for a
sensitive individual.
The commenter (TV-D-06) recommended that EPA should use the American Conference
of Governmental Industrial Hygienists (ACGIH), which has a one-hour Short Term Exposure
Limit (STEL) similar to the AEGL1 value of 1 parts per million (ppm) (for chlorine) and is used
v
to protect against eye and mucous membrane irritation. The commenter's policy as a State
agency is to add an additional safety factor often to ACGIH STEL values to protect for sensitive
individuals, since ACGIH values were established for healthy workers. The commenter stressed
"Rotman, et. al., Effects of Low Concentrations of Chlorine on Pulmonary Function in
Humans. 1983.
18
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that EPA must use conservative benchmarks before concluding that an ample margin of safety
exists.
Response: The AEGL values represent short-term threshold or ceiling exposure values
intended for the protection of the general public, including susceptible or sensitive individuals,
but not hypersusceptible or hypersensitive individuals. The AEGL values represent biological
reference values for this defined human population and consist of three biological endpoints for
each of four different exposure periods of 30 minutes, 1 hour, 4 hours, and 8 hrs. The commenter
correctly cited the definition of the AEGL2 level. As utilized hi the proposed action, the AEGL2
1-hour concentrations for chlorine and HC1 are 5,800 ug/m3 and 33,000 ug/m3, respectively.
The AEGL-1 level is defined as follows:
AEGL-1 is the airborne concentration of a substance at or above which it is
predicted that the general population, including "susceptible" but excluding
"hypersusceptible" individuals, could experience notable discomfort. Airborne
concentrations below AEGL-1 represent exposure levels that could produce mild
odor, taste, or other sensory irritations.
The 1-hour AEGL-1 concentration for chlorine is 2,900 (ag/m3 and the corresponding
value for HC1 is 2,700 Hg/m3. The ACGIH short term exposure limit (STEL) for chlorine, which
is 1 ppm,5 is approximately equal to the AEGL-1 value of 2,900 ug/m3.
Although we stand by our original analysis, which used the AEGL2 level, we have
referenced the commenter's suggested use of the AEGL1 values (possibly with a safety factor)
for determining whether an ample margin of safety has been obtained. Therefore, we simply
compared the short term (1-hour average) modeling results from the original risk assessment to
the AEGL1 values. These results were obtained by modeling the maximum allowable hourly
emissions reported in the section 114 responses for each of the sources. For plants that did not
report fugitive emissions, fugitive emissions were estimated using worst-case emission factors.
As can be seen in Table 3, the maximum modeled 1-hour chlorine concentration for 16 of
the 20 plants is less than 5 percent of the AEGL1 (and ACGIH) value for chlorine. Further, the
highest modeled concentration for any plant, 346 ug/m3, is less than 12 percent of the AEGL1
5 Chlorine Chemical Backgrounder. National Safety Council Website.
nttp ://www.nsc. org/librarv/chemical/chl orine.htm
19
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values. The highest modeled 1-hour HC1 concentration for any plant, 120 ug/m3, is less than
5 percent of the AEGL1 value for Hcl.
Based on this comparison, we conclude that the chlorine and HC1 emissions from chlor-
alkali plants do not represent an unsafe level of acute exposure. We further maintain, along with
the chlorine exposure assessment, that proves that an ample margin of safety is provided with no
additional control of this industry.
2.4 RISK ASSESSMENT METHODOLOGY
2.4.1 General Comments
Comment: Two commenters (IV-D-03, IV-D-05) supported EPA's method of selecting a
risk assessment approach to meet the unique needs of the chlorine production industry. The
commenters (TV-D-03, IV-D-05) agreed that the risk assessment methodology should not be
interpreted as a standardized approach that would set a precedent for how EPA will apply CAA
section 112(d)(4) in future cases. Furthermore, the commenters (TV-D-03, IV-D-05) stated that
degree of conservatism built into all aspects of the risk assessment conducted for the chlorine
production source category could vary greatly in future risk assessments for other source
categories. The commenters (IV-D-03, IV-D-05) stressed that they believe that the conservative
assumptions made in the health effects assessment, emissions estimates, and exposure
assessment were appropriate for the proposed action.
