A recent study of Marcellus Shale natural gas production found that drinking water contamination came from a thermogenic, rather than biological, source. The study was headed by Duke University biology professor Rob Jackson and aided by researchers from the University of Rochester and California Polytechnic State University. The results of the study were published June 24th, 2013 in the Proceedings of the National Academy of Sciences to build on the same team’s May 9th, 2011 study, reported in Greenwire, which found a link between Marcellus shale drilling and contamination of Pennsylvania drinking water wells. The study also responds to an industry study, reported in EnergyWire, which called methane in the area’s drinking water “ubiquitous.”

The study found that some gas in supposedly contaminated wells comes from layers of rock between the productive Marcellus gas formation and the surface. The study included 81 new drinking water wells in six counties in northeastern Pennsylvania, and 60 previously sampled wells in Pennsylvania and New York’s Otsego County. The concentration of methane in drinking wells was about six times higher within 1 kilometer of drilling wells than homes farther away. The concentration of methane was above the federal threshold for immediate remediation in 12 homes, 11 of which fell within the one kilometer radius of a well.

The researchers analyzed samples of ethane and propane, gas elements not found in shallow, “biogenic” gas, and found that these elements were more common closer to wells. Contamination is expected to have been a result of faulty well construction, partially linked to the Cabot Oil & Gas Corp.’s previous allegedly faulty construction in the area.

Jackson was also part of a USGS team that studied alleged groundwater contamination from production of the Fayetteville Shale in Arkansas, and found no groundwater contamination associated with gas production there. Another recent USGS study of 20 water wells in Pennsylvania’s Sullivan County showed the presence of thermogenic gas before drilling in two of the wells, demonstrating that thermogenic gas can get into water wells without drilling.