NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS ( NESHAP) FOR THE MERCURY CELL CHLOR ALKALI CHLORINE PRODUCTION INDUSTRY:

Summary of Public Comments and Responses EPA 453/ R 03 012 August 2003 National Emission Standards for Hazardous Air Pollutants ( NESHAP) for the Mercury Cell Chlor Alkali 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 v 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). vi vii ENVIRONMENTAL PROTECTION AGENCY National Emission Standards for Hazardous Air Pollutants for the Mercury Cell Chlor Alkali Chlorine Production Industry   Background Information for Promulgated Standards Prepared by:

_____________________________________ _______________________ Steve Fruh ( Date) Group Leader, Metals Group Emission Standards Division U. S. Environmental Protection Agency Research Triangle Park, NC 27711 1. The final National Emission Standards for Hazardous Air Pollutants ( NESHAP) will regulate emissions of hazardous air pollutants from mercury cell chlor alkali chlorine production operations. Only those operations that are part of major sources under section 112( d) of the Clean Air Act as amended in 1990 will be regulated.

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. Iliam Rosario Metals Group ( C439 02) U. S. Environmental Protection Agency Research Triangle Park, NC 27711 Telephone: ( 919) 541 5430 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 viii 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/ ttn ix TABLE OF CONTENTS 1.0 SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 SIGNIFICANT COMMENTS AND CHANGES SINCE PROPOSAL . . . . . . . . 1 2.0 SUMMARY OF PUBLIC COMMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 GENERAL COMMENTS ON THE PROPOSED RULE . . . . . . . . . . . . . . . . . . 7 2.2 APPLICABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.1 Comments on Title V Permitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.2 Comments Regarding the HAP addressed by the Proposed Rule . . . . . . 13 2.3 COMPLIANCE DATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.4 EMISSION LIMITATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.5 WORK PRACTICE STANDARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.5.1 Format of Fugitive Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.5.2 Comments on Work Practice Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.5.3 Cell room monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 2.6 TEST METHODS, PROCEDURES, AND REQUIREMENTS . . . . . . . . . . . . 61 2.7 CONTINUOUS COMPLIANCE DEMONSTRATION . . . . . . . . . . . . . . . . . . 65 2.8 RECORDKEEPING AND REPORTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 2.9 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 2.10 ECONOMIC AND BENEFITS ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . 74 x 1 1.0 SUMMARY 1.1 BACKGROUND On July 3, 2002, the U. S. Environmental Protection Agency ( EPA) proposed national emission standards for hazardous air pollutants ( NESHAP) for mercury emissions from mercury cell chlor alkali plants ( 67 FR 44672) under the authority of section 112 of the Clean Air Act ( CAA). Public comments were requested on the proposal in the Federal Register. Six 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 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 revisions made to the NESHAP between proposal and promulgation.

1.2 SIGNIFICANT COMMENTS AND CHANGES SINCE PROPOSAL In response to comments received on the proposed standards, several changes have been made to the final rule. While several of these changes are clarifications designed to make the Agency's intent clearer, EPA has made a number of more substantive changes to the final rule in direct response to comments received. A summary of the changes made since the proposal are described in the following sections. Detailed Agency responses to public comments and the revised analysis for the final rule are contained in section 2 of this document.

The proposed rule contained a compliance date 2 years from the date that the final rule would appear in the Federal Register. In the final rule, the compliance date has been changed to 3 years from the date of publication of the final rule in the Federal Register. However, unlike the proposed rule, which would have required that performance tests be conducted within 180 days after the compliance date, the final rule requires that all performance tests be conducted on or before the compliance date. 2 TABLE 1 1. LIST OF COMMENTERS ON PROPOSED NATIONAL EMISSIONS STANDARDS FOR HAZARDOUS AIR POLLUTANTS Docket Numbera Commenter and Affiliation IV D 01 Mr. Arthur E. Dungan Vice President  Safety, Health and Environment The Chlorine Institute, Inc. 200 l Street, N. W. Washington, DC 20036 4919 IV D 02 Ms. Cynthia Sarthou Executive Director Gulf Restoration Network Mr. Barry Kohl Conservation Chair Louisiana Audubon Council Ms. Norma Gavin President League of Women Voters of Louisiana IV D 03 Mr. David C. Foerter Deputy Director Institute of Clean Air Companies ( ICAC) 1660 L Street NW, Suite 1100 Washington, DC 20036 5603 IV D 04 Mr. Robert G. Smerko President The Chlorine Institute, Inc. Washington, DC 20036 4919 IV D 05 Mr. Samuel Z. Chamberlain Vice President Environment, Health & Safety Pioneer Americas LLC IV D 06 Mr. Neil S. Kagan Senior Counsel National Wildlife Federation 213 West Liberty Street, Suite 200 Ann Arbor, MI 48104 TABLE 1 1. LIST OF COMMENTERS ON PROPOSED NATIONAL EMISSIONS STANDARDS FOR HAZARDOUS AIR POLLUTANTS ( continued)

Docket Numbera Commenter and Affiliation 3 IV D 07 Mr. Steven F. Faeth Law Department PPG Industries Inc. One PPG Place Pittsburgh, PA 15272 Comment Letters Received After the Close of the Comment Period IV G 01 Ms. Linda E. Greer Senior Scientist Mr. Jon P. Devine, Jr. Senior Attorney Natural Resources Defense Council IV G 02 Mr. Jon P. Devine, Jr. Senior Attorney Natural Resources Defense Council 4 For mercury cell chlor alkali production facilities affected sources, the proposed rule included a single emission limitation that covered all mercury emissions from the two point sources associated with chlorine production in mercury cells: the by product hydrogen stream and the end box ventilation system vent. The format of this limitation was total grams of mercury per Megagram of chlorine production ( g Hg/ Mg Cl 2). For the initial compliance determination,

the aggregate mercury emissions from all hydrogen by product streams and all end box ventilation system vents were divided by the chlorine production for the same period and compared with the applicable emission limitation. Continuous compliance would have then been demonstrated by continuously monitoring the mercury concentration in each stream and comparing the daily average mercury concentration against a level determined during the initial compliance test.

Commenters objected to this daily averaging period for compliance purposes when the emission limitations were based on annual average emissions and chlorine production. In response to these comments, we have written the averaging time for continuous compliance as a 52 week period.

Further, as discussed more below, rather than establishing surrogate mercury concentration operating limits for each vent, continuous compliance is determined by a direct comparison of the emissions per unit of chlorine production ( g Hg/ Mg Cl 2) for each 52 week compliance period and the emission limitation. This is a rolling average compliance period that is determined each week.

That means a compliance determination is required each week for the previous 52 week period.

In addition to the averaging time for the by product hydrogen/ end box ventilation system vent, we changed the value of the emission limitation for plants with end box ventilation systems from the proposed limit of 0.067 g Hg/ Mg Cl 2 to 0.076 g Hg/ Mg Cl 2. The proposed limit of 0.033 g Hg/ Mg Cl 2 for plants without end box ventilation systems is retained in the final rule.

In the final rule, we have written the method for determining continuous compliance for the point sources of emissions in both types of affected sources covered by the rule ( by product hydrogen streams and end box ventilation system vents at mercury cell chlor alkali production facilities and mercury thermal recovery unit vents at mercury recovery facilities). In the proposed rule, performance tests would have been required to determine initial compliance with the applicable emission limitation. The proposed rule also would have required that the mercury concentration of each vent be monitored during these performance tests, and that a mercury concentration operating limit be established for each vent based on the monitoring results 5 obtained during the test. Compliance with the emission limitation would have then been determined by comparing the results of the continuous monitoring of mercury concentration against the established operating limits. There were several comments received on this approach.

In response to these comments, continuous compliance in the final rule is determined via a direct comparison of emissions to the emission limitation rather than using mercury concentration operating limits as a surrogate. For by product hydrogen streams and end box ventilation system vents, the aggregate mercury emissions will be determined, divided by the corresponding chlorine production, and compared with the emission limitation for each 52 week compliance period ( as discussed above). For mercury thermal recovery unit vents, the measured mercury concentration will be directly compared against the emission limitations ( which are in units of milligrams of mercury per dry standard cubic meter, or mg/ dscm). Also, the final rule contains two options for measuring the mercury emissions for continuous compliance: continuous mercury emission monitoring systems, and periodic sampling using EPA reference methods or approved alternative methods.

The proposed work practice provisions included a cell room monitoring program, which would have required that the mercury concentration be monitored in the cell room and corrective action taken when a plant specific action level was exceeded. The final rule retains the cell room monitoring program, but it is as an alternative to the work practices. The optional cell room monitoring provisions in the final rule are more detailed and prescriptive than the requirements in the proposed rule, and the final rule requires the preparation and submittal of site specific cell room monitoring plans. Since the cell room monitoring program was made optional, the final rule requires ( if optional cell room monitoring is not chosen) the owner or operator to institute a floor level mercury vapor measurement program. This program is designed to limit the amount of mercury vapor in the cell room environment through periodic measurement of mercury vapor levels.

The final rule also requires that the owner of each mercury cell chlor alkali plant report the mass of virgin mercury added to the cells. Initial compliance with this requirement is demonstrated by reporting the mass of mercury added to cells for the 5 years preceding the compliance date. This is a requirement requested by commenters. 6 7 2.0 SUMMARY OF PUBLIC COMMENTS A total of nine written comments were received on the proposed standards, two of which were received well after the close of the public comment period. The following sections provide a summary of these comments, as well as the Agency's responses to these comments. For the purpose of orderly presentation, the comments have been categorized under the following topics:

° General Comments on the Proposed Rule ° Applicability ° Compliance Date ° Emission Limitations ° Work Practice Standards ° Test Methods, Procedures, and Requirements ° Continuous Compliance Demonstration ° Recordkeeping and Reporting ° Definitions ° Economic and Benefits Analysis 2.1 GENERAL COMMENTS ON THE PROPOSED RULE Comment: Commenters IV D 02 and IV D 03 supported the proposed standards. One commenter ( IV D 02) noted that the proposed rule will benefit public health and produce much needed reductions in mercury releases in the State of Louisiana and nationwide. Another commenter ( IV D 03) supported EPA's basic reliance on proven, cost effective, and readily available air pollution control and monitoring technologies.

