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Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules
An SV in any of the tiers is not an estimate of the cancer risk or a noncancer HQ. Rather, an SV represents a high-end estimate of what the risk or HQ may be. For example, facility emissions resulting in an SV of 2 for a non-carcinogen can be interpreted to mean that we are confident that the HQ
would be lower than 2. Similarly, facility emissions resulting in a cancer SV of 20 for a carcinogen means that we are confident that the cancer risk is lower than 20-in-1 million. Our confidence comes from the healthprotective assumptions that are incorporated into the screens: we choose inputs from the upper end of the range of possible values for the influential parameters used in the screens, and we assume food consumption behaviors that would lead to high total exposure. This risk assessment estimates the maximum hazard for mercury through fish consumption based on upper bound screens. As discussed above, the maximum mercury Tier 2 noncancer SV
based upon the fisher scenario resulted in an SV less than 1.

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4. Environmental Risk Screening Results As described in section III.A of this preamble, we conducted an environmental risk screening assessment for the Mercury Cell ChlorAlkali Plant source category for the following pollutants: HCl and mercury methyl mercury and mercuric chloride. However, as noted above, we subsequently determined that the HCl emissions are due to non-category sources such as co-located HCl production.
In the Tier 1 screening analysis, methyl mercury and divalent mercury resulted in exceedances of ecological benchmarks by two facilities. Divalent mercury emissions had Tier 1
exceedances for the following benchmarks: Surface soil threshold levelinvertebrate communities by a maximum SV of 4. Methyl mercury had Tier 1 exceedances for the following benchmarks: No Observed Adverse Effect Level NOAELavian ground insectivores woodcock by a maximum SV of 6.
A Tier 2 screening analysis was performed for divalent mercury and methyl mercury. In the Tier 2 screening analysis, divalent mercury emissions had no Tier 2 exceedances. Methyl mercury had Tier 2 exceedances for one facility exceeding the following benchmark: Surface soil NOAEL for avian ground insectivores woodcock by a maximum SV of 2 with 0.1 percent of the soil area being above an SV of 2.

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For HCl, only one facility reported emissions. The average modeled concentration around this facility i.e., the average concentration of all off-site data points in the modeling domain did not exceed any ecological benchmark. In addition, each individual modeled concentration of HCl i.e., each off-site data point in the modeling domain was below the ecological benchmarks.
However, as explained above, after further investigation, we conclude that the reported HCl emissions are due to non-category sources.
5. Facility-Wide Risk Results The EPA estimated inhalation risk based on facility-wide emissions to be 0.3-in-1 million, with an 0.0001 excess cancer cases per year, or one case every 10,000 years. Emissions of metals arsenic, chromium VI, and nickel from non-category sources account for 100
percent of the cancer incidence. No one is exposed to cancer risk greater than or equal to 1-in-1 million see Table 1 of this preamble. The maximum chronic noncancer TOSHI value for the source category was the same for both actual emissions and allowable emissions with an HI less than 1 0.05 for respiratory risks driven by chlorine emissions from the mercury cell building.
6. What demographic groups might benefit from this regulation?
To examine the potential for any environmental justice issues that might be associated with the source category, we performed a demographic analysis, which is an assessment of risks to individual demographic groups of the populations living within 5 km and within 50 km of the facilities. In the analysis, we evaluated the distribution of HAP-related cancer and noncancer risks from the mercury cell chlor-alkali plant source category across different demographic groups within the populations living near the two facilities.23
Results of the demographic analysis indicate that, for three of the 11
demographic groups, age greater than or equal to 65, age greater than or equal to 25 years of age without a high school diploma, and people below the poverty level, the percentage of the population living within 5 km of facilities in the source category is greater than the corresponding national percentage for 23 Demographic groups included in the analysis are: White, African American, Native American, other races and multiracial, Hispanic or Latino, children 17 years of age and under, adults 18 to 64
years of age, adults 65 years of age and over, adults without a high school diploma, people living below the poverty level, people living two times the poverty level, and linguistically isolated people.

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the same demographic groups. When examining the risk levels of those exposed to emissions from mercury cell chlor-alkali plant facilities, we find that no one is exposed to a cancer risk at or above 1-in-1 million or to a chronic noncancer TOSHI greater than 1.
The methodology and the results of the demographic analysis are presented in a technical report, Risk and Technology ReviewAnalysis of Demographic Factors for Populations Living Near Mercury Cell Chlor-Alkali Plant Source Category Operations, available in the docket for this action.
C. What are our proposed decisions regarding risk acceptability, ample margin of safety, and adverse environmental effect?
1. Risk Acceptability As explained in section II.A of this preamble, the EPA sets standards under CAA section 112f2 using a two-step standard-setting approach, with an analytical first step to determine an acceptable risk that considers all health information, including risk estimation uncertainty, and includes a presumptive limit on MIR of approximately 1-in-10 thousand 54 FR
38045, September 14, 1989. The EPA
weighed all health risk measures and information, including science policy assumptions and estimation uncertainties, in determining whether risk posed by emissions from the source category is acceptable.
As described above, the maximum cancer risk for inhalation exposure to actual and allowable emissions from the Mercury Cell Chlor-Alkali Plant source category is 0.004-in-1 million, which is more than four orders of magnitude below 100-in-1 million, which is the presumptive upper limit of acceptable risk. The EPA estimates emissions from the category would result in a cancer incidence of 0.0000003 excess cancer cases per year, or one case every 3
million years. Furthermore, as described above, the facility estimated to pose those cancer risks is no longer operating as a mercury cell facility. Inhalation exposures to HAP associated with chronic noncancer health effects result in a TOSHI of 0.05 based on actual and allowable emissions, 20 times below an exposure that the EPA has determined is without appreciable risk of adverse health effects. Exposures to HAP
associated with acute noncancer health effects result in an HQ less than or equal to 2 based upon the 1-hour REL for elemental mercury, and when the maximum off-site concentration is compared with the AEGL2 and ERPG
2, the maximum acute noncancer HQ is
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