HUMAN HEALTH RISK ASSESSMENT OF AIR EMISSIONS FROM THE DEVELOPMENT OF UNCONVENTIONAL NATURAL GAS RESOURCES
Technological advances (e.g. directional drilling, hydraulic fracturing), have led to increases in unconventional natural gas development (NGD), raising questions about health impacts. We estimated health risks for exposures to air emissions from a NGD project in Garfield County, Colorado with the objective of supporting risk prevention recommendations in a health impact assessment (HIA). Previously, we used EPA guidance to estimate chronic and subchronic non-cancer hazard indices and cancer risks from exposure to hydrocarbons for two populations: (1) residents living > ½ mile from wells and (2) residents living ≤ ½ mile from wells. These results showed that residents living ≤ ½ mile from wells are at greater risk for health effects from NGD than are residents living > ½ mile from wells. Subchronic exposures to air pollutants during well completion activities present the greatest potential for health effects. The subchronic non-cancer hazard index (HI) of 5 for residents ≤ ½ mile from wells was driven primarily by exposure to trimethylbenzenes, xylenes, and aliphatic hydrocarbons. Chronic HIs were 1 and 0.4. for residents ≤ ½ mile from wells and > ½ mile from wells, respectively. Cumulative cancer risks in our previous study were 10 in a million and 6 in a million for residents living ≤ ½ mile and > ½ mile from wells, respectively, with benzene as the major contributor to the risk. Risk assessment can be used in HIAs to direct health risk prevention strategies. Our previous work indicated that future risk management approaches should focus on reducing exposures to emissions during well completions. Here, we will summarize our findings to date and discuss recommendations for future risk management studies.