Response: We appreciate the commenters' support and are finalizing work on this source category with the goals of benefitting public health and relying on proven technologies in mind, as well as meeting the requirements of the CAA.

Comment: One commenter ( IV D 03) supported EPA's emission limits as proposed,

stating that such limits are needed to achieve the emission reductions of 1,225 pounds per year relative to actual emissions and the 7,500 pounds per year relative to potential emissions that would result from a relatively few facilities. The commenter agreed that it is feasible and costeffective to achieve the proposed mercury emission limits for facilities with and without end box ventilation systems using existing control and upgraded technologies, including new and upgraded installations of carbon adsorbers and scrubbers. Specifically, the commenter supported EPA's proposed conclusions that retrofit control equipment is practical and reasonable and that reliance on beyond the floor control options is warranted. 8 Response: We appreciate the commenter's support and agree that the application of control technologies and the use of work practice standards can reduce the emissions of mercury to the environment.

Comment: A commenter that submitted comments after the close of the comment period ( IV G 01) believed that EPA missed the opportunity to eliminate significant industrial mercury emissions by not banning, or even significantly reducing, mercury emissions and they recommended that EPA re define MACT to ban the use of mercury cell technology. The commenter explained a ban of mercury cells would be easily achievable because the majority of the chlorine production industry already uses other, superior technologies such as membrane cells and diaphragm cells. The commenter noted that the mercury cell chlor alkali industry is in a demise, citing the fact that only ten plants currently exist, down from 30 in 1970, and that these plants are each approaching the end of their useful life because they were built in the 1960' s. The commenter further noted that each company which operates a mercury cell plant also produces chlorine via other, cleaner, more efficient methods. The commenter concluded that EPA should have required a phase out of mercury cell chlor alkali production to expedite the elimination of mercury emissions from this industry rather than propose a weak regulation with many gaps and loopholes.

The commenter asserted that there is an urgent need to reduce the amount of mercury used and released into the environment because mercury is a " notorious neurotoxin" which has a particularly negative effect on the neurological development of fetuses and young children. The commenter explained that methyl mercury, which is the most toxic form, is produced by bacteria from the metallic form in which it is typically emitted and that the most significant route of exposure to methyl mercury is through consumption of fish which have bioaccumulated the toxin via the food chain. The commenter cited strong recommendations by various organizations that women of childbearing age and children under six years of age should avoid certain seafood, as well as studies on the relatively high amounts of methyl mercury in newborns and women of childbearing age, as examples of the widespread consensus that existing levels of mercury in the environment pose serious harm.

The commenter stated that EPA could still ban the mercury cell process by setting MACT above the floor. The commenter estimated that a reasonable total cost for MACT which would 9 still be cost effective according to EPA guidelines would be $ 1.5 billion, based on an analysis of other MACT standards. The commenter estimated that the cost to convert all mercury cell plants to other technologies would be approximately $ 920 million and concluded that this above

thefloor cost was justifiable, especially given the beneficial non air quality health and environmental impacts that would result.

Finally, the commenter cited a lack of confidence that the mercury cell process could be adequately controlled as a reason to ban the use of the mercury cell process. The commenter explained that EPA had been unable to accurately quantify fugitive emissions, which are the largest source of mercury emissions from mercury cell chlor alkali plants, and consequently unable to issue a numerical emission limitation. The commenter complained that the work practice requirements which are proposed instead to address fugitive emissions are too weak and rely on vague practices and undefined time scales. Taking into account EPA's insistence that these requirements could not be changed, the commenter concluded that the proposed rule offered very limited protection of public health and the environment.

Response: While the facts cited by the regarding the demise of the mercury cell chloralkali industry are correct, we disagree with the with their arguments that the rule should ban mercury cell chlor alkali plants. We do believe, however, that the final rule contains a means of " phasing out" mercury cell technology by not allowing prohibiting mercury emissions from new or reconstructed sources. This effectively bans the construction of new mercury cell plants, as well as the reconstruction of existing mercury cell plants.

We agree with the commenter's evaluation of the health effects of mercury. However,

these significant effects do not provide a legal justification for banning all mercury cell chlor alkali plants under section 112( d).

We do not believe that the commenter's point that the mercury cell process should be banned because it is cost effective to do so is entirely accurate. First, the commenter did not provide any basis for their cost estimates so we could not verify these costs. Further, we do not believe that " conversion" accurately describes the replacement of a mercury cell plant to another technology. There is little salvageable from a mercury cell plant that can be used in the construction of a membrane cell plant, so the demolition of the mercury cell plant followed by the construction of a membrane cell plant is a more accurate characterization. 10 We believe the commenter's final argument is not supported by the statutory authority provided in section 112( d)( 2), which is the basis for the final rule. In general, section 112( d)( 2)

requires that level of control for the entire industry be established based on the best controlled facilities. The fact that there is there is inadequate control would lead to less stringent, not more stringent, standards. We do acknowledge that we are unable to issue a numerical emission limitation for fugitive emissions, as discussed in section 2.5.1. However, we disagree that the work practice standards are too weak and rely on vague practices and undefined time scales.

Rather, we believe that they will be effective practices to identify and correct sources of fugitive mercury emissions.

In conclusion, we did not take the commenter's suggestion and ban the use of mercury cell technology. We believe that the final rule will achieve real reductions in mercury emissions and will provide public health and environmental benefits.

2.2 APPLICABILITY 2.2.1 Comments on Title V Permitting Comment: Three commenters ( IV D 04, IV D 05, IV D 07) disagreed with the proposed requirements for all mercury cell chlor alkali plants to obtain a title V permit, including area sources. The commenters requested that this provision be deleted from the final rule. The commenters stated that most facilities affected by the proposal are minor sources of HAP emissions and maintained that requiring minor source facilities to obtain title V permits would impose a burdensome paperwork requirement ( including duplicative reporting and recordkeeping)

that would yield no environmental benefit. According to commenter IV D 05, dropping the title V permit requirement would not lessen any substantive requirements for monitoring,

recordkeeping, or operation of any and all air pollution control devices. Commenters IV D 04 and IV D 07 noted that the CAA allows EPA to exempt certain sources from obtaining a title V permit ". . . if the Administrator finds that compliance with such requirements is impracticable,

infeasible, or unnecessarily burdensome . . .."

Commenter IV D 07 noted that in previously promulgated area source MACT standards ( e. g., Dry Cleaning MACT and Halogenated Solvent Cleaning MACT), EPA identified area sources as being subject to title V permitting. However, EPA allowed the permitting authorities to defer area sources from title V permitting requirements until December 9, 2004. 11 In contrast, Commenter IV G 1 ( which submitted comments after the close of the comment period) supported the proposed requirement to require all affected sources to obtain title V permits. The commenter argued that title V permits are needed because they consolidate sources' applicable requirements in a single place. The commenter further noted that ". . . given the detailed work practice requirements, it is reasonable to expect significant source specific tailoring of the standard for each plant's individual configuration." See, e. g., 67 FR 44706 07.

The commenter also stated that requiring title V permits of area sources of mercury is especially appropriate because a small quantity of mercury is as toxic as a far greater amounts of other HAP.

Response: Section 502( a) of the CAA requires any source, including an area source,

subject to standards or regulations under section 112 of the CAA to operate in compliance with a title V permit after the effective date of any title V permits program. Section 502( a) states that the Administrator may promulgate regulations to exempt one or more source categories, in whole or in part, from the requirements of the section if the Administrator finds that compliance with title V requirements is impracticable, infeasible, or unnecessarily burdensome on such categories.

The Administrator may not exempt any major source from the requirements of title V.

Three commenters disagreed that area sources under the final rule should be required to obtain title V permits. In order to exempt area sources under the final rule from title V requirements, the test in section 502( a) of the CAA must be met. Specifically, the Administrator must make a finding that title V requirements are impracticable, infeasible, or unnecessarily burdensome for the source category or categories in question. Commenters may provide data which would help the Administrator make such a finding, but the commenters who were opposed to area sources being permitted under the final rule did not provide any such data. Commenters providing supporting data for their arguments is consistent with what the Agency stated in its final rule for the Municipal Solid Waste Landfills NESHAP in reference to the test in section 502( a) of the CAA: " If commenters choose to try and meet this test when commenting on a proposed section 111 or 112 standard, they must submit comments which document in detail the ways in which the title V requirements are impracticable, infeasible, or unnecessarily burdensome for the source category in question." ( See footnote 1 68 FR 2227, 2234, January 16, 2003).

In terms of the commenters' concern about title V adding duplicative recordkeeping and reporting requirements, the only potential duplicative requirement that we are aware of is in 12 relation to deviation reporting under the semiannual compliance report required by § 63.8254 of the final rule and the semiannual monitoring report required by 40 CFR 70.6( a)( 3)( iii)( A) or 40 CFR 71.6( a)( 3)( iii)( A). However, this potential duplication was addressed by § 63.8254( d) in the proposed rule and this has been clarified in the final rule.

As to the deferral for area sources subject to the Dry Cleaning MACT and the Halogenated Solvent Cleaning MACT, the area sources subject to these MACT standards were deferred from title V permitting until December 9, 2004 ( 64 FR 69637, December 14, 1999).

This deferral was granted in part because of the concern that area sources would not be able to obtain the technical and procedural assistance from permitting authorities needed to file timely and complete title V applications given that permitting authorities would be focused on the permitting of major sources. However, as the title V program is no longer in its initial stages and the initial permitting of existing major sources is nearing completion, we would not be justified in granting a deferral to area under the final rule for the same reason.

In terms of the commenter who supported the permitting of affected sources under the final rule, we agree that the consolidation of requirements in a title V permit is one of the ways that title V helps assure compliance with all applicable requirements. As this commenter also pointed out, title V permits clarify which requirements in standards apply to a source where requirements may vary due to various factors, e. g., design of the facility. Additionally, the title V regulations at 40 CFR part 70 and 40 CFR part 71 help a source assure compliance with its applicable requirements by requiring that a source self certify to compliance initially and annually,

by requiring that a source promptly report deviations from its permit requirements, and by requiring that a permit contain monitoring requirements. It is also important to note that the title V permitting process provides an opportunity for the public to comment on whether a source is complying with its applicable requirements. In short, title V permits can enhance the effectiveness of rules such as the final rule, and EPA, therefore, disagrees that there are no environmental benefits to requiring title V permits for area sources.

