Assessing Shallow Groundwater Quality and Geochemistry in the Fayetteville Shale Gas Production Area, North-Central Arkansas

The Fayetteville Shale is an active source of unconventional natural gas production in north-central Arkansas. Shallow groundwater in this area of the State occurs in fractured bedrock of Pennsylvanian-aged sandstone and shale formations. Numerous households in the area rely on shallow groundwater as a source of domestic supply; for some areas, no other water source is available. Depths of domestic wells range from approximately 25 to 385 feet, with an average of approximately 85 feet. Concerns have been raised by local residents in the Fayetteville Shale production area about the potential threat of hydraulic fracturing to the quality and quantity of domestic well-water supplies, and claims have been made related to problems with production, turbidity, taste, and overall degradation of the quality of water from individual domestic water wells. The USGS worked in cooperation with counties, State and Federal agencies, private entities, and Duke University to assess shallow groundwater quality in 127 domestic wells in the Fayetteville Shale production area. All analyses were within the range of concentrations listed for historic samples taken previous to 1983, chloride concentrations were similar between wells less than and greater than 2 miles from gas-production wells, and carbon isotopes demonstrated that detected methane was biogenic in origin.