Recent water study finds water quality pre- and post-drilling data to be in line with historic data
Posted: September 24, 2015
Shale gas production from the northern Appalachian Basin has raised concerns about potential impacts to groundwater quality. Donald Seigel, a hydrogeology professor from Syracuse University, and his colleagues recently published an article in Applied Geochemistry that summarizes groundwater quality from 21,044 pre-drilling groundwater samples including 13,040 samples from northeastern Pennsylvania and 8004 samples from southwest Pennsylvania, eastern Ohio, and north-central West Virginia (referred to as the “Western Area”).
This dataset is the most comprehensive water quality dataset published to date related to shale energy development. These groundwater samples were collected as part of Chesapeake Energy Corporation's pre-drilling water supply monitoring program for shale wells they were drilling primarily in the Utica-Point Pleasant and Marcellus formations. The authors evaluated concentrations of major ions and metals and compared them to relevant drinking-water-quality standards. Based upon this evaluation the exceedance of at least one Environmental Protection Agency (EPA) Safe Drinking Water Act standard occurs in 63% of groundwater samples collected and analyzed in northeastern Pennsylvania and 87% in the Western Area. In northeastern Pennsylvania, 10% of the samples exceeded one or more of the United States Environmental Protection Agency’s (USEPA) primary maximum contaminant levels (MCLs) for drinking-water supplies, 46.1% of the samples exceeded one or more of USEPA secondary maximum contaminant levels (SMCLs), and another 7% exceeded one or more of USEPA health advisory or regional screening levels for tap water. In the Western Area 8% of samples exceeded one or more MCLs, 65% exceeded one or more SMCLs, and 15% exceeded one or more health advisory or regional screening levels for tap water. This data shows that water-quality exceedances relate to factors such as sample point location within the groundwater flow system, groundwater chemical type, the geologic formation the well is drawing from, and the well's topographic position (valley versus sideslope or upland).
The comparison of these results to historical groundwater data from northeastern Pennsylvania, which occurred prior to most unconventional shale gas development, shows that the recent pre-drilling geochemical data is similar to historical data. There were no obvious broad changes in variability of chemical quality in this large dataset to suggest oil and gas operation have had an adverse impact. Where saline water was detected it appears to be naturally-occurring native water (ie connate brine)which has not been flushed by circulating meteoric water as opposed to vertical migration of brine from the Marcellus shale or other formations.
Negative impacts to groundwater from shale energy development have not been common, but there have been isolated and localized water quality impacts primarily from drilling operations or due to spills of produced fluids. It is imperative that all measures necessary to protect our valuable water resources be taken in order to meet our society's energy needs while protecting the environment.
David Yoxtheimer, P.G.
Penn State Marcellus Center for Outreach and Research (MCOR)