Appendix D: Human Health Risk Assessment - Garfield County ...

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Appendix D Screening Level Human Health Risk Assessment February 2011 Battlement Mesa, Colorado Health Impact Assessment Colorado School of Public Health • An adult lives and otherwise stays at the home for 24 hours per day for 7 days. • The air the adult breathes, both while indoors and outdoors, contains the same concentration of contaminants measured during odor events in the 2005-2007 ambient air study and by Antero during their August 2010 well completion activities. • The concentration of contaminants in ambient air will stay constant over the 7-day period. Appendix D page 29
Appendix D Screening Level Human Health Risk Assessment February 2011 Battlement Mesa, Colorado Health Impact Assessment Colorado School of Public Health 4 Toxicity Assessment This section presents the toxicity assessment. The purpose of the toxicity assessment is to evaluate available evidence regarding the potential for a particular contaminant to cause adverse health effects in exposed individuals and how the appearance and severity of these adverse effects depends on the dose of the contaminant. In addition, the toxic effects of a chemical frequently depend on the route of exposure (oral, inhalation, dermal), the duration of exposure (acute, subchronic, chronic or lifetime), age, sex, diet, family traits, lifestyle, and state of health. As in all risk assessments there are uncertainties in the toxicity assessment that may lead to both over and underestimation of the risk estimates presented in this HHRA. Section 6 discusses this uncertainty. 4.1 Selection of Toxicity Values The following hierarchy was used to compile a list of inhalation toxicity values for the HHRA. For COPCs identified in ambient air, inhalation values established specifically by the State of Colorado were given priority over all other sources of toxicity values, followed by EPA’s Air Toxics Website (http://www.epa.gov/ttn/atw/toxsource/summary.html). The State of Colorado has not established toxicity values for the COPCs identified in this HHRA. If values were not available the Air Toxics Website, toxicity values were filled (in order of preference) EPA’s Integrated Risk Information System (IRIS), EPA’s Provisional Peer-Reviewed Toxicity Values (PPRTVs), and other applicable secondary sources (e.g., California EPA; ATSDR). Inhalation toxicity values were available for 19 out of 82 COPCs as presented in Table 4-1. Inhalation toxicity values were not available for the remaining 63 COPCs presented in Table 4-2. These COPCs were omitted altogether from the quantitative inhalation risk estimation. A list of oral toxicity values was complied for the HHRA (in order of preference) from EPA’s IRIS and the Agency for Toxic Substances and Disease Registry (ATSDR). Oral toxicity values were available for all the surface water COPC presented in Table 4-3. Dermal toxicity values can be extrapolated from oral toxicity values by adjusting the oral RfD by its oral absorption factor, per EPA guidance (EPA 1989). The oral absorption factor for all the COPCs identified in surface water was 100 percent. Therefore, the dermal RfD is equivalent to the oral RfD. 4.1.1 Cancer Toxicity Values Potential carcinogens are grouped according to the likelihood that the chemical is human carcinogen, depending on the quality and quantity of carcinogenic potency data for a given chemical. Group A – Human Carcinogen (sufficient evidence of carcinogenicity in humans) Appendix D page 30
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Page 87 and 88: 1 of 2 Table 2-1 Comparison of MRLs
Page 89 and 90: Table 2-2 Comparison of MRLs from 2
Page 91 and 92: Table 2-3 Comparison of MRLs for 20
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Chemical Number of samples Table 2-
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Table 2-4 Summary Statistics and Se
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Number of Samples Table 2-7 Summary
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Table 2-8 Ambient Air Summary Stati
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Table 2-8 Ambient Air Summary Stati
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Chemical Table 2-9 95% UCLs and Sel
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2010) 4 of 4 Table 2-9 95% UCLs and
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Chemical Table 2-10 95% UCLs and Se
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Chemical Table 2-11 95% UCLs and Se
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Statistic Table 2-12 Comparison of
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Table 3-1 Cancer and Non-Cancer Air
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Table 3-2 Cancer and Non-Cancer Air
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Table 3-3 EPCs and Surface Water In
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Table 4-1 Cancer and Non-Cancer Inh
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4 of 4 Table 4-1 Cancer and Non-Can
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Chemical Available Toxicity Values
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Table 5-1 Baseline Risk Characteriz
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Table 5-2 Comparison of EPCs to BTV
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1 of 2 Table 5-4 Chronic Risk Chara
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1 of 1 Table 5-5 Subchronic Risk Ch
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Table 5-7 Acute Risk Characterizati
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Table 6-1 Chemicals Identified from
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Benzene, Ethylbenzene, and d m&p-Xy
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Sources Potential Releases Exposure
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Excess Canc cer Risk per one Millio
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