EPA noted that the draft findings are specific to Pavillion, where the fracturing is taking place in and below the drinking water aquifer and in close proximity to drinking water wells—production conditions different from those in many other areas of the country.

Background. EPA began investigating water quality concerns in private drinking water wells three years ago at the request of Pavillion residents. Since that time, in conjunction with the state of Wyoming, the local community, and the owner of the gas field, Encana, EPA has been working to assess ground water quality and identify potential sources of contamination.

In the report, EPA notes that water wells in the area overlie the Pavillion gas field, which has 169 production wells extracting gas from the lower Wind River Formation and underlying Fort Union Formation. Hydraulic fracturing in gas production wells occurred as shallow as 372 meters below ground surface with associated surface casing as shallow as 110 meters below ground surface.

Domestic and stock wells in the area are screened as deep as 244 meters below ground surface. With the exception of two production wells, surface casing of gas production wells do not extend below the maximum depth of domestic wells in the area of investigation. At least 33 surface pits previously used for the storage/disposal of drilling wastes and produced and flowback waters are present in the area. The objective of the investigation was to determine the presence, not extent, of ground water contamination in the formation and if possible to differentiate shallow source terms (pits, septic systems, agricultural and domestic practices) from deeper source terms (gas production wells).

Detection of high concentrations of benzene, xylenes, gasoline range organics, diesel range organics, and total purgeable hydrocarbons in ground water samples from shallow monitoring wells near pits indicates that pits are a source of shallow ground water contamination in the area of investigation. When considered separately, pits represent potential source terms for localized ground water plumes of unknown extent. When considered as whole they represent potential broader contamination of shallow ground water. A number of stock and domestic wells in the area of investigation are fairly shallow (e.g., <30 meters below ground surface) representing potential receptor pathways.

Determination of the sources of inorganic and organic geochemical anomalies in deeper ground water was considerably more complex than determination of sources in shallow media necessitating the use of multiple lines of reasoning approach common to complex scientific investigations.

—Draft Report

EPA conducted four sampling events beginning in March 2009 and ending in April, 2011. Ground water samples were collected from domestic wells and two municipal wells in the town of Pavillion in Phase I. Detection of methane and dissolved hydrocarbons in several domestic wells prompted collection of a second round of samples in January, 2010 (Phase II). During this phase, EPA collected additional ground water samples from domestic and stock wells and ground water samples from 3 shallow monitoring wells and soil samples near the perimeter of three known pit locations.

Detection of elevated levels of methane and diesel range organics (DRO) in deep domestic wells prompted the Agency to install 2 deep monitoring wells screened at 233 - 239 meters and 293 - 299 meters below ground surface, respectively, in June 2010 to better evaluate to deeper sources of contamination. The expense of drilling deep wells while utilizing blowout prevention was the primary limiting factor in the number of monitoring wells installed.

In September 2010 (Phase III), EPA collected gas samples from well casing from the deep monitoring wells. In October 2010, EPA collected ground water samples from those wells in addition to a number of domestic wells. In April 2011 (Phase IV), EPA resampled the 2 deep monitoring wells to compare previous findings and to expand the analyte list to include glycols, alcohols, and low molecular weight acids.

Findings in the two deep water monitoring wells. EPA’s analysis of samples taken from the deep monitoring wells in the aquifer indicates detection of synthetic chemicals, such as glycols and alcohols consistent with gas production and hydraulic fracturing fluids; benzene concentrations well above Safe Drinking Water Act standards; and high methane levels. Given the area’s complex geology and the proximity of drinking water wells to ground water contamination, EPA is concerned about the movement of contaminants within the aquifer and the safety of drinking water wells over time.

Findings in the private and public drinking water wells. EPA also updated its sampling of Pavillion area drinking water wells. Chemicals detected in the most recent samples are consistent with those identified in earlier EPA samples and include methane; other petroleum hydrocarbons; and other chemical compounds. The presence of these compounds is consistent with migration from areas of gas production, EPA says. Detections in drinking water wells are generally below established health and safety standards.

While each individual data set or observation represents an important line of reasoning, taken as a whole, consistent data sets and observations provide compelling evidence to support an explanation of data. Using this approach, the explanation best fitting the data for the deep monitoring wells is that constituents associated with hydraulic fracturing have been released into the Wind River drinking water aquifer at depths above the current production zone.

—Draft Report

In the fall of 2010, the US Department of Health and Human Services’ Agency for Toxic Substances and Disease Registry reviewed EPA’s data and recommended that affected well owners take several precautionary steps, including using alternate sources of water for drinking and cooking, and ventilation when showering. Those recommendations remain in place and Encana has been funding the provision of alternate water supplies.

Before issuing the draft report, EPA shared preliminary data with, and obtained feedback from, Wyoming state officials, Encana, Tribes and Pavillion residents. The draft report is available for a 4- day public comment period and a 30-day peer-review process led by a panel of independent scientists.

At the direction of Congress, and separate from this ground water investigation, EPA has begun a national study on the potential impacts of hydraulic fracturing on drinking water resources.

Resources

• Pavillion ground water investigation

• Draft Report