The U.S. Environmental Protection Agency (EPA) has undertaken five case studies in the Marcellus, Barnett and Bakken shales and the Raton Basin on the impact of hydraulic fracturing (fracking) on drinking water sources as part of its multi-year review of the well stimulation technique used in unconventional plays.

EPA in late December issued an interim update of its review of fracking; a draft report is expected in 2014 (see Shale Daily, Dec. 24). As part of its investigation, the federal agency is conducting two types of case studies: retrospective and prospective.

Retrospective case studies, now being done in the five drilling sites, are investigating reported drinking water resource contamination reports where fracking already has occurred.

Prospective case studies also are planned at sites where fracking would be used after research begins to allow EPA to sample and characterize the site before, during and after drilling, fluid injection, flowback and gas production. The prospective case studies, still in their early stages, are being designed and developed with help from some of EPA’s industry partners.

The retrospective case studies offered reams of material from across the country. EPA had to whittle its prospects down, so stakeholders from coast to coast were invited to identify locations to investigate.

From thousands of potential sites submitted, more than 40 locations were nominated by EPA and five cases ultimately were chose to study, each offering some unique perspective on drilling’s impact on drinking water supplies.

EPA chose Bradford County, PA, and a small portion of adjoining Susquehanna County as one case study because of the extensive activity in the Marcellus Shale, coincident with a large number of homeowner complaints regarding the appearance, odor and possible health impacts associated with water from domestic wells.

Cabot Oil & Gas Corp. has been involved in a multi-year investigation into supposed water contamination from its gas drilling in Susquehanna County, of which EPA has found no evidence (see Shale Daily, March 19).

In Washington County, PA, EPA is conducting a case study in response to homeowner complaints about changes to water quality and quantity, including impacts to private drinking water wells, specifically increased turbidity, discoloration of sinks and transient organic odors since Marcellus drilling increased.

The groundwater in Washington County is variable, and EPA had to sample domestic and surface water wells based on interviews with individuals about water quality and timing of water quality changes in relation to gas production activities.

In Wise County, TX, a rural area in the Barnett Shale, a case study is being done based on homeowner concerns also about changes in the groundwater quality that could be related to increased fracking, or to farming operations, EPA said.

There have been complaints of changes in drinking water quality clustered in three distinct locations: two near Decatur and one near Alvord.

“Because of the standard well design in the county, it is not possible to sample directly from drinking water wells nor is it possible to measure water levels to establish groundwater flow gradients and direction,” so EPA has sampled domestic and industrial water wells at the tap as close to the wellhead as possible and before any water treatment had occurred.

In Colorado’s Las Animas and Huerfano counties, which are in the Raton Basin, EPA is investigating potential drinking water impacts from coalbed methane extraction.

The Dunn County, ND, case study site in Killdeer was chosen by state officials to specifically examine water resource impacts that might have occurred following a well blowout in September 2010. At that time an uncontrolled release of fracking fluids and formation fluids happened near the Killdeer Aquifer, the main source of drinking water for the city. Monitoring wells have been installed. Two rounds of sampling have been conducted so far at domestic, municipal and supply water wells.