In conclusion, as the test in section 502( a) of the CAA has not been met, EPA has retained the requirement in the final rule that affected sources subject to the final rule must obtain title V permits. Therefore, whether an affected source under the final rule is a part of a major or area source, the major/ area source is required to obtain a title V permit. 13 2.2.2 Comments Regarding the HAP addressed by the Proposed Rule We divided the chlorine production category into two subcategories: mercury cell chloralkali plants, and chlorine production plants that do not rely upon mercury cells for chlorine production ( diaphragm cell chlor alkali plants, membrane cell chlor alkali plants, etc). On July 3,

2002, we issued separate proposals to address the emissions of mercury from the mercury cell chlor alkali plant subcategory sources ( 67 FR 44672) and the emissions of chlorine and HCl from both the non mercury cell chlorine production subcategory sources and the mercury cell chloralkali subcategory sources ( 67 FR 44713). Specifically, we proposed a rule for mercury emissions from mercury cell chlor alkali plants, and we proposed not to regulate chlorine and HCl emissions from mercury cell chlor alkali plants and non mercury cell chlorine production plants under our authority in section 112( d)( 4) of the CAA.

Comments were received regarding the proposed action not to regulate chlorine and HCl emissions ( see Air Docket OAR 2002 0016 or Air Docket A 2002 09). The aspects of these comments related to the mercury cell chlor alkali plant subcategory can be generally classified into two basic categories: our statutory authority under section 112( d)( 4); and the site specific risk assessments that formed the basis for our decision.

<IP_ADDRESS> Comments Related to the Section 112( d)( 4) Authority Comment: Several comments were received related to our decision not to regulate chlorine and HCl emissions from chlorine production under the authority of section 112( d)( 4).

Some commenters supported this decision and stated the interpretation of our 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 stated that EPA should use its authority under section 112( c)( 9)( B)( ii).

Five commenters ( IV D 01, IV D 02, IV D 03, IV D 04, IV D 05) supported EPA's decision not to regulate chlorine and HCl emissions from non mercury cell chlorine production plants under the authority of section 112( d)( 4). One commenter ( IV 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 ( IV D 04), any further regulation of chlorine and HCl emissions from the chlorine production industry would have no environmental benefits, but would result in costs for 14 monitoring, recordkeeping, and reporting efforts to certify compliance with any requirements.

The commenter ( IV D 04) was concerned that a regulation would also stretch EPA's limited resources in monitoring for compliance. Three commenters ( IV 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 Congress included section 112( d)( 4) in the CAA to prevent unnecessary regulation of source categories. One commenter ( IV D 02) 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).

Three commenters ( IV D 06, IV D 07, and IV 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 ( IV 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 ( IV 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 in 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).

The commenter also referred to section 112( d)( 1), stating 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 112( 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 15 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 were created. The commenter requested that EPA perform a MACT floor analysis and develop a NESHAP for new sources.

Two of the commenters ( IV D 03, IV D 05) stated that EPA should support its decision not to regulate the chlorine production source category by citing the provisions of section 112( c)( 9)( B)( ii) in addition to the provisions of section 112( d)( 4). The commenters stated that the evaluation performed by EPA would also be sufficient for deleting sources under section 112( 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. Therefore, in addition to using the authority under section 112( d)( 4), the commenters suggested that EPA delete the subcategory using the authority under section 112( c)( 9)( B)( ii) to avoid any uncertainty over the use of its authority under section 112( d)( 4).

Response: The EPA has the authority under CAA section 112( d)( 4) to decide not to establish a NESHAP for chlorine and HCl emissions from certain chlorine production facilities.

We have decided to limit our use of section 112( d)( 4) to the emissions of chlorine and HCl from sources within the mercury cell chlor alkali subcategory. While we have decided to establish no standards for the emissions of these two HAP from sources in the mercury cell chlor alkali plant subcategory, we are establishing standards for the mercury emissions from the sources within that subcategory. As explained elsewhere in today's Federal Register, we have decided to delete the non mercury cell chlorine production plants subcategory under CAA section 112( c)( 9)( B)( ii).

The only HAP emitted by the non mercury cell chlorine production sources are chlorine and HCl.

Contrary to other commenters claims that our use of section 112( d)( 4) is inappropriate,

both the statutory language and the legislative history of the provision support our decision not to set limitations for chlorine and HCl emissions from sources in the mercury cell chlor alkali plant subcategory. The language of section 112( d)( 4) provides the Agency with ample discretion to utilize a risk based approach in determining whether to establish emission standards for those HAP where we determine that the HAP are " threshold pollutants" and that the standard ( or no standard) will achieve an " ample margin of safety." 16 The statutory language in section 112( d)( 4) is ambiguous. Thus, under the Supreme Court's decision in Chevron v. NRDC, 467 U. S. 837 ( 1984), the Agency has the discretion to interpret the language to allow us to establish NESHAP that do set limitations on certain HAP emitted from sources (" when establishing standards") but to also decide not to set limitations on other HAP emitted from these same sources if the other HAP are threshold pollutants and the risk from the emissions are so low that no standard for that second set of HAP is necessary to protect the public and the environment with " an ample margin of safety."

This approach is consistent with prior decisions EPA has made in the context of two other NESHAP. First, in the NESHAP for combustion sources at pulp mills ( 40 CFR part 63, subpart MM), we chose not to set a standard for HCl emissions from recovery furnaces, while we did set standards for other HAP emitted from the same sources within the category. We explained this decision in the preamble to the proposed MACT standard and received no adverse comment on the approach ( 63 FR 18754, 18765 68, April 15, 1998). Second, we proposed to set no standard under section 112( d)( 4) for HCl emitted from lime kilns, while we also proposed to set standards for other HAP emitted by these same sources ( 67 FR 78046 December 20, 2002). We also received no adverse comment on that proposed decision. While we originally proposed to utilize section 112( d)( 4) to set no standard for chlorine and HCl from chlorine production sources in a separate notice of the Federal Register ( 67 FR 44713, July 3, 2002), we made it clear that the proposed use of section 112( d)( 4) would apply to emissions of these two HAP from mercury cell chlor alkali sources ( as well as the emissions of chlorine and HCl from other chlorine production sources).

We do not agree that Congress' use of the phrase " in lieu of" in CAA section 112( d)( 5) so clearly restricts any possible interpretation of CAA section 112( d)( 4) such that some form of a MACT standard must always be set even when the criteria of section 112( d)( 4) are met. Instead,

we interpret that Congress enacted section 112( d)( 4) to provide EPA with the discretion to take risk into account and decide that standards need not be set when the HAP are threshold pollutants and levels being emitted are below the threshold value with an ample margin of safety. Moreover,

in each case where we have exercised authority under section 112( d)( 4), we have established standards in each category ( or subcategory, as here) for those pollutants that do not satisfy the threshold pollutant and ample margin of safety statutory criteria. 17 We also disagree with the commenter who argued that the provision in section 112( c)( 2),

which requires the Administrator to establish emission standards for listed categories and subcategories, has much bearing on our use of section 112( d)( 4) in this circumstance. By setting a standard for the emission of mercury from the mercury cell chlor alkali plant subcategory, we are fulfilling our obligations under section 112( c)( 2). As stated earlier, we have utilized the same approach in our other uses of section 112( d)( 4), e. g., HCl emissions from combustion sources at pulp mills and lime production sources.

The statutory language in section 112( d)( 1) and ( 3) does not prevent us from deciding that no emission standard is necessary for a particular threshold pollutant which is being emitted at levels well below the ample margin of safety when we are also establishing standards for HAP emitted from sources in that same category or subcategory. This approach to our use of section 112( d)( 4) is consistent with the statutory language of section 112( d)( 1) and ( 3). We are establishing emission standards for the listed category or subcategory, but are deciding that no MACT floor need be established and no emission standard set for those HAP that meet the criteria of " threshold pollutant" and " ample margin of safety."

With regard to the concerns the commenter raised about the failure to set a standard for new sources, our review of the mercury cell subcategory indicates that no new mercury cell chloralkali plants will be constructed. Given that our emission standard for new sources in the mercury cell chlor alkali subcategory prohibits the emission of mercury, we do not believe any new sources using mercury cells for chlorine production will ever be constructed ( or reconstructed).

Therefore, this no mercury emissions requirement in the final rule will, in effect, also ensure that there are no chlorine or HCl emissions from new mercury cell facilities.

In response to other commenters' suggestion that we utilize the authority of section 112( c)( 9)( B)( ii) to delete the chlorine production category, we have decided to exercise our authority under that statutory provision for the non mercury cell chlorine production subcategory.

That decision is discussed in a separate notice in today's Federal Register. However, we are not deleting the mercury cell chlor alkali plant subcategory because the sources within the category also emit mercury, and we are establishing emissions standards for mercury emissions in today's final rule. 18 Comment: Some commenters ( IV D 07, IV D 08) concluded that we did not establish either cancer or noncancer thresholds for HCl and chlorine and, therefore, it is illegal for EPA to attempt to use section 112( d)( 4) to set standards.

Response: The " threshold level" in section 112( d)( 4) refers to the level of concentration of a chemical under which no health effects are expected from exposure, although this term is not defined in section 112. Further, section 112 does not address the process that must be followed to " establish" a threshold level.

The reference concentration ( 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 (

g/ m3) is an appropriate threshold value for assessing risk to humans associated with exposure to HCl 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 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 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

g/ m3 used in our revised analysis. Chlorine has also been assigned AEGL values ( 62 FR 58840), including the 1 hour AEGL1 of 1,500

g/ m3 used in our revised analysis. 19 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 HCl and chlorine.

Further, the recognition of these levels by EPA, ASTDR, and CAL EPA indicates that chlorine and HCl are threshold pollutants.

Moreover, we provided the public an opportunity to comment on the thresholds for chlorine and HCl that we used in our original analysis for the proposed action ( 67 FR 44716).

We used the same threshold level for HCl for both the proposed and final NESHAP for the pulp and paper mill category. We have also used the same threshold for HCl in the proposed and final NESHAP for lime production ( 67 FR 78046; final action is anticipated in August 2003). There is no requirement in section 112( d)( 4) that EPA develop or finalize a threshold for a particular HAP in a certain manner. The thresholds we have used for both HCl and chlorine are consistent with the statutory language in section 112( d)( 4).