In contrast, one commenter (FV-D-07) stated that the risk assessment fell short of the
Agency's prior practice. According to the commenter, whenever EPA has made determinations
to regulate a specific pollutant based on health considerations (e.g., national ambient air quality
standards (NAAQS) for ozone and particulate matter (PM)), the Agency evaluated health effects
and exposure in great detail. The commenter contended that in this case, EPA appears to be
content with "the bare and unsupported assumptions about what health levels are safe." The
commenter argued that it was not appropriate for EPA to use a rigorous approach when setting
standards and a more cursory approach when making a decision not to regulate.
Response: We disagree with Commenter IV-D-OT's characterization of the assessment
that forms the basis for this decision, and we strongly dispute the characterization of the
assessment as "bare and unsupported." We maintain that the RfC and AEGL values used as
benchmarks for this assessment are scientifically sound and appropriate. The emissions data and
20
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TABLE 3. SHORT-TERM MODELING RESULTS
Facility
ID
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
Facility Name
Occidental Chemical
Occidental Chemical
Oxy Vinyls, LP
Oxy Vinyls, LP
Georgia Gulf
Bayer
Vulcan Chemicals
GE Plastics
General Electric
Vulcan Chemicals
Dow Chemical
Dow Chemical
Georgia Pacific
Georgia Pacific
Georgia Pacific
PPG Industries
PPG Industries
Formosa Plastics
Formosa Plastics
Occidental Chemical
Location
Ingleside, TX
Convent, LA
Battleground, TX
Deer Park, TX
Plaquemine, LA
Baytown, TX
Wichita, KS
Mt. Vernon, IN
Burkville, AL
Geismer, LA
Freeport, TX
Plaquemine, LA
Muskogee, OK
Savannah River, GA
Green Bay, WI
Natrium, WV
Lake Charles, LA
Point Comfort, TX
Baton Rouge, LA
Niagara Falls, NY
Maximum 1-hour concentration (jig/m3)
Chlorine
AEGL-1= 2,900 ug/m3
25
99
20
47
2
24
137
10
2
1
156
346
5
10
3
155
83
25
130
153
HCI
AEGL-1 = 2,700 |ig/ms
—
10
41
1
90
61
0
—
—
_.
15
120
_.
—
_.
32
4
0
—
15
21
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other inputs used for this analysis, which were provided by the industry and checked by our staff,
are representative of the industry.
In this assessment, the predicted health effects estimated, using very conservative inputs
and assumptions, were well below the recognized health thresholds. While our approach in this
particular action may not be the same as an approach for a NAAQS, we believe that it has been
certainly more than cursory. We have looked at emissions and exposure data for each of the
sources in the subcategory. We have established hazard indices for chlorine and HC1 for each
source in the subcategory. We performed a qualitative ecological assessment. Moreover, in
response to comment received, we have revised our analyses and taken into account comments
that we have received when performing these re-assessments. We will base each risk assessment
for future regulatory action on sound scientific principles.
2.4.2 Receptor Locations
Comment: EPA requested comment on how to consider the 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. Two commenters (IV-D-06, F/-D-07) did
not agree with EPA's methodology for determining receptor location for threshold pollutants.
The commenters were concerned that people closer to the facilities would be harmed by
emissions from chlorine facilities. One commenter (TV-D-07) did not support EPA's use of
receptors placed at the center of census blocks within 2 kilometers of the site and in the
population-weighted centers of census block groups or census tracks out to 50 kilometers. The
commenter felt that it was more appropriate to measure the exposure of the most exposed
individual (e.g., someone living at the fence line of a facility or directly downwind). The
commenter maintained that EPA must set section 112(d)(4) standards at levels that allow no risk
or adverse health effects. According to the commenter, EPA's conclusion that most people
would not be harmed by emissions from chlorine facilities does not satisfy the requirements of
section 112(d)(4).
One commenter (TV-D-06) stated that EPA's methodology would be more appropriate for
cancer causing agent, where the risk is based on probabilities of health effects. The commenter
argued that for non-cancer (i.e., threshold pollutants) compounds, placing the receptors at the
center of census tracks would not properly identify the highest impacts close to the facility. The
22
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commenter stated that in the State of New York, the majority of stack heights at facilities that
emit chlorine or HC1 range from 40 to 70 feet high. The commenter further stated that stacks of
this height would have their greatest impacts near the facility (i.e., within 125 to 500 meters).
