Quakes in Arkansas: New Cause for Concern About Drinking Water?

CNN reports that central Arkansas experienced over three dozen quakes in the past week. An Arkansas Geologic Survey scientist described that number of quakes occurring in such a short time as being "Powerball sort of odds," while emphasizing that he did not know whether the quakes were natural or man-induced. The two strongest tremors were measured at 3.4 and 3.5 on the magnitude scale.

This somewhat disturbing news came on the heels of better news for the gas industry last week, also out of Arkansas. In that news, Duke scientists sampled 127 drinking water wells over the Fayetteville Shale formation in central Arkansas and found no indication that fracking had contaminated any of the drinking water wells.

When talking quakes, one needs to distinguish between wells fracked for gas production and the use of deep wells for disposal of wastewater. One obvious difference is that fracking for production rapidly increases pressure for a short period of time and then releases that pressure as wastewater and production fluids flow back to the surface, whereas deep well disposal pressurizes rock formations for an extended period of time.

Thus far, scientists have made the link between quakes and deep disposal wells -- not production wells. The U.S. Geological Survey concluded that disposal wells near fault lines can cause earthquakes by increasing fluid pressure along faults, causing them to fracture. In 2011, scientists attributed a magnitude 5.6 quake in Oklahoma to wastewater disposal near a fault line. Columbia University scientists came to the same conclusion about earthquakes just outside of Youngstown, Ohio in 2011.

The concern is not solely, or even primarily, about personal and property damage at the surface, it is whether the quakes will cause fractures that ultimately lead wastewater to escape and contaminate fresh drinking water aquifers.

There is increasing evidence of a link between deep wastewater disposal wells and earthquakes, which emphasizes the need for the natural gas industry to fund research into developing better ways to efficiently manage its wastewater, other than by putting it down a hole under pressure.

New Duke study finds no contamination from fracking in Arkansas

Duke scientists sampled 127 drinking water wells over the Fayetteville Shale gas development area of Arkansas, where 4,000 wells have been drilled. The samples were analyzed for radioisotopes and chemicals and those results were compared to analysis of flowback water from gas wells. The scientists found no evidence that natural gas development using fracking contaminated shallow drinking water wells.

This is the same group at Duke's Nicholas School of the Environment that found direct evidence of methane contamination in drinking water wells near shale gas drilling sites in the Marcellus Shale basin of northeastern Pennsylvania, as well as possible connectivity between deep brines and shallow aquifers, but no evidence of contamination from fracking fluids.

According to Avner Vengosh, a professor of geochemistry who participated in the study, "the take-home message is that regardless of the location, systematic monitoring of geochemical and isotopic tracers is necessary for assessing possible groundwater contamination."

Pennsylvania does not require this sort of systematic, geochemical and isotopic monitoring.