<IP_ADDRESS> Comments Related to the Risk Assessment Comment: In the analysis for the proposed action ( 67 FR 44713), we used the HCl RfC to determine the long term health effects of chlorine emissions, since chlorine photolyzes very quickly to HCl in sunlight. Two commenters ( IV D 03, IV D 05) supported this methodology and stated that our decision was based on sound scientific knowledge of the pollutants of concern.

In contrast, two other commenters ( IV D 06, IV D 07) did not agree with our 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).

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 to validate our original assumption.

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, reactions with oxygen atoms, and reactions with water vapor. Each pathway results in different amounts of Cl 2 being removed from the 20 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 HCl 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. In order to provide an upper bound estimate of the chronic risks to compare with the lower bound estimates assuming that all chlorine was converted to HCl, we conducted modeling assuming that no chlorine is photolyzed.

In general, we consider an exposure concentration which is below the RfC concentration ( what we call a hazard quotient of 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).

As discussed above, we conducted additional modeling for major source 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 HCl. The hazard quotients resulting from this additional modeling defined the upper bound of our risk assessment.

The highest upper bound hazard quotient estimated by the model is just over 0.3. ( For more details regarding this revised risk assessment, refer to table 2 of the responses to comment document, available in the docket.) 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 HCl 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, that none of the major sources included in this 21 subcategory will have emissions of chlorine or HCl that exceed a level of exposure which is adequate to protect public health and the environment with an ample margin of safety.

Comment: Two commenters ( IV D 06, IV D 07) did not support EPA's use of the AEGL2 for use as a short term exposure limit for chlorine and HCl. One commenter ( IV 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 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. Another 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 recommended that EPA use the American Conference of Governmental Industrial Hygienists ( ACGIH), which has a 1 hour Short Term Exposure Limit ( STEL) similar to the AEGL1 value of 1 part per million ( ppm), for chlorine, and is used to protect against eye and mucous membrane irritation. The commenter stressed 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, l hour, 4 hours, and 8 hrs.

As utilized in the proposed action, the AEGL2 1 hour concentrations for chlorine and HCl are 5,800

g/ m3 and 33,000

g/ m3, respectively.

The 1 hour AEGL1 concentration for chlorine is 2,900

g/ m3 and the corresponding value for HCl is 2,700

g/ m3. The ACGIH short term exposure limit ( STEL) for chlorine, which is 1 ppm is approximately equal to the AEGL1 value of 2,900

g/ m3.

Although we stand by our original analysis, which used the AEGL2 level, we have incorporated 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 22 compared the short term ( 1 hour average) modeling results from the original acute 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.

The maximum modeled 1 hour chlorine concentration for two of the three plants with the mercury cell chlor alkali process is less than 5 percent of the AEGL 1 ( and ACGIH) value for chlorine. Further, the highest modeled concentration for any plant, 155

g/ m3, is less than 6 percent of the AEGL1 values. The highest modeled 1 hour HCl concentration for any plant,

32

g/ m3, is less than 2 percent of the AEGL1 value for HCl. Furthermore, all of the mercury cell chlor alkali facilities also produce chlorine using a non mercury chlorine production process ( i. e.,

diaphragm cells). The modeled emissions represent chlorine and HCl emissions from both processes. Therefore, the chlorine and HCl emissions from the mercury cell chlor alkali process would be even lower.

Based on this comparison, we conclude that the chlorine and HCl emissions from mercury cell chlor alkali production plants do not represent an unsafe level of acute exposure. We further maintain that, along with the chlorine exposure assessment, this proves that an ample margin of safety is provided with no additional control.

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 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 ( IV D 03, IV D 05) stated that the 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 the conservative assumptions made in the health effects assessment, emissions estimates, and exposure assessment were appropriate for the proposed action.

In contrast, one commenter ( IV D 07) stated that the risk assessment fell short of the Agency's prior practice. According to the commenter, whenever EPA has made determinations 23 to regulate a specific pollutant based on health considerations ( e. g., national ambient air quality standards ( NAAQS) for ozone and 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 the commenter IV D 07' 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." As discussed elsewhere in this preamble, we maintain that the RfC and AEGL values used as benchmarks for this assessment are scientifically sound and appropriate. The emissions data and 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 major sources in the subcategory. We have established hazard indices for chlorine and HCl for each major 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 reassessments. We will base each risk assessment for this and future regulatory action on sound scientific principles.

Comment: In the proposed action, the risk assessment modeling was conducted by placing receptors at the geographic 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.

Two commenters ( IV D 06, IV D 07) did not agree with this 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 ( IV 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 24 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 ( IV 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 noncancer ( 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. They 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).

Response: We certainly agree with the commenters that the greatest impacts will likely occur near the facility for this source subcategory. However, we do not agree with the commenters that our approach fails to meet statutory requirements. 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, 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 section 112( d)( 4).

Comment: One commenter ( IV D 06) stated that all chlorine emissions from chlorine production facilities that are collocated with other source categories need to be reviewed as a 25 whole when evaluating public health risk, adverse environmental effects, and possible control strategies. The commenter stressed that other sources of chlorine and HCl should be included in the risk assessment under section 112( d)( 4). The commenter was concerned that not accounting for all chlorine and HCl 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 section 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 HCl 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 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 mercury cell chlor alkali facilities are collocated with other source categories. However, based on the risk assessment for chlorine and HCl emissions from mercury cell chlor alkali plants, the predicted impacts from chlorine and HCl at these plants are extremely low. We believe that the human health and environmental impacts from all sources in the subcategory even when collocated with other chlorine and HCl 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 action, most major processes at the sites where mercury cell chlor alkali 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 be inappropriate to include emissions from those sources in an assessment for the mercury cell chloralkali subcategory conducted under the authority of section 112( d)( 4).

Comment: Two commenters ( IV D 06, IV D 07) stated that the environmental effects analysis was not adequate. One commenter ( IV D 06) stated that potential ecological effects of 26 HCl emissions have not been properly referenced. One commenter ( IV 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 in 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." 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 section 112( d)( 4) did not have any adverse environmental effects, the Agency did not properly consider the issue. Therefore, the commenter stated that EPA could not promulgate standards under 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. The level of our analysis at proposal was adequate to satisfy the requirements of section 112( d)( 4).

The commenters did not suggest that they believed there was the potential for adverse environmental effects from HCl or chlorine emissions from mercury cell chlor alkali 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 in the proposal preamble, we did not perform a separate evaluation of chronic chlorine exposure because chlorine is converted to HCl in the atmosphere so rapidly.

Atmospheric exposure is the primary pathway for environmental effects from chlorine emissions. However, since most chlorine is converted to HCl, studies have focused on the effects of HCl on vegetation. Although plant exposures to elevated levels of chlorine can cause plant injury, it tends 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, decreased levels of chlorphyll a and b, decreased leaf areas, obvious chlorosis, and a decline in fruit production due to chlorine emissions. 27 There is evidence of effects to animals due to accidental and/ or catastophic exposures, but the chlorine concentrations of these exposures are unknown. However, there are no data on exposure to historic or atmospheric concentrations.

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 a significant decrease in phytoplankton activity following exposure to 0.1 ppm chlorine in cooling tower water. Additional laboratory studies showed that continuous exposure to 0.002 milligrams per liter ( mg/ L) total residual chlorine ( 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, shoot length, and chlorophyll content.

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 lethal concentration 50% ( LC 50) 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. 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 50 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.

Acute and chronic exposures to predicted chlorine and HCl concentrations around the sources are not expected to result in adverse toxicity effects. These pollutants are not persistent in the environment. The chlorine and HCl emitted should not significantly contribute to aquatic 28 chlorine concentrations and are not likely to accumulate in the soil. Chlorine rapidly converts to HCl in the atmosphere, and chlorine and HCl are not believed to result in biomagnification or bioaccumulation in the environment. Therefore, we do not feel there will be adverse ecological effects due to chlorine and HCl emissions from mercury cell chlor alkali plants.

2.3 COMPLIANCE DATE Comment: Three commenters ( IV D 04, IV D 05, IV D 07) requested an extension of the compliance date, which EPA proposed to be 2 years from the effective date of the final rule.

Commenters IV D 04 and IV D 07 recommended that the compliance date should be changed to 3 years after promulgation. The commenters stated that affected facilities are being required to install costly, complex control and monitoring equipment, as well as establish additional operating and maintenance procedures at their facilities in order to ensure compliance with the emission limitations and work practice requirements of the proposed rule. The commenters believed that 2 years was not a sufficient period of time to complete such tasks, specifically the continuous monitoring requirements. The commenter further argued that other MACT standards, most notably the Hazardous Organic NESHAP ( HON) and the Hazardous Waste Combustor MACT standard, included a three year compliance schedule, and that this time period was more appropriate for the proposed standard as well.

Commenter IV D 05 argued that EPA should extend the compliance date to allow facilities to manage the high costs of installing the control methods required by the NESHAP.

Response: We agree that since the existing sources are required to install complex monitoring equipment and to establish additional operating and maintenance procedures, it is reasonable to allow more time than the proposed 2 year compliance period. Section 63.6( c)( 1) of the NESHAP General Provisions states that ". . . in no case will the compliance date . . . exceed 3 years after the effective date of . . .." Therefore, the final rule specifies that the compliance date for existing sources is 3 years after the effective date of the final rule. [ The compliance date for new and reconstructed sources is the effective date of the final rule. EPA does not expect,

however that any new mercury cell chlorine production plants have been or will be constructed since the proposed rule was issued.]

2.4 EMISSION LIMITATIONS 29 Comment: Two commenters ( IV D 06, IV G 01) were concerned about subcategories that impacted the emission limitations, although these concerns were on different levels.

Commenter IV D 06 commented on the establishment of different emission limitations for similar emission point types, while commenter IV G 01 ( which submitted comments after the close of the comment period) expressed concerns about the subcategorization of mercury cell chlor alkali plants from other types of chlor alkali plants.

Commenter IV D 06 recommended that EPA reconsider the subcategories and avoid creating too many small subcategories. The commenter argued that although the Act allows EPA to distinguish among classes, types and sizes of sources, the proposed rule's subcategorization disaggregated the chlorine source category too much. The commenter also maintained that the proposed subcategorization scheme undermines an intent of CAA section 112 of reducing HAP emissions. The commenter was particularly concerned with the subcategories that contained less than five sources ( e. g., plants without end box ventilation systems, plants with oven type thermal recovery units, and plants with non oven type thermal recovery units).