According to the commenter, an analysis out to 50 kilometers is unnecessary. The commenter
provided an analysis which identifies the maximum point of impact at 125 meters from the
facility using refined modeling. The commenter indicated that this would be a better
approximation of the possible ambient impacts due to EPA's decision to delist the source
category.
Response: We appreciate the input received on our request for comments, and we
certainly agree with the commenters that the greatest impacts will likely occur near the facility
for this source category. However, we do not agree with the commenters that our approach fails
to meet the statutory requirements of CAA section 112(d)(4). We do not feel that considering an
"ample margin of safety" means that we must demonstrate no risk or adverse health effects for a
theoretical person living at the fence line. Rather, we believe it is appropriate to assess the risks
at locations where people most likely reside. A census block is the smallest geographic unit for
which the Census Bureau tabulates 100-percent data. While census blocks in rural areas may be
larger, many blocks correspond to individual city blocks in more populated areas. The
commenter is correct in that an individual could live closer to the plant than the center of the
census block and our approach would have slightly underestimated risk. It is just as likely,
however, that the closest individual could live farther from the plant than the center of the census
block causing our risk estimates to be slightly overestimated. By placing receptors at the center
of populated census blocks on all sides of a facility, we have evaluated people living downwind.
In conclusion, we continue to feel that placing a receptor in the geographic center of populated
census blocks near a facility is a well established approach to exposure modeling which results in
a reasonable approximation of estimating the risks where people actually live, and we maintain
that this methodology is appropriate for actions taken under the authority of CAA section
112(d)(4) or CAA section 112(c)(9)(B)(ii).
2.4.3 EPA Has Underestimated Emissions
Comment: One commenter (TV-D-06) stated that the total chlorine and HC1 emissions
from some of the facilities included in the risk assessment were grossly underestimated. In
23
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support of their argument, the commenter pointed out potential inconsistencies in the background
emissions data contained in the docket. Specifically, the total chlorine emissions from the Dow
Chemicals, Freeport, Texas facility were reported in the risk assessment document6 to be
22 pounds per year (Ib/yr) but in the "Chlorine Production Summary Report,"7 chlorine
emissions from only one production process located at the Dow Chemicals facility (the
diaphragm cell process) were reported to be 9,800 Ib/yr. The commenter stated that since
emissions from other processes at the Dow facility were not included in the summary report, the
emissions were likely to be much higher. The commenter also noted that the Dow facility had
the lowest emissions (22 Ib/yr) of facilities reported in the risk assessment document and the
highest chlorine production volume (1.8 million Ib Cl2/yr), which also indicates that the
emissions from the Dow facility were underestimated.
According to the commenter, the inconsistencies between the reports undermine the
credibility of the risk assessment to support a decision to not regulate this source category.
Furthermore, the commenter stated that they believe that the emission inventory information
provides justification for a need to establish a MACT floor. The commenter concluded that the
risk assessment was flawed because the potential impacts on health and the environment were
underestimated.
Response: The primary sources of the emission estimates used in the risk assessment for
this source category were responses submitted directly by the facilities in response to a request
for information under our authority in section 114 of the CAA. A review of the data was
conducted as they were received, and followup questions asked of the industry representatives to
clarify the information submitted. After this analysis, we were satisfied with the quality of the
data, with one exception. Only one-half of the facilities submitted chlorine emission estimates
from fugitive sources. One of the areas of focus in the follow-up questions was to verify the
fugitive emission estimates for those facilities that did submit such estimates. Our conclusion
6 EC/R Incorporated. Chlorine Production Facilities Risk Assessment. Prepared for U.S.
Environmental Protection Agency. Research Triangle Park, NC. May 2002. (Air Docket A-
2002-09, Item No. FV-A-02).
7EC/R Incorporated. Chlorine Production Summary Report. Prepared for U.S.
Environmental Protection Agency. Research Triangle Park, NC. September 12,1996. (Air
Docket A-2002-09, Item No. IV-A-01).
24
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was that fugitive emissions are to be expected from every non-mercury cell chlorine production
plant, so we estimated fugitive emissions for those that did not submit estimates. This was done
using the highest emission factor calculated from the .plants that did report fugitives. We
believed that use of this "worst-case" factor was appropriately conservative for this assessment.
The commenter compared the emissions used in the assessment to 1991/1992 base year
emissions in an earlier report on this industry, the Chlorine Production Summary Report, and
correctly noted that there is a large discrepancy between the emissions levels for Dow
Chemical's plant in Freeport, Texas. As a result of this comment, we made a comparison of the
emissions from all plants between these two sources.8
The comparison revealed that the Dow Freeport facility is only one of only two plants
whose emissions used in the risk assessment were lower than the 1991/1992 base year emissions
in the 1996 summary report. In fact, the 2000/2001 emissions used in the risk assessment for the
other facilities with reported emissions in both documents average five times HIGHER than
those reported in the 1996 summary document. Clearly, this comparison does not lead to the
conclusion that the risk assessment was based on "grossly underestimated" emissions. A review
of the data submitted by the two facilities whose 2000/2001 emissions were substantially lower
than their 1991/1992 emissions did not result in any obvious errors or questionable assumptions
that could be disputed with the available information. Furthermore, according to the facility, the
chlorine and HC1 emissions reported in the 1996 summary document included emissions from
processes within the plant not related to chlorine production. That was corrected for the
2000/2001 emissions data submittal. Therefore, no changes were made as a result of the review
of the reported emissions data.
The comparison did result in the concern that the emissions, particularly the fugitive
emissions estimated using the worst-case factor, had been overestimated. As a point of
comparison, we obtained the 2001 chlorine releases from the Toxic Release Inventory (TRI) for
all ten sites for which fugitive emissions were estimated using the worst-case factor. We found
that nine of the ten plants had total chlorine fugitive releases reported in TRI that were less than
the those used in the risk assessment. For instance, for the PPG facility in Lake Charles,
8 Reference 1.
25
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Louisiana, reported that 8,000 Ib/yr of fugitive chlorine releases for the entire site (a very large
chemical complex). We estimated 31,178 Ib/yr using the worst-case emission factor. We
concluded that it was overly conservative to use these estimates in light of the TRI information
and in fact, we likely overestimated the fugitive emissions for these plants. Therefore, in the
revised modeling for chronic chlorine exposures discussed in 2.4.1, we used the total chlorine
fugitive releases from TRI for eight plants. That is still conservative as these TRI values
represent chlorine fugitive releases from all processes at the site, not just the non-mercury cell
chlorine production processes. For two plants, company representatives provided a breakdown
of the portion of the TRI emissions that were from the non-mercury cell chlorine production
processes and those values were used in the re-assessment.
2.4.4 Scope of the Risk Assessment
Comment: One commenter (IV-D-06) stated that all chlorine emissions from non-
mercury cell chlorine production facilities that are collocated with other source categories need to
be reviewed as a whole when evaluating public health risk, adverse environmental effects, and
possible control strategies. The commenter stressed that other sources of chlorine and HC1
should be included in the risk assessment under CAA section 112(d)(4). The commenter was
concerned that not accounting for all chlorine and HC1 emissions from a facility would provide
the community with a false sense of assurance of protection, and is not consistent with the
legislative intent of the CAA to consider cumulative HAP exposure issues through an integrated
approach under CAA sections 112(d), 112(f), and 112(k). Therefore, the commenter requested
that EPA evaluate the potential for adverse health and environmental impacts using conservative
risk assessment methodology that incorporates all known chlorine and HC1 emissions from a
contiguous facility.
Response: Section 112 of the CAA requires us to list categories and subcategories of
major sources and area sources of HAP and to establish NESHAP for the listed source categories
and subcategories. In directing us how to establish MACT emission limits, section 112(d)(3) of
the CAA requires us to set the emission limitation at a level that assures that all major sources
achieve the level of control at least as stringent as that already achieved by the better-controlled
and lower-emitting sources in each source category or subcategory. Therefore, the entire MACT
26
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program is structured on a source category-specific basis. All MACT standards developed to
date have addressed emissions from specific source categories.
There are instances where non-mercury chlorine production facilities are collocated with
other source categories. However, based on the risk assessment for chlorine and HC1 emissions
from chlor-alkali plants, the predicted impacts from chlorine and HC1 at these chlor-alkali plants
are extremely low. We believe that the human health and environmental impacts from all
sources in the category even when collocated with other chlorine and HC1 emissions will still be
within an ample margin of safety to protect the public health, and will not cause adverse
environmental effects. Moreover, as indicated in the preamble to the proposed rule, most major
processes at the sites where non-mercury cell chlorine production facilities are located are subject
to, or will be subject to, NESHAP to reduce HAP emissions (67 FR 44714, July 3,2002).
Therefore, it would not be appropriate to include emissions from those sources in an assessment
for the non-mercury cell chlorine production source category conducted under the authority of
CAA section 112(d)(4).
2.4.5 Ecological Assessment
Comment: Two commenters (TV-D-06, FV-D-07) stated that the environmental effects
analysis was not adequate. One commenter (TV-D-06) stated that potential ecological effects of
HC1 emissions have not been properly referenced. The commenter further remarked that since
total facility chlorine and HC1 emissions were not included hi the modeling, potential HCI
environmental effects have been discounted in the technical documentation.
One commenter (TV-D-07) stated that EPA's proposed action falls short of its obligation
to protect against environmental effects. According to the commenter, EPA has understated its
statutory obligation hi the proposed action. The commenter referred to the legislative history,
which indicates that CAA section 112(d)(4) requires standards that "would not result in adverse
environmental effects which would otherwise be reduced or eliminated."9 The commenter listed
the several shortcomings in the EPA's environmental assessment.
The commenter concluded that although EPA acknowledged that it had an obligation to
ensure that any standards set under CAA section 112(d)(4) did not have any adverse
9S. Rep. No. 228, 101st Cong., 1st Sess. (1989( at 171, 5 Leg. Hist. At 8511)
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environmental effects, the Agency did not properly consider the issue. Therefore, the commenter
stated that they believed that EPA could not promulgate standards under CAA section 112(d)(4)
without contravening the CAA.
Response: While CAA section 112(d)(4) makes no mention of environmental effects, we
took the potential of such adverse effects into account when we issued our proposed action, hi
addition, CAA section 112(c)(9)(B)(ii), which is the authority under which we have cited the
decision to delete this subcategory, does require that we show there are no adverse environmental
effects from emissions from the subcategory.
We believe that the level of our analysis at proposal was adequate to demonstrate the
requirements of CAA section 112(c)(9)(B)(ii). The commenters did not even suggest that they
believed there was the potential for adverse environmental effects from HC1 or chlorine
emissions from non-mercury cell chlorine production plants. Were there any evidence that such
adverse effects were likely, or even possible, we would have conducted a more intensive
ecological risk assessment.
The commenters are correct, however, that we did not discuss the ecological effects of
chlorine. This was because, as was stated hi the proposal preamble, we did not perform a
separate evaluation of chronic chlorine exposure because chlorine is converted to HC1 in the
atmosphere so rapidly. Following is a brief summary of the environmental effect of chlorine.
Atmospheric exposure is the primary pathway that environmental effects from chlorine
emissions. However, since most chlorine is converted to HC1, studies have focused on the
effects of HC1 on vegetation. Although plant exposures to elevated levels of chlorine can cause
plant injury, it tend to be converted to other, less toxic forms rather rapidly in plants, and may not
result in the direct accumulation of toxic pollutant residuals important in the food chain.
Plant studies have found foliar damage due to chlorine emissions and foliar damage,
decreased levels of chlorophyll a and b, decreased leaf areas, obvious chlorosis, and a decline in
fruit production due to chlorine emissions. Plants exposed to HC1 mist in a laboratory also
showed foliar damage and decreased chlorophyll levels.
There is evidence of effects to animals due to accidental and/or catastrophic exposures,
but the chlorine concentrations of these exposures are unknown. However, there is no data on
exposures to historic or atmospheric concentrations.
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More information is available on the effects of chlorine from aquatic exposures.
However, there is no evidence that suggests that emissions of chlorine from industrial sources in
the air contribute significantly to aquatic concentrations of chlorine.
One study reported that growth of phytoplankton was inhibited after 10 to 20 minutes of
exposure to chlorinated cooling waters with total residual chlorine (TRC) levels less than
0.15 milligram per liter (mg/L). Another study reported reduced carbon uptake and chlorophyll a
activity in phytoplankton exposed for 30 minutes to 0.1 to 1.0 mg/L, and that the photosynthetic
system was destroyed when exposed to TRC greater than 1.0 mg/L. Additional laboratory
studies showed that continuous exposure to 0.002 mg/L TRC resulted in depressed algal biomass
in naturally-derived microcosms.
When exposed continuously for 96 hours to 0.05 mg/L TRC, the Eurasian water milfoil
showed a significant reduction in shoot and dry weights and a 16-percent decrease in shoot
length. In addition, at concentrations of 0.1 mg/L, chlorophyll levels decreased by 25 percent
Aquatic invertebrates are very sensitive to chlorine and reaction products of chlorine,
with early life stages showing the most sensitivity. For example, free chlorine, monochloramine,
and dichloroamine have been shown to reduce the rate of oyster larvae survival. Many studies
have been performed, and the results are highly variable depending on the chlorine species, the
lifestage of the invertebrate, and other factors such as salinity. The most sensitive aquatic species
appears to be molluscan larvae, with LC50 concentrations of 0.005 mg/L. Sublethal effects have
also been studied, including reduced growth, reduced motility, and reproductive failure.
The effects on fish also vary depending on the life stage and fish species, and
environmental factors, such as the pH, temperature, and type of chlorine species. Larval stages
are more susceptible to effects, and freshwater species are more sensitive than marine species.
The most sensitive fish appears to be salmonids. One study showed a 50-percent increase in
toxicity when the temperature rose from 10°C to 30°C. Free chlorine is generally more toxic
than residual chlorine; where the form of chlorine is dependent on the pH of the water. Sublethal
effects such as avoidance, reduction of diversity in chlorinated effluents, reduction or elimination
of spawning, abnormal larvae, reduced oxygen consumption, and gill damage have been noted.
Many LC^ values were reported, ranging from 0.08 mg/L after 24 hours of exposure to TRC to
2.4 mg/L after 0.5 hours of exposure to TRC.
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In the soil, chlorine is oxidized or degraded and is not likely to accumulate. Sediments
below pulp and paper mill effluents have contained chloro-organics, which could indicate that
chlorine reaction products linger in the environment. And, animal tissue can potentially
accumulate organics. Chlorine gas can accumulate in plant tissues, but has not been shown to
biomagnify.
Acute and chronic exposures to predicted chlorine and HC1 concentrations around the
sources are not expected to result in adverse toxicity effects. These pollutants are not persistent
in the environment. The chlorine and HC1 emitted should not significantly contribute to aquatic
chlorine concentrations, and are not likely to accumulate in the soil. Chlorine rapidly converts to
HC1 in the atmosphere, and chlorine and HC1 are not believed to result in biomagnification or
bioaccumulation in the environment. Therefore, we do not believe there will be adverse
ecological effects due to chlorine and HC1 emissions from non-mercury cell chlorine production
plants.
2.5 OTHER COMMENTS
Comment: One commenter (IV-D-04) referred to EPA's statement that "most chlorine
production facilities are covered under section 112®) of the CAA for the prevention of accidental
releases of chemicals. The commenter (TV-D-04) stated that they are not aware of any chlor-
alkali production facilities that are not covered by section 112®).
Response: The commenter is correct. All chlor-alkali plants are subject to standards
developed under section 112®) of the CAA.
Comment: One commenter (TV-D-07) stated that EPA is wasting time trying to avoid
promulgating standards that are almost two years overdue, rather than moving expeditiously to
comply with the CAA. The commenter stressed that EPA has broken the law by failing to
promulgate standards for the chlorine production source category. Should EPA continue to
evaluate section 112(d)(4) exemptions will ultimately lead to an unlawful rule.
Response: As stated in response to other comments, we believe that our action is clearly
in compliance with the CAA and that failing to promulgate standards is within our authority, and
indeed, appropriate and responsible, given the results of the associated risk assessments
conducted for this industry.
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