A study that examined the water quality of 127 shallow domestic wells in the Fayetteville Shale natural gas production area of Arkansas (U.S.) found no groundwater contamination associated with gas production, according to a report released on 9th January by the U.S. Geological Survey.

Scientists analyzed water-quality data from samples taken in Van Buren and Faulkner counties in 2011, focusing on chloride concentrations from 127 wells and methane concentrations and carbon isotope ratios from a subsample of 51 wells.

Summary of results:

Groundwater chemistry in the shallow aquifer system in the study area is a result of natural processes.

• Chloride concentrations were not higher in the 2011 samples than in samples from nearby areas collected from 1951 through 1983.
• Chloride concentrations from wells within 2 miles of a gas-production well were similar to concentrations from wells more than 2 miles from a gas-production well.
• Methane concentrations and carbon isotope ratios indicate that almost all methane in groundwater samples is 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.

"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. It does provide a baseline to use to evaluate any possible changes in the future."

The Fayetteville Shale serves as an unconventional gas reservoir across parts of six counties in north-central Arkansas, ranging in thickness from approximately 50 to 550 feet and varying in depth from approximately 1,500 to 6,500 feet below the ground surface. Drilling and production of gas wells began in 2004 and, as of April 2012, approximately 4,000 producing gas wells had been completed in the Fayetteville Shale.