The commenter further argued that for plants with and without end box ventilation systems, eliminating end box ventilation systems is " technically feasible." According to the commenter, some plants currently operate without end box ventilation systems, and plants with end box ventilation systems could replace them with equipment that does not require end box ventilation systems. According to the commenter, EPA's justification for making the distinction between plants with and without end box ventilation systems appeared to be based on the costs associated with changing a plant's equipment. The commenter maintained that the Act does not authorize EPA to consider costs when developing subcategories ( and may consider costs only later, when deciding whether to establish standards beyond the MACT floor). Therefore, the commenter concluded that EPA had considered costs out of order and undermined the minimum stringency requirements of the Act.

Commenter IV G 01 recommended that EPA redefine MACT to ban the use of mercury cell technology. The commenter explained that this would be easily achievable because the majority of the chlorine production industry already uses other, superior technologies such as membrane cells and diaphragm cells. The commenter claimed that EPA abused its authority to establish subcategories of emission sources by creating a subcategory of " mercury cell chlor alkali 30 plants" within the chlorine production source category which limits the pool of facilities upon which the MACT floor is based to those who create dangerous pollution, as opposed to those industry leaders that use non polluting and readily available equipment.

The commenter further listed a lack of confidence that the mercury cell process could be adequately controlled. The commenter explained that the work practice requirements which are proposed to address fugitive emissions, the largest of emissions from this process are too weak.

Finally, he commenter stated that converting all mercury cell plants to membrane cells would still be cost effective, and that their estimate of the cost to convert all mercury cell plants to other technologies ($ 920 million) was justifiable given the significant threat to public health and the environment posed by mercury.

Response: Although there are some facilities that operate sealed end boxes without endbox ventilation systems, we do not agree with the commenter that it would be technically feasible for facilities that use open end boxes to convert to a closed end box system. According to the industry, the two existing facilities that operate without end box ventilation systems had sealed end boxes incorporated into the original design of the cell, which resulted in no need for ventilation systems. We did not consider costs when making this decision, but based our decision on cell design and emission profile ( facilities that do not have end boxes have inherently lower emissions than those with end boxes due to the absence of that emission point) when establishing MACT for mercury cells. Therefore, we believe that it was appropriate to establish MACT for mercury cells with closed end box systems despite the fact that there are only two facilities with this type of system.

For facilities with mercury recovery processes, we identified two different technologies for mercury thermal recovery units: oven type and non oven type units. Oven type units are batch ovens that heat mercury wastes to a temperature of about 1,000oF for 24 to 48 hours, depending on the type of waste. Non oven type units are rotary kilns into which mercury wastes are fed at regular intervals ( usually about every 5 minutes) and fired at a temperatures of approximately 1,300oF, with a residence time of about 3 hours. In addition to differences related to operating temperature and residence time, there are significant differences in the volumetric flowrates produced by the oven and non oven units. The volumetric flowrate from an oven type unit is more than an order of magnitude lower than that of an non oven type unit. The differences 31 between these two types of units have an impact on mercury concentration and mass flow rate, as well as factors that affect mercury loading to the recovery system. Based on these technical and operational differences between the types of mercury thermal recovery units, and their potential effect on emissions characteristics and control device applicability, we believe that it was appropriate to distinguish between oven type and non oven type recovery units for the purpose of establishing MACT for mercury recovery plants.

We wish to point out that in all cases the proposed standards are at beyond the floor levels. We believe that the commenter's ( IV D 06) primary concern is that source categories with small numbers of sources leads to establishing standards that do not achieve emission reductions beyond the status quo. When standards are set at beyond the floor levels, this concern is addressed.

Finally, we disagree with the commenter ( IV G 01) that we abused our authority to create subcategories by subcategorizing the chlorine production industry and only including mercury cell plants in the MACT floor analysis. It is our general policy to subcategorize when there are technical distinctions among classes, types, or sizes of sources, and manufacturing processes of sources, that would impact setting an appropriate emission limit even when creating the subcategories leads to some with a small number of sources. This policy is supported by the broad discretion provided to the Agency to establish subcategories under CAA section 112( c),

the legislative history, and EPA's prior rulemakings. In the House Debate on H. R. 3030,

Congressman Bliley discussed the need to allow EPA to create subcategories of sources under section 112:

Furthermore, it is apparent that if the title III MACT requirements are to work sensibly, it is important that the appropriate control measure be employed in light of the nature of the facility to be regulated. Some industries have processes that are central to given subcategories of the industry. In my view, the other body employed the proper approach and degree of flexibility wherein it recognized . . . that " The Administrator may consider the type of process employed in making decisions on subcategories and standards." Of course, there is nothing in the language of H. R. 3030 that would prevent such an interpretation. Indeed such an interpretation and use of subcategorization is vital to prevent the cost ineffective application of a MACT which is inappropriate to the kind of process that is integral to a source.

House Debate ( May 23, 1990), reprinted in A Legislative History of the Clean Air Act Amendments of 1990, Comm. Print S. Prt. 103 38 ( 1993) (" Legis. Hist.") at 2725. The senate 32 debate over the conference bill echoes this notion that EPA should use subcategorization to ensure that the technology based MACT standards are " appropriate" for the particular process or technology used at a source. See Senate Debate ( Oct. 27, 1990), reprinted in Legis. Hist. at 1029 ( Sen. Baucus explaining, "[ T] he bill directs the EPA to list categories and subcategories for these major sources so that MACT is appropriately applied."). In contrast to what commenters have asked for ( the closure of mercury cell chlor alkali sources), Congress specified that " MACT is not intended . . . to drive sources to the brink of shutdown." 2 Legis. Hist., at 3352.

In general, EPA has previously taken the position that subcategorization is appropriate where types of emissions and/ or type of operation make use of the same air pollution control technology infeasible. The Agency's rulemakings reflect this general understanding and provide criteria for subcategorization that focus on the appropriateness of applying similar technologybased requirements at different sources. The EPA has explained:

In general, we make the decision to establish subcategories within a source category as part of the process of developing a MACT standard applicable to that category. In establishing subcategories, we typically consider factors such as process operations, emission characteristics, control device applicability, and opportunities for pollution prevention.

( 64 FR 56493, 56495, Oct. 20, 1999, " Notice of Complete Petition for Two Piece Can Subcategory Delisting.")

The criteria EPA has described for establishing subcategories all relate to the ability of different sources to apply similar controls. More recently, in December 2000, EPA noted:

In developing standards under section 112( d) to date, the EPA has based subcategorization on considerations such as: the size of a facility; the type of fuel used at the facility; and the plant type. The EPA also may consider other relevant factors such as geographic conditions in establishing subcategories.

( 65 FR 79825, 79830, Dec. 20, 2000, " Regulatory Finding on the Emissions of Hazardous Air Pollutants From Electric Utility Steam Generating Units"; see also 64 FR 56494, " In establishing subcategories, EPA considers factors such as process operations ( type of process, raw materials,

chemistry/ formulation data, associated equipment, and final products); emission characteristics ( amount and type of HAP); control device applicability; and opportunities for pollution prevention. The EPA may also look at existing regulations or guidance from States and other regulatory agencies in determining subcategories.") 33 We feel that the subcategorization scheme it has used for this category of sources ( as described above and in the proposed rule) is consistent with the statute, the legislative history, and EPA's past implementation of section 112( c) and the MACT program. The HAP emitted by the two subcategories ( mercury cell chlor alkali plants and non mercury cell chlorine production)

plants are different    while plants in both categories emit chlorine and HCl, only plants in the mercury cell subcategory emit mercury. The processes used to produce chlorine that the plants in the two subcategories used are generally different ( because of the use of the mercury cells). Thus,

no change was made in response to this comment and the final rule does not ban mercury cells ( except the final rule does prohibit the emission of mercury from new sources).

With regard to the cost effectiveness of a ban of mercury cell chlor alkali facilities, the commenter did not provide any basis for their estimate so we could not verify these costs.

Further, we do not feel that " conversion" accurately describes the replacement of a mercury cell plant to another technology. There is little salvageable from a mercury cell plant that can be used in the construction of a membrane cell plant, so the demolition of the mercury cell plant followed by the construction of a membrane cell plant is a more accurate characterization.

Therefore, we did not promulgate a final rule that requires non mercury technology for chlorine production.

Comment: A commenter that submitted comments after the close of the comment period ( IV G 01) urged the EPA to ban the use of thermal recovery units since they emit mercury and there exist alternative, non thermal technologies for recovering mercury from wastes which have no mercury emissions.

Response: As explained in the preamble for the proposed rule, ( 67 FR 44689), we considered requiring non thermal technology for new sources. However, unlike thermal recovery units which are capable of treating a variety of waste types, the chemical recovery and the purification still processes have limited application. Both are suitable to treating only certain waste types, K106 wastes for the former and end box residues for the latter. Plants using these nonthermal recovery processes transfer their remaining wastes off site for treatment, which typically involves thermal recovery. Given this limitation, we concluded that these nonthermal recovery processes did not qualify as a suitable basis for new source MACT. This same rationale 34 explains why we reject the commenter's suggestion to require non thermal technology for existing sources.

Comment: One commenter ( IV D 06) stated that the proposed rule violates the CAA because the Agency did not establish standards for some parts of chlor alkali plants that emit mercury. The commenter noted that under the proposed rule, EPA defined two affected sources:

mercury cell chlor alkali production facilities and mercury recovery facilities. The commenter did not agree with EPA's determination that within mercury cell chlor alkali production facilities,

chlorine purification, brine preparation and wastewater treatment operations should not be subject to emission standards because they have low mercury air emissions. Similarly, the commenter did not agree with the EPA's decision not to regulate chemical mercury recovery and recovery in batch purification stills at mercury recovery facilities. According to the commenter, the CAA does not allow the Agency to exempt certain classes, types and sizes of sources from emission standards, unless EPA finds no potential for emissions. Therefore, the commenter stated that EPA had a legal obligation to establish standards that cover all mercury emitting parts of chloralkali facilities, and the Agency must re visit and set emission standards for the parts of the production and recovery facilities with low mercury emissions.

Another commenter ( IV G 01), which submitted commenters after the close of the comment period, urged EPA to set limits on or eliminate mercury contamination in caustic so that caustic purchasers will not be additional sources of mercury emissions.

