Perry C, Tachovsky JA, Ke M, Urban J, Haws L. 2012. Natural gas exploration and production in the Barnett Shale: Assessment of exposures to volatile organic compounds (VOCs). Presented at the Society of Toxicology’s 51st Annual Meeting, March 11-15, San Francisco, CA.
There are an estimated 13,500 producing natural gas wells in the Barnett Shale (BS) formation, which spans approximately 24 counties in north central Texas (TX). Since 2002, natural gas production in the BS region has substantially increased, and the region contains the largest onshore gas fields in the US. The Texas Commission on Environmental Quality (TCEQ) has over 20 monitors in the region, 8 of which are in relatively close proximity to natural gas exploration and production operations (six AutoGCs analyzing 46-64 VOCs and two canister monitors analyzing 105 VOCs). Maximum 1-hour AutoGC and 24-hour canister data were compared to available federal and state acute health-based toxicity values. Annual average concentrations were compared to available federal and state chronic health-based toxicity values. The measured concentrations were also compared to typical US and TX-specific background concentrations, as well as to TCEQ odorbased values. While there were a few acute exceedances of odor-based values, our analyses showed that none of the 1-hour or 24-hour concentrations exceeded any of the acute health-based toxicity values. For the annual average concentrations, there were exceedances of some federal chronic health-based values for benzene and 1,3- butadiene at all six AutoGCs, but these levels were all below TCEQ chronic healthbased values and typical US or TX-specific background concentrations. In terms of the canister monitors, the annual average concentrations of 16 chemicals exceeded some federal health-based toxicity values. However, with the exception of 1,2-dibromoethane and methyl butyl ketone, all of the annual average concentrations were below the TCEQ chronic health-based values. Importantly, all measurements for 1,2-dibromoethane and methyl butyl ketone were non-detected, and the exceedances are solely the result of conservatively assuming that these chemicals were present at a concentration equal to ½ DL. Collectively, these data do not indicate any concern regarding potential exposures to VOCs associated with these types of operations.