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 3.5.2 All Residents Living Near Well Pads Chronic Exposure Assumptions and Intake Equations Only the ambient air exposure pathway was quantitatively evaluated for the residents living near well pads because data on which to estimate surface soil EPCs is not available and exposure to surface water run-off from pads is of short duration. The exposure area for contaminants in ambient air is homes and yards near well pads. Based on Garfield County’s 2008 Air Toxic’s Study, the highest concentrations of SNMOCs in ambient air were observed during well completion activities (Garfield County 2008, Table 2-11). Therefore, subchronic EPCs for ambient air were estimated from ambient air samples collected at four separate well completion sites in Garfield County’s 2008 air toxics study and Antero’s 2010 sampling. In the 2008 study, four ambient air samples (one from each cardinal direction) were collected at distances ranging from 130 to 430 feet from the well pad center at four separate well completion sites (Paul Reaser, personal communication 7/6/2010). In Antero’s sampling, eight ambient air samples (two from each cardinal direction) were collected at 350 and 500 feet from the well pad center at the Watson Ranch Pad on the Southwest boundary of the Battlement Mesa PUD. The maximum detected concentration and 95% UCL from these samples were used to provide a range of subchronic EPCs. If a chemical was not measured in the Air Toxics Study or Antero’s sampling, but was measured at the Bell- Melton Ranch monitoring station, the maximum concentration measured at the Bell- Melton Ranch monitoring station was used as the subchronic EPC. All subchronic EPCs were from 24-hour integrated samples. The EPC for chronic exposure for residents living near a well pad was estimated by calculating a time weighted average (TWA) from the subchronic EPCs described in the preceding paragraph and chronic EPCs described in Section 3.5.1. The following assumptions regarding the chronic scenario for residents living near well pad are used in this HHRA based on the EPA methodology and Antero’s proposed plan: • The duration of Antero’s project, from preparation of the first well pads to abandonment of the last well will be 30 years. • A resident lives, works, and otherwise stays within the Battlement Mesa PUD for 24 hours per day, 350 days per year, for a 30-year time period. • The resident’s home is within ½ mile of a well pad. • Well completion activities, including plug pull outs, hydraulic fracturing, and flow back occur over two weeks for each well on the well pad. This assumes some overlap between activities and wells. • For a 20 well pad, well completion activities (flow back and hydraulic fracturing) will occur over 10 months. • Some residents live within ½ mile of more than one well pad and are exposed to emissions from well completion activities for at least 20 months. Appendix D page 25
Appendix D Screening Level Human Health Risk Assessment February 2011 Battlement Mesa, Colorado Health Impact Assessment Colorado School of Public Health • The resident lives, works, or otherwise stays at the home during the duration of well completion activities. • The air that the resident breathes, both while indoors and outdoors, contains the same concentrations of contaminants measured in the 2008 Air Toxics Study and Antero’s 2010 sampling during the duration of the well completion activities. • The air a resident breathes, both while indoors and outdoors, after the well completion activities contains the same concentration of contaminants measured in the Bell-Melton Ranch ambient air samples. • Air contaminant concentrations will remain constant over the 20-month period of well completion. • Air quality, as reflected by the Bell-Melton Ranch ambient air results, will remain relatively constant over the entire 30-year duration of Antero’s proposed project. • The lifetime of a resident is 70 years. Table 3-2 summarizes intake rates for ambient air, which were calculated by the intake equations presented in Section 3.5.1. TWA EPCs for residents living near well pads were calculated as follows: EPCS+c = (EPCc x EDc/ED) + (EPCs x EDs /ED) EPCc = Chronic exposure point concentration (µg/m 3 ) EDc = Chronic exposure duration = 340 months EPCs = Subchronic exposure point concentration (µg/m 3 ) EDs = Subchronic exposure duration = 20 months ED = Total exposure duration = 360 months 3.5.3 All Residents Living Near Well Pads Subchronic Exposure Assumptions and Intake Equations Only the ambient air pathway was quantitatively evaluated for the all resident subchronic exposure scenario because data because data on which to estimate surface soil EPCs is not available and exposure to surface water run-off from pads is of short duration. The exposure area for contaminants in ambient air is homes and yards near well pads. The subchronic EPCs described in Section 3.5.3 were used for the subchronic exposure scenario. The following assumptions for subchronic exposure all residents, including children and elderly adults, living near 2 or more well pads to contaminants in ambient air are used in this HHRA based on EPA methodology. • Well completion activities, including plug pull outs, hydraulic fracturing, and flow back occur over two weeks for each well on the well pad. This assumes some overlap between activities and wells. • For a 20 well pad, well completion activities (flow back and hydraulic fracturing) will occur over 10 months. Appendix D page 26
Page 1 and 2: Draft Battlement Mesa HIA, Revision
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Page 87 and 88: 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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Appendix D: Human Health Risk Assessment - Garfield County ...

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