Response: During development of the proposed rule, we did not receive any data to indicate that mercury was emitted from chlorine purification, brine preparation, product caustic,

or wastewater treatment operations, and our knowledge of the process indicated that any potential emissions would be very limited ( 67 FR 44674). Furthermore, we did not receive any data indicating that control measures designed to reduce HAP were in use at existing facilities that had these units. The same holds true for chemical mercury recovery and recovery in batch purification stills at mercury recovery facilities. Therefore, with no reported emissions and process evidence that any emissions would be very limited, we concluded that there was no potential for emissions. Adding to this the existence of a MACT floor of no control ( because none are controlled), we did not to regulate these processes. 35 The commenters did not provide emissions data that would indicate that these sources emit significant amounts of mercury, or emit mercury at all. Therefore, the final rule does not contain standards for mercury emissions from chlorine purification, brine preparation, wastewater treatment operations, product caustic, chemical mercury recovery and recovery in batch purification stills.

We point out that the final rule does contain very stringent emission limitations for all point sources that have been demonstrated to be sources of mercury emissions. Further, the work practice requirements in the final rule address fugitive mercury emissions in the chlorine purification, brine preparation, wastewater treatment areas, as well as areas where chemical mercury recovery processes and batch purification stills are located.

Comment: One commenter ( IV D 06) stated that when establishing MACT for the proposed subcategories, EPA should not rely on worst case data. The commenter indicated that it was not appropriate for EPA to have averaged the emission levels from all sources in each source category. According to the commenter, one court did approve the practice of using " worst case" data, but its approval was in the context of source categories that had more than 30 sources. Thus, the risk of " formalizing the status quo" was lower and the technique was more reasonable.

The commenter stated that given the risk of formalizing the status quo emission levels when subcategories with very few source occur, EPA should reconsider alternatives for beyond

thefloor standards. The commenter stated that more stringent beyond the floor standards are more consistent with the CAA's purpose of reducing emissions.

Response: We are unclear what the commenter means by relying on " worst case" data, as the commenter did not refer to a specific emission unit or data set. In two cases we did use the highest values from given data sets and perhaps this was considered using worst case data by the commenter. In setting an outlet concentration standard for mercury thermal recovery units ( 67 FR 44687 and 44688), we evaluated data sets and established representative outlet concentration values by averaging the highest values from those data sets. As stated in the proposal preamble ( 67 FR 44687, section III. D. 3), we evaluated several options for how to use the provided data to establish a numerical emission limit ( i. e., outlet concentration). In order to account for variability in outlet mercury concentrations due to processing different wastes, normal variation in 36 recovery/ control equipment performance, and to account for our inability to correlate waste type processed to emissions, we chose to use the highest values from individual data sets to establish a numerical emission limit. We believe that it was appropriate to utilize these values to represent the level of control achieved by the best controlled plant. Selection of a lower concentration would result in this best controlled plant being out of compliance at times. For instance, if we had selected the median concentration, the plant would be out of compliance half the time.

The commenter did not provide any specific and/ or technical information to lead us to reconsider our initial decisions. Therefore, no change will be made in response to this comment.

The commenter expressed concern that using worst case data risks formalizing the status quo emission level. It should be noted that in both cases the standard was set at a beyond

thefloor level. For oven type mercury thermal recovery units, the decision to set standards beyondthe floor will result in lower emission levels at two out of three plants using oven type units. For non oven type units, the decision to set standards beyond the floor will result in lower emission levels at two out of three plants. Therefore, we do not believe the standards set for mercury thermal recovery units have formalized the status quo emission level.

Furthermore, section 112( d)( 1) of the Act allows us to distinguish among classes, types,

and sizes of sources when establishing the standards for a particular source category, without specifying a minimum number of sources to be considered in establishing the MACT floor.

Therefore, we believe that it was appropriate to establish MACT for the identified subcategories regardless of the number of facilities within the subcategory. No change was made in response to this comment.

Comment: Commenter IV D 06 stated that the EPA's exclusion of data from one of the plants using non oven type mercury thermal recovery units was arbitrary and capricious.

According to the commenter, EPA excluded data from one plant with a rotary kiln because the data were unreliable, because the company took a cautious approach, and because the data were significantly lower than data submitted by other plants. The commenter maintained that EPA needed to offer better reasoning to support and establish that the data are unreliable.

Response: During the development of the emissions limit for non oven type mercury thermal recovery units, we evaluated the mercury recovery/ control systems operated at three facilities. Data from one facility ( PPG, Lake Charles, LA) was based on a company developed 1Memorandum, from Bhatia, K., EC/ R Incorporated, to Rosario, I., EPA/ OAQPS/ ESD// MG. June 27, 2001. Attachment B. Summary of Information on Mercury Thermal Recovery Unit at PPG's Lake Charles, Louisiana Plant. EPA Air Docket A 2000 02, Number II B 17.

37 procedure derived from an Occupational Safety and Health Administration ( OSHA) method for determining worker exposure. The average measured mercury concentration for the PPG facility was an order of magnitude lower than averages from the other two facilities, and the minimum measured value was two orders of magnitude lower than the minimum values for the other two facilities. In determining which data to use to develop the MACT floor, we concluded that the data from the PPG facility underestimated emissions and thus overstated the performance of the mercury recovery/ control system. Therefore, we rejected this data to determine the MACT floor.

The commenter has not provided technical meritous arguments ( e. g., comments on the OSHA procedures or comments on the relative magnitude of the rejected data compared to other data) that would lead us to reconsider our decision to not use the data in question. Furthermore,

we utilized a statistical test ( i. e., Rosner's Test) to determine that the data points were outliers.

Therefore, we are not making any changes to our original decision.

However, we would like to reiterate why we did not use these data because we believe the commenter has slightly mischaracterized our rationale. Specifically, the commenter stated that we rejected the data because the company used a cautious approach. We do not want that statement to be interpreted by the public to mean that we rejected the data because conservative procedures were used because that is not the case. The company providing the data cautioned us that the procedures used provide credible information on relative changes in performance, but they do not necessarily produce accurate information on actual mercury releases. Personnel from our Emission Measurement Center ( EMC) reviewed the method and concluded that "... it should not be considered to be a quantitative procedure that can measure absolute mercury emissions for inventory purposes." 1 In light of these statements and our observations that the data were uncharacteristically low with no apparent performance related reasons for the low values, we decided to not use the data.

Comment: Two commenters ( IV D 04, IV D 07) did not agree with the proposed " beyond the floor" limitations. They stated that there is no justification for EPA to set emission 2 Hazardous Air Pollutant Emissions from Mercury Cell Chlor Alkali Plants  Background Information for Proposed Standards. EPA 453/ R 02 007. U. S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, North Carolina. February 2002. Chapter 6. [ Air Docket A 2000 32 Item Number II A 02]

3 Memorandum. Bhatia, K., EC/ R Incorporated, to Rosario, I., U. S. Environmental Protection Agency. Impacts Calculations for Mercury Cell Chlor Alkali Plant NESHAP Regulatory Alternatives. December 14, 2001. [ Air Docket A 2000 32 Item Number II B 24]

4U. S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Emissions Standards Division. OAQPS Control Cost Manual, Fifth Edition ( EPA 453/ B 96 001). Chapter 4. February 1996.

38 limits beyond the floor, as proposed. The commenters stressed that EPA is required to assess the cost benefit relationship when considering " beyond the MACT floor" limitations. According to the commenters, the Agency has not set forth an accurate basis for costs associated with meeting the MACT floor or cost/ benefits associated with meeting the " beyond the MACT floor" emission limitations.

Another commenter ( IV G 1), which submitted comments after the close of the comment period, strongly endorsed EPA's determination that beyond the floor control is merited for this industry sector.

Response: We disagree with the first two commenters' assertions that we did not have a justification for going beyond the floor, and that we did not have an accurate basis for costs associated with meeting the MACT floor or meeting beyond the floor emission limitations. We conducted a very detailed plant specific cost impacts analysis2,3 based on information and procedures contained in the EPA OAQPS Control Cost Manual4 and vendor quotations. All of this information was available in the docket. However, the commenter did not provide any specific comments on this detailed analysis or any specific data or rationale to refute our cost analysis. Therefore, we stand by our original analysis and have not made any changes to the cost impacts approach. Based on our analysis, we concluded that the costs/ benefits of going beyond the floor are warranted. Given the persistent nature of mercury in the environment and its associated health and welfare impacts, we continue to believe that the additional emission reductions that will be achieved by the beyond the floor option are warranted considering the associated costs. 39 Comment: Two commenters ( IV D 04, IV D 07) were concerned with the proposed mercury emission limitation, which has a daily averaging period. According to the commenters,

the Agency developed the proposed standard using annual average emissions and actual annual production and then interpolated to a daily limit without regard to statistical error.

Therefore, the commenters requested an annual average emission rate limit. The commenters proposed adding together the previous 365 days emission totals and dividing by the annual production capacity. This annual emission rate would then be compared to the MACT limitation. The commenters maintained that this approach would be more consistent with the data used to develop the MACT standard and would result in the emission reductions MACT is designed to achieve. The commenters stated that their proposed averaging period would require facilities to react proactively to forestall statistically significant increases in emissions, without having to respond to natural variations in data.

As an alternative to the annual averaging period, the commenters stated that if single value daily limits are established, they should be set at not less than two times the annual limit divided by 365 ( days). To support the use of a variability factor, the commenters provided three arguments. First, the proposed limits were based on annual chlorine production capacity.

Second, the commenters were concerned about how to address the daily limits during days when the plant is not producing chlorine. The commenters maintained that mercury is still emitted from facilities that are temporarily not producing chlorine. Finally, the commenters stated that the limited data set used to develop the proposed limit does not reflect variability associated with dayto day operation, including variability in performance of control devices and monitoring systems.

The commenters reasoned that for a commonly used default coefficient of variation ( CV) of 0.6,

even with ten representative samples, the multiplier is 3.0 ( the commenters referred to the TSD for Water Quality Based Toxics Control, EPA/ 505/ 2 90 001). Therefore, using a multiplier of 2.0 is more than protective when setting emission limitations that must be met every day. The commenters recommended that EPA should subject this limited data set to a statistical method of characterizing the 99th percent confidence level that the data will fall below a stated value.

Response: While not stated, we assume that the commenters are referring to the proposed by product hydrogen/ end box ventilation limit. The commenters are correct in that the normalized mercury emissions used to establish the standards were based on annual average 40 emissions and annual actual chlorine production. Therefore, the commenters' concerns about the variability of the control systems and the ability to comply on a daily basis with this limit have merit. We considered the two options offered by the commenters ( 365 day compliance period and adjustments to account for daily variations).

We do not believe that it would be appropriate to apply a generic multiplier from other industries to the limit for mercury cell chlor alkali plants. In addition, mercury cell data were not available to assess the variability in emissions from these emission points. Therefore, we concluded that the emission limitation should reflect an annual average. This would be consistent with the data used to create the emission limitation and would allow for short term variations in operations and control device performance.

The final rule is allowing weekly monitoring/ testing as an alternative method to determine continuous compliance with the emission limitations. This is discussed in more detail in section 2.7 of this document. Therefore, in order to be consistent with this continuous compliance approach, we concluded that the by product hydrogen/ end box ventilation emission limitation final rule should be annualized on a 52 week rolling basis. Specifically, the final rule requires that mercury emissions from all by product hydrogen streams and end box ventilation system vents not exceed 0.076 grams Hg/ Mg Cl 2 for any consecutive 52 week period.

We do not believe the concerns raised by commenters apply to the proposed emission limitation for mercury thermal recovery unit vents which were based on short term performance tests or periodic sampling. Therefore, no changes were made to the limit for mercury thermal recovery unit vents in response to this comment.

Comment: Two commenters ( IV D 04, IV D 07) were concerned that the very low emission limits required by EPA's beyond the floor determination cannot be obtained by the industry as a whole. Specifically, the commenters stated that the Agency lacks high quality point source emission data upon which to base their " beyond the floor" limits. According to the commenters, the mercury emission limitations for hydrogen vent gas streams are based on the limited data provided by a single facility in Maine that has been closed for nearly 2 years. The commenters maintained that for all of the eleven plants combined ( ten affected plants plus the closed Maine plant), there was very little high quality point source emission data. Due to the significant chance that the data used to develop the standard are biased and quantitatively non 41 representative, the commenters stated that the Agency was not justified in moving beyond the floor to the most stringent value ever obtained by the industry.

The commenters further argued that EPA's conclusion that the " beyond the floor" emission limitations can be met with existing, commercially available control equipment is not supported and thereby seriously flawed. The commenters pointed out that EPA presented no data in the preamble or elsewhere in support of their decision that the proposed standards could be met with commercially available control systems.

Response: First, we disagree with the commenters' assertions that we did not have justification for going beyond the floor, and that we did not have an accurate basis for costs associated with meeting the MACT floor or meeting beyond the floor emission limitations. We conducted a very detailed plant specific cost impacts analysis which is available in the docket.

The commenters did not provide any specific comments on this detailed analysis or any specific data or rationale to refute our cost analysis. Therefore, we stand by our original analysis and have not made any changes to the cost impacts approach. Based on our analysis, we concluded that the costs/ benefits of going beyond the floor are warranted. Given the persistent nature of mercury in the environment and its associated health and welfare impacts, we continue to feel that the additional emission reductions that will be achieved by the beyond the floor option are warranted considering the associated costs.

In the proposal preamble ( 67 FR 44682) we acknowledged that there was uncertainty associated with the level of control associated with the beyond the floor option proposed because the molecular sieve adsorption control technology is no longer commercially available and because the plant representing this level of control is no longer operating. We did not receive any comments indicating that the molecular sieve control technology is commercially available.

Further, since the plant has closed we were unable to obtain additional information to further scrutinize the data to ensure that it was not biased and quantitatively non representative.

Therefore, we have concluded that we cannot fully demonstrate that the proposed beyond

thefloor standard is achievable using commercially available technology.

However, in the proposal preamble ( 67 FR 44682), we acknowledged that there was uncertainty associated with the level of control associated with the level of control associated with the beyond the floor option proposed because the molecular sieve adsorption control technology 5 Memorandum. Bhatia, K., EC/ R Incorporated, to Rosario, I., U. S. Environmental Protection Agency. Background on Vent Control System Enhancements to Meet Regulatory Alternatives for Existing Mercury Emission Sources at Mercury Cell Chlor Alkali Plants. September 26, 2001. [ Air Docket A 2000 32 Item Number II B 22]

42 is no longer commercially available, and because the plant representing this level of control is no longer operating. We did not receive any comments indicating that the molecular sieve control technology is commercially available. Further, since the plant has closed we were unable to obtain additional information to further scrutinize the data to ensure that they were not biased and quantitatively non representative. Therefore, we have concluded that we cannot fully demonstrate that the proposed beyond the floor standard is achievable using commercially available technology.

In the proposal preamble, we also stated that we were retaining the option of setting the standard at the next lowest normalized emission value of 0.076 grams Hg/ Mg Cl 2 for plants with end box ventilation systems. The plant with this emissions level controls its by product hydrogen system with a series of iodine and potassium iodide impregnated carbon adsorbers, and their endbox ventilation system vent with a condenser and demister. These are commercially available technologies. Further, in the documentation for the proposed standard, we determined on a plantspecific basis which commercially available technologies could be made to comply with the proposed standard. 5 The commenters provided no comment on why the application of the very specific application of these technologies could not achieve the emission limitations.

The emissions estimates for the facility with normalized emissions of 0.076 grams Hg/ Mg Cl 2 are based on weekly testing using methods that are modifications of EPA Methods 101A and 102. The primary difference between the methods used by the facility and the EPA Reference Methods is that the sampling is not isokinetic. We discussed our opinion that data obtained using this type of modified method were acceptable to use in MACT standards in the proposal BID ( page 7 10). Therefore, it can be considered that the emission estimates used to establish the level of 0.076 g Hg/ Mg Cl 2 are based on weekly performance tests. We hardly consider such data to be of low quality. Therefore for the final rule, we have selected the 0.076 g Hg/ Mg Cl 2 beyond the floor option as MACT for plants with end box ventilation systems. 43 For the by product hydrogen stream for plants without end box ventilation systems and mercury thermal recovery unit vents, there were no questions raised regarding the availability of the control techniques used at the lowest emitting plants that formed the basis for the proposed emission limitations. Further, at proposal, we examined the data used to establish the emission limitations and determined that they were of adequate quality to be used to establish standards.

Therefore, the final rule retains the proposed emission limitations for these emission sources.

2.5 WORK PRACTICE STANDARDS 2.5.1 Format of Fugitive Standard Comment: One commenter ( IV D 06) recommended that EPA establish numerical standards for fugitive emissions. The commenter maintained that, absent published information on good mass balance analyses performed at chlor alkali facilities, one can only assume that significant mercury losses are occurring through fugitive emissions. Accordingly, the commenter felt it is crucial that the EPA step up efforts to address all potential release routes from such facilities, including fugitive emissions.

Another commenter ( IV G 01), which submitted comments after the close of the comment period, expressed the view that the mercury consumed cannot be accounted for in material balances. This commenter asserted that the proposed rule failed to address the majority of the true annual mercury emissions from the mercury cell chlor alkali industry. The commenter explained that the mercury used in this industry is not incorporated into final products or consumed in the process, so all mercury purchased is used to replenish mercury that has been lost from the manufacturing process. The commenter compared the amount of mercury purchased by the industry in 1994 ( 136 tons) to EPA's estimate of annual emissions ( 22, 200 pounds or 11.1 tons) and concluded that the proposed rule fails to account for nearly 90 percent of the true mercury emissions from this industry. The commenter drew this conclusion based on the assumption that most of the mercury would be released to the air rather than transferred off site as solid waste or accumulated in on site tanks and ponds. The commenter noted that EPA's estimate of annual emissions was based on outdated and inadequate estimates of fugitive emissions which were based on short term measurements taken when fugitive emissions were non representatively low. 44 Commenter IV D 06 recommended that EPA require both monitoring of fugitive emissions from cell rooms and waste storage areas and establish a reduction goal for such emissions.

According to the commenter, technologies are available to quantify airborne mercury concentrations continuously, and in combination with estimates of air flow rates, estimates of fugitive loss rates under selected conditions could be made and could serve as the basis for reduction targets.

Commenter IV G 01 urged the EPA to require each mercury cell chlor alkali facility to report their annual consumption of mercury as an indicator of total mercury loss. The commenter, which did not submit comments until after the end of the comment period,

acknowledged that the mercury could be released into the environment through other pathways ( e. g., solid waste) but stated that this would provide an upper bound estimate of annual mercury emissions. The commenter argued that this information would compensate for the current lack of data regarding fugitive emissions and encourage facilities to be more aggressive in their leak inspection programs once they realize the magnitude of the emissions.

Response: The commenter maintains that we should establish numerical standards for fugitive emissions based primarily on their assumption that significant emissions are occurring through fugitive emissions. This conclusion is reached because of the lack of good mass balance analyses, or as the second commenter points out, the inability of mercury cell chlor alkali plants to account for all the mercury consumed.

The issue of unaccounted for mercury has been the subject of intense scrutiny from other groups within EPA and the industry. As part of the Great Lakes Binational Toxics Strategy,

mercury cell chlorine producers report annually the total mercury consumption for the industry.

From the baseline consumption of 160 tons per year ( tpy) for the years 1990 1995, the industry reported an 81 percent reduction in 2001 ( 30 tpy). One of the commenters characterized the 2001 consumption as an outlier, but the 79 tpy consumed in 2000 still represents a significant decrease from the baseline level.

Even with this decrease in consumption, significant mercury remains unaccounted for by the industry. The mercury releases reported to the air, water, and solid wastes in the 2000 Toxics Release Inventory ( TRI) totaled around 14 tons. This leaves around 65 tons of consumed mercury that is not accounted for in the year 2000. 45 While it may appear to the commenters that the discrepancy in the mercury material balance is the result of fugitive emissions, there is little empirical evidence to support this conclusion. The commenters did not provide any emissions data to support their assertion. Industry claims that mercury which condenses and accumulates in pipes, tanks, and other plant equipment makes up a large component of the unaccounted for mercury. While the commenters completely discount this claim by the industry, it is relevant to consider the very high density of mercury. For instance, the 65 tons of unaccounted for mercury in 2000 averages just over 7 tons per plant. One gallon or mercury weighs around 113 pounds, meaning that around 124 gallons of mercury would be unaccounted for per plant. This is a very small percentage ( less than 2 percent) of the amount of mercury typically on site at most facilities. However, the industry is also unable to fully substantiate their theory. Therefore, the fate of all the mercury consumed at mercury cell chloralkali plants remains somewhat of an enigma.

