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 Antero’s 2010 sampling. In addition, five COPCs identified from the Bell-Melton Ranch data set that were not measured in the 2008 air toxics study were identified as COPCs. 74 contaminants were selected as COPCs. The following 15 contaminants were retained as COPCs because the maximum detected concentration exceeded 1/10 the EPA RSL or they were identified as COPCs in the Bell-Melton Ranch data set. • 1,2,3-Trimethylbenzene • 1,2,4-Trimethylbenzene • 1,3,5-Trimethylbenzene • 1,3-Butadiene • Benzene • Ethylbenzene • m&p-Xylene • n-Hexane • n-Nonane • n-Pentane • Acetaldehyde • Formaldehyde • 1,4-Dichlorobenzene • Methylene chloride • 2-Hexanone There was no EPA RSL for the remaining 59 COPCs, which were retained because their detection frequency was 5 percent or greater. Two possible EPCs were evaluated. The first EPCs were determined as described in Section 2.5.1 and are summarized in Table 2-11. The maximum observed concentration was assigned as the second EPC because concentrations of COPCs in ambient air have been measured during completion activities involving up to 3 wells and more wells may be completed at one time during Antero’s proposed project. The maximum detected concentrations were observed in the sample collected downwind of and approximately 200 feet from the center of an Antero well pad during flow back operations. In addition, samples were collected over a 24-hour interval which may have diluted out peak emissions during flow back operations. The two EPCs (the maximum detected concentration and the 95%UCL) provides a range for evaluation of risk. 2.5.4 Chemicals of Potential Concern Grab Samples Table 2-7 summarizes the selection of COPCs from grab samples collected when residents noticed odors they attributed to natural gas operations during the 2005 -2007 ambient air monitoring study and from grab samples collected by Antero in August 2010. The following 11 chemicals were selected as COPCs because the maximum detected concentration exceeded 1/10 the EPA RSL or they had a detection frequency of greater than 5 percent and no EPA RSL was available Appendix D page 17
Appendix D Screening Level Human Health Risk Assessment February 2011 Battlement Mesa, Colorado Health Impact Assessment Colorado School of Public Health • Benzene • Ethylbenzene • m&p-Xylene • o-Xylene • Toluene • Chloroform • Acetaldehyde • Formaldehyde • Hexaldehyde • Crotonaldehyde • Benzaldehyde Two possible EPCs were evaluated. The first EPCs were determined as described in Section 2.5.1 and are summarized in Table 2-7. The maximum observed concentration was assigned as the second EPC because the maximum possible exposure was desirable in the evaluation of acute exposure for the maximum exposed individual (MEI). The two EPCs (the maximum detected concentration and the 95%UCL) provides a range for evaluation of risk. 2.6 Statistical Observations for Select COPCs 2.6.1 Comparison Between Ambient Air Samples and Well Completion Samples Concentrations of COPCs in the ambient air samples collected at the Bell-Melton Ranch Monitoring Station from 2005 to 2010 and ambient air samples collected during well completion activities in 2008 and 2010 were compared using the Mann-Whitney U test in EPA’s ProUCL version 4.00.05 software (EPA 2010). The Mann-Whitney U test was used because the data is not normally distributed. Table 2-12 summarizes the results. Concentrations from the well completion samples were significantly higher than the concentrations from the Bell-Melton Ranch monitoring station at an alpha level of 0.05 for all COPCs tested, with the exception of n-pentane. The concentrations of n-pentane from the well completion samples were higher than the concentrations from the Bell- Melton Ranch monitoring station (p=0.06), although not at an alpha level of 0.05. The mean benzene concentration from the well completion samples is approximately six times greater than the mean benzene concentration from Bell-Melton Ranch. The mean concentration of 1,2,4-trimethylbenzene from the well completion samples is 24 times greater than the mean 1,2,4-trimethylbenzene concentration from Bell-Melton Ranch. Similar results were observed when the concentrations of COPCs from the ambient air samples collected at the Battlement Mesa Monitoring station were compared to the concentrations of COPCs from the ambient air samples collected during well completion activities. Appendix D page 18
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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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