USGS: No Water Contamination From Drilling in Fayetteville Shale

The State Journal
10 January 2013
By Pam Kasey

A study examining the water quality of shallow domestic wells in the Fayetteville Shale natural gas area of Arkansas found no groundwater contamination associated with gas production, the United States Geological Survey announced Jan. 9.

"This new study is important in terms of finding no significant effects on groundwater quality from shale gas development within the area of sampling," said USGS Director Marcia McNutt on releasing the report, "Shallow Groundwater Quality and Geochemistry in the Fayetteville Shale Gas-Production Area, North-Central Arkansas, 2011." McNutt emphasized the survey's hundred-year history of unbiased information on natural resources.

The Fayetteville Shale, like the Marcellus Shale, is an unconventional gas reservoir that is exploited through horizontal drilling and hydraulic fracturing. Drilling and production began there in 2004, several years ahead of the Marcellus.

The scientists analyzed water quality data from samples taken in Van Buren and Faulkner counties in 2011. They focused on chloride concentrations from 127 wells and on methane concentrations and carbon isotope ratios from a subsample of 51 wells.

Chloride is a naturally occurring ion that is found at elevated levels in waters associated with gas production. It's a good indicator of whether chemicals used during hydraulic fracturing are reaching groundwater, the survey said in its media release. Chloride concentrations from this study were not higher than samples taken from nearby areas from 1951 through 1983. In addition, chloride concentrations from wells within two miles of a gas production well were similar to concentrations from wells more than two miles from a gas production well.

Methane is the primary component of natural gas, but it also can be found naturally in shallow shale formations in the Fayetteville Shale area that are used as sources of water for domestic supplies. Methane concentrations and carbon isotope ratios indicated that almost all of the methane in groundwater samples was naturally occurring as a result of biological processes in shallow shale formations used as a source of water for domestic purposes and did not originate from the Fayetteville Shale.

Groundwater chemistry in the shallow aquifer system in the study area is a result of natural processes, the study's authors concluded.

"None of the data that we have looked at as part of this study suggests that any groundwater contamination is resulting from natural gas production activities," said USGS hydrologist Tim Kresse.

"However, this study does not speak to other wells that were not sampled, every chemical used during the hydraulic fracturing process, or water quality changes that might take longer to occur," Kresse acknowledged. "It does provide a baseline to use to evaluate any possible changes in the future."