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 Summary of Modifications: The following modifications to the September 2010 version of the risk assessment were made based on stakeholder comments and data that became available after September 2010. 1. Near a well pad has been defined as living within ½ mile of a well pad. This definition is based on odor complaints in July 2010 from residents living ½ mile from the Watson Ranch pad. 2. An elderly adult is defined as aged 65 years or greater has been added as a receptor. 3. A subchronic exposure scenario of 20 months for exposure to air emissions during well completion operations has been added. This is based on comments received in the citizen’s stakeholder meeting that some residents live within ½ mile of more than one of the proposed well pads. Many individuals live within ½ mile of two of the proposed pads and some live within ½ mile of three of the proposed pads. The subchronic exposure scenario was evaluated for all receptors (children, adults, and elderly adults). Previously an intermediate exposure of 10 months was used, based on well-completion activities for 20 wells on one well pad. 4. An acute exposure scenario of 7 days has been added for adults, including elderly adults. 5. A baseline risk was estimated for Battlement Mesa residents based on ambient air samples collected at the Battlement Fire Station from September to November 2010. 6. The exposure point concentrations used in the chronic risk assessment for all Battlement Mesa residents and for residents living near (within ½ mile) a well pad were updated to include data collected through November 2010. 7. The exposure point concentrations for the subchronic exposure (previously defined as an intermediate exposure) used in the time-weighted average to estimate chronic exposure point concentrations for those living near a well pad were revised as follows. The maximum concentration and the 95%UCL from the 2008 Air Toxics Study and Antero’s August 2010 sampling was used to provide a range for subchronic exposure point concentration. If a contaminant was not measured in these studies, the maximum concentration from the Bell- Melton Ranch Monitoring station was used as the subchronic exposure point concentration. All subchronic exposure point concentrations were determined from data obtained from 24-hour integrated samples. 8. Subchronic toxicity factors have been found for most contaminants of potential concern (COPCs) and were used to estimate the subchronic risk. If a subchronic toxicity factor was not available, the chronic toxicity factor was used, per EPA guidance (EPA 1989). A more thorough discussion of the bias this introduces has been added to the uncertainty section. 9. The exposure point concentrations for the acute exposure to contaminants in air were revised as follows. The maximum concentration and 95% UCL from the 2005 to 2007 grab samples collected when odors were noticed and the grab Appendix D page 11
Appendix D Screening Level Human Health Risk Assessment February 2011 Battlement Mesa, Colorado Health Impact Assessment Colorado School of Public Health samples Antero collected in their August 2010 sampling were used to provide a range for the exposure point concentration. All acute exposure point concentrations were determined from data collected via grab sampling. 10. If acute toxicity factors were not available, intermediate toxicity factors were used, per EPA guidance (EPA 1989). A more thorough discussion of the bias this introduces has been added to the uncertainty section. 11. The averaging time for the acute exposure of a child to surface water has been revised from 365 days to 7 days. Appendix D page 12
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Appendix D Screening Level Human He
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1 of 2 Table 2-1 Comparison of MRLs
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Table 2-2 Comparison of MRLs from 2
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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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