Potential environmental impacts of shale energy development on proximate flora
Chemicals released from active and producing shale wells have the ability to deposit (e.g., wet or dry) to surrounding plants, soils or waters, but empirical data are lacking. This deposition might affect species and ecosystem health of proximate flora. We examined potential impacts on Pawnee National Grassland (PNG) vegetation due to shale energy development and release of carcinogenic hydrocarbons referred to as BTEX: Benzene, Toluene, Ethyl Benzene, Xylene. The objective of the research was to quantify the deposition and accumulation of BTEX onto proximate flora. We hypothesized that deposition and accumulation of BTEX onto proximate flora would be greater when wells were pumping and would decrease with time since production (4 levels: abandoned, 1980-1990, 2000-2005, 2006-present). Such knowledge is crucial for science-based development of air pollution control and management strategies. In the spring of 2014 a total of 360 vegetation samples were collected from 5 previously and 15 currently producing shale wells on the Pawnee National Grasslands, Colorado. Samples were collected along 50 meter transects in W, NE and SE directions at 20m, 50m and 100m from the production source. Vegetation samples from collection sites were measured for BTEX using a gas chromatograph and flame ionization detector.
Results from the analysis indicate that BTEX were present in a majority of samples. The mean concentrations (BTEX mg/g veg) for all samples were: Benzene 1.36058E-05, Toluene 2.36152E-06, Ethylbenzene 7.88434E-07, o-Xylene 6.87995E-07 and p-Xylene 8.99244E-06. The highest concentration across all samples was for o-Xylene. Deposition and accumulation of BTEX onto proximate flora was significantly greater, F (9.58) and p < 0.001, when wells were pumping, as predicted. Benzene was greater than 30ppm for wells that were pumping natural gas during the time of sample collection. There was a significant difference between production groups for Benzene F (34.65) p < 0.0001, Toluene F (35.11) p < 0.0001 and o-Xylene F (9.58) p < 0.001. Deposition and accumulation of BTEX onto proximate flora decreased with time since production. These results could have implications for restrictions and safety requirements for cattle, other wildlife and humans, with daily exposure in close proximity (e.g., within 100m) of a shale production site. The research provides valuable information to the US Forest Service, local cattle ranchers, the Colorado Oil and Gas Conservation Commission (COGCC) and shale production companies.