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Retrospective Case Study in Wise County, Texas, Study of the Potential Impacts of Hydraulic Fracturing on Drinking Water Resources
Citation:
Beak, D., M. Overbay, AND S. Mravik. Retrospective Case Study in Wise County, Texas, Study of the Potential Impacts of Hydraulic Fracturing on Drinking Water Resources. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-14/090, 2015.
Impact/Purpose:
As a component of the EPA’s National Study of the Potential Impacts of Hydraulic Fracturing on Drinking Water Resources (US EPA, 2012), five retrospective case studies were conducted to investigate reported instances of drinking water resource contamination in areas of natural gas development and use of hydraulic fracturing technology