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Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules
tkelley on DSKBCP9HB2PROD with PROPOSALS

Following promulgation of the 2003
Mercury Cell Chlor-Alkali Plants NESHAP, the EPA received a petition to reconsider several aspects of the rule from the Natural Resources Defense Council NRDC. NRDC also filed a petition for judicial review of the rule in the U.S. Court of Appeals for the District of Columbia Circuit. In a letter dated April 8, 2004, the EPA granted NRDCs petition for reconsideration and on July 20, 2004, the court placed the petition for judicial review in abeyance pending the EPAs action on reconsideration.
The EPA issued proposals on June 11, 2008 73 FR 33258, and on March 14, 2011 76 FR 13852, to respond to the reconsideration petition. We discuss the reconsideration and the 2008 and 2011
proposals further in section IV.A.2 of this preamble.
The use of mercury cell technology has been declining for decades due to conversions to non-mercury processes and closures. For example, in 1993, there were about 13 facilities in the U.S., and when we initiated the development of this RTR proposed rule in early 2020, there were two facilities operating. Since that time, one facility Ashta Chemicals in Ohio ceased operating the mercury cell process.3 So, now only one mercury cell chlor-alkali plant remains in operation. The one remaining mercury cell chlor-alkali facility is owned by Westlake Chemical operated by Eagle Natrium, LLC and is located in Marshall County, West Virginia. This is a large integrated chemical production facility whose products include chlorine and caustic from their chlor-alkali processes. In addition to the mercury cell process, chlorine and caustic are also produced in diagraghm cells at the site.
C. What data collection activities were conducted to support this action?
Data sources used for this effort include the 2017 National Emissions Inventory NEI, title V permit information, conversations with the West Virginia Department of Environmental Protection, and conversations with facility representatives. The NEI data were examined, and the processes and related emission sources associated with the mercury cell chlor-alkali plant were identified. In addition, information from data collection efforts from previous 3 Ashta Chemicals in Ashtabula, Ohio, has stopped operating the mercury cell process, and is on schedule to complete the conversion to membrane cells by end of 2020. Source: Personal communication, phone conversation: Between Brittany Johnson, Environmental Manager, Ashta Chemicals and Phil Norwood, SC&A, Contractor for U.S. EPA, December 4, 2020.

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regulatory efforts for the source category were consulted, including studies that were conducted for the 2002 proposals, the 2003 final actions, and the 2008 and 2011 proposals cited above.
D. What other relevant background information and data are available?
There are other sources that are often used by the EPA in obtaining information for RTRs. Examples include the EPAs Enforcement and Compliance History Online ECHO database, the Reasonably Available Control Technology/Best Available Control Technology/Lowest Achievable Emission Rate Clearinghouse, and NESHAP for similar industries.
However, these sources were not utilized for the review for the Mercury Cell Chlor-Alkali Plants NESHAP
because 1 the mercury cell processes are primarily sources of fugitive emissions and are unique such that control measures and work practices from other industries would not be applicable, and 2 since there is only one operating facility, it was more practical to focus on the specifics of that single facility.
III. Analytical Procedures and Decision-Making In this section, we describe the analyses performed to support the proposed decisions for the RTR and other issues addressed in this proposal.
A. How do we consider risk in our decision-making?
As discussed in section II.A of this preamble and in the Benzene NESHAP, in evaluating and developing standards under CAA section 112f2, we apply a two-step approach to determine whether or not risks are acceptable and to determine if the standards provide an ample margin of safety to protect public health. As explained in the Benzene NESHAP, the first step judgment on acceptability cannot be reduced to any single factor and, thus, the Administrator believes that the acceptability of risk under section 112 is best judged on the basis of a broad set of health risk measures and information. 54 FR at 38046.
Similarly, with regard to the ample margin of safety determination, the Agency again considers all of the health risk and other health information considered in the first step. Beyond that information, additional factors relating to the appropriate level of control will also be considered, including cost and economic impacts of controls, technological feasibility, uncertainties, and any other relevant factors. Id.

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The Benzene NESHAP approach provides flexibility regarding factors the EPA may consider in making determinations and how the EPA may weigh those factors for each source category. The EPA conducts a risk assessment that provides estimates of the MIR posed by emissions of HAP that are carcinogens from each source in the source category, the hazard index HI
for chronic exposures to HAP with the potential to cause noncancer health effects, and the hazard quotient HQ for acute exposures to HAP with the potential to cause noncancer health effects.4 The assessment also provides estimates of the distribution of cancer risk within the exposed populations, cancer incidence, and an evaluation of the potential for an adverse environmental effect. The scope of the EPAs risk analysis is consistent with the explanation in the EPAs response to comments on our policy under the Benzene NESHAP:
The policy chosen by the Administrator permits consideration of multiple measures of health risk. Not only can the MIR figure be considered, but also incidence, the presence of non-cancer health effects, and the uncertainties of the risk estimates. In this way, the effect on the most exposed individuals can be reviewed as well as the impact on the general public. These factors can then be weighed in each individual case.
This approach complies with the Vinyl Chloride mandate that the Administrator ascertain an acceptable level of risk to the public by employing his expertise to assess available data. It also complies with the Congressional intent behind the CAA, which did not exclude the use of any particular measure of public health risk from the EPAs consideration with respect to CAA section 112 regulations, and thereby implicitly permits consideration of any and all measures of health risk which the Administrator, in his judgment, believes are appropriate to determining what will protect the public health.

54 FR at 38057. Thus, the level of the MIR is only one factor to be weighed in determining acceptability of risk. The Benzene NESHAP explained that an MIR of approximately one in 10
thousand should ordinarily be the upper end of the range of acceptability. As risks increase above this benchmark, they become presumptively less acceptable under CAA section 112, and would be weighed with the other health risk measures and information in making an overall judgment on acceptability. Or, the Agency may find, 4 The MIR is defined as the cancer risk associated with a lifetime of exposure at the highest concentration of HAP where people are likely to live. The HQ is the ratio of the potential HAP
exposure concentration to the noncancer doseresponse value; the HI is the sum of HQs for HAP
that affect the same target organ or organ system.

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