We agree that work practice standards should only be set when it is not feasible to prescribe or enforce an emission standard. Indeed, our reasons for establishing work practices instead of numerical limits are based on factors associated with the practicality and feasibility of setting a realistic limit against which compliance can be measured and enforced.

First, data are not available to establish a numerical emission standard for fugitive emissions. As stated in the proposal preamble ( 67 FR 44680), emissions data for fugitives from cell rooms and waste storage areas are very limited to nonexistent. Second, we do not agree with the commenter's implication that available measurement technologies could support enforcing a numerical emission standard for the following reasons:

° mercury emission monitors have not been used to monitor fugitive emissions at mercury chlor alkali facilities for compliance demonstrations; ° the variability in the number of and location of exhaust vents at each facility affects the amount of air moved through the cell rooms and thus affects the mass emission rate of the fugitives; and ° the variability of the cell room roof configuration affects the feasibility of using the continuous emissions monitors at each facility.

Therefore, numerical emission limitations for fugitive emissions from the cell room and other areas is " not feasible," as defined in CAA section 112( h)( 2)( B). Thus, the final rule retains the work practice elements of the proposed rule. We have modified certain work practice standards,

as explained in another response. 46 However, in response to the concerns about unaccounted for mercury, we added a provision in the final rule that requires each facility to record and report the mass of mercury added to cells each year. In addition, we are requiring facilities to demonstrate initial compliance with this provision by providing their mass of mercury added to cells for the five years prior to the compliance date. This will establish a baseline for the mass of mercury being added to cells for each facility. Since the industry as a whole has been providing this data as a part of the Great Lakes Binational Toxics Strategy since 1996, we believe this data is readily available. While there are no mercury consumption reduction targets in the final rule, we believe that reporting the mass of mercury added to cells on a plant specific basis will encourage additional action to identify unaccounted for mercury and reduce mercury consumption.

Comment: A commenter that submitted comments well after the close of the comment period ( IV G 02) expressed the opinion that there was a fundamental flaw in the proposed rule because the proposal will weaken existing sources' obligations to limit mercury emissions from the cell room. They cited 42 U. S. C. § 7412( d)( 7), which prohibits emission standards from weakening existing standards. This commenter summarized the 40 CFR part 61 mercury NESHAP, which requires mercury cell chlor alkali plants to not emit more than 2,300 grams per day ( g/ day) of mercury from the entire facility, including the cell room, the by product hydrogen streams, the end box ventilation system vents, and other sources of mercury. The commenter stated that even if emissions from all other points were zero, emission from the cell room cannot exceed 2,300 g/ day. The commenter acknowledged that an owner or operator may forego cell room emission testing and assume that cell room emissions are 1,300 g/ day, but pointed out that complying with these work practices does not absolve the owner or operator of the obligation to meet the applicable numeric emission standard.

The commenter contrasted this with the proposed rule, which established numerical emission standards for by product hydrogen streams, end box ventilation systems, and mercury thermal recovery unit vents, but not for cell room fugitive emissions. The commenter claimed that emissions from the cell room will be able to exceed 2,300 g/ day so long as the work practices are followed, when the existing part 61 mercury NESHAP prohibits such a result.

The commenter concluded that it is not sufficient to say that the work practices that have been proposed are more stringent than the existing requirements, because neither the existing nor 47 proposed work practices by themselves require any given numeric level to be achieved. They argued that the existing numeric limit provides EPA and the public with an enforceable limit of performance to which owners and operators can be held. The commenter went on to indicate that such a numerical standard is particularly necessary, as plants are currently emitting far more than 2,300 g/ day of mercury. To support this assertion, the commenter provided information indicating that mercury cell plants add much more mercury to their cells than 2,300 g/ day, and they concluded that cell room emissions is a very likely way that mercury is lost. In conclusion,

the commenter stated that it would be inappropriate for EPA to rely entirely on a work practice standard and eliminate stricter provisions that would enable the Agency to insist that facilities keep their emissions below a set level.

Response: The commenter summarized the 40 CFR part 61 mercury NESHAP accurately,

with one exception. Paragraph § 61.53( c)( 1), which contains requirements for stack sampling to determine emission levels for cell room ventilation systems at mercury chlor alkali plants, states:

Stationary sources using mercury chlor alkali cells may test cell room emissions in accordance with paragraph ( c)( 2) of this section or demonstrate compliance with paragraph ( c)( 4) of this section and assume ventilation emissions of 1,300 grams per day of mercury.

Further, § 61.53( c)( 4) states:

An owner or operator may carry out approved design, maintenance, and housekeeping practices. A list of approved practices is provided in Appendix A of " Review of National Emission Standards for Mercury," EPA 450/ 3 84 014a, December 1984. Copies are available from EPA's Central Docket Section, Docket item number A 84 41, III B 1.

Therefore, if an owner or operator meets the prescribed work practice standards, they can assume a mercury emission rate from the cell room of 1,300 g/ day.

While the final rule does not retain the numerical emission limitation from the part 61 Mercury NESHAP, the requirements in the final rule for fugitive mercury emissions from the cell room are far more stringent than the design, maintenance, and housekeeping practices allowed by the Mercury NESHAP in lieu of meeting the numerical limit. In addition, the Mercury NESHAP contained only 18 work practice requirements as compared to the more than 80 design, operation,

maintenance, inspection, and required actions for repair contained in tables 1 through 4 to the final rule. The work practice standards specify the equipment and areas to be inspected along 48 with the frequency of the inspections and conditions that trigger corrective action. Response time intervals for when the corrective actions must occur are also specified. Furthermore, some types of inspections are required at more frequent intervals than required by the Mercury NESHAP ( e. g., inspecting decomposers for hydrogen leaks twice per day rather than once each day). In addition, the detailed recordkeeping procedures and reporting provisions are more fully developed than those in the Mercury NESHAP, as well as requirements for storage of mercury containing wastes.

Finally, the work practice standards contain a requirement for owners and operators to develop and implement a plan for the routine washdown of accessible surfaces in the cell room and other areas. The standards establish the duty for owners or operators to prepare and implement a written plan for washdowns and specify elements to be addressed in the plan. A requirement for washdowns is an important part of an overall approach to reducing cell room fugitive emissions.

Along with a floor level periodic mercury monitoring program ( discussed later), not only will the work practice standards in the final rule result in reduced mercury fugitive emissions ( and,

therefore, mercury consumption), but provide much more enforceable provisions so that an inspector can verify that they are being met.

In addition, we have calculated emission reductions for the final rule. Assuming that every facility is complying with the 1,000 g/ day limit from point sources ( this value assumes that 1,300 g/ day of the 2,300 g/ day facility limit are being used for fugitive emissions), we estimate that baseline emissions from all nine existing facilities ( relative to the Mercury NESHAP) are 3,285 kg/ yr. We estimate that annual emissions after the application of MACT to be 217 kg/ yr.

Therefore the final rule will result in emission reductions of 3,068 kg/ yr, or approximately 93 percent from the existing Mercury NESHAP. This supports our position that we are not setting a standard that allows backsliding. Therefore, once the final rule compliance date ensues,

sources subject to the provisions of the final rule will no longer be subject to the Mercury NESHAP.

Comment: Two commenters ( IV D 04, IV D 05) generally supported the proposed increase in inspections, documentation, and notifications, and the accelerated repair requirements.

However, one commenter ( IV D 05) recommended that EPA maintain the proposed rule's 49 standards for inspections and wash downs, but reduce the frequency and degree of recordkeeping mandated to document compliance.

Response: We thank the commenters for their support of the proposed work practice standards. However, without specific examples of requested changes or rationale for why Commenter IV D 05 finds the proposed recordkeeping requirements too detailed and onerous,

we are not led to reconsider the proposed requirements and no changes to these provisions have been made. In order to ensure that the work practices achieve emission reductions, we believe that it the recordkeeping provisions are appropriate.

2.5.2 Comments on Work Practice Tables Comment: One commenter ( IV D 07) stated that EPA should clarify Item 1. a of Table 1 ( Work Practice Standards  Design, Operation and Maintenance Requirements) to identify that it only applies to new construction or re construction of existing operations. The commenter recommended that EPA modify this item as follows:

" a. For new or reconstructed sources, Cconstruct each cell room interior using materials that are. . . "

Response: We agree with the commenter that there the language contained in Item 1. a of Table 1 ( Work Practice Standards  Design, Operation and Maintenance Requirements) is confusing. However, the language suggested by the commenter implies that this item applies to new or reconstructed affected sources, which are prohibited by the standard. Therefore, in order to address the commenter's concerns and to clarify Item 1. a of Table 1, we have made the following modification for the final rule:

a. For new or modified cell rooms, Cconstruct each cell room interior using materials that are...

By specifying that this item applies only to new or modified cell rooms, we are clarifying that this requirement does not apply to new or reconstructed affected sources.

Comment: One commenter ( IV D 07) stated that although the primary purpose of cell rooms is to house the mercury cells, frequently cell room buildings contain cell maintenance areas at one end. Therefore, the commenter was concerned that the maintenance part of the building that houses the cells would be considered part of the cell room. The commenter maintained that the wording of Item 1. d of Table 1 ( Work Practice Standards  Design, Operation and Maintenance Requirements) could be interpreted by an inspector to require all the maintenance 50 area activities to be relocated. The commenter recommended that Item 1. d be modified as follows:

" d. Minimize the number of items stored beneath the cells in each cell room.

Response: The purpose of this item is to ensure that items stored in cell rooms will not inhibit the cleanup of mercury spills and to prevent these items from becoming contaminated with mercury due to spills. We believe that keeping the area around and beneath the cells free of miscellaneous items will achieve this goal. Therefore, to address the commenter's concerns about portions of the cell room being used as maintenance areas, we have modified Item 1. d of Table 1 as follows:

d. Minimize the number of items stored around and beneath the cells in each cell room.

Comment: Two commenters ( IV D 04, IV D 07) suggested that EPA modify Item 2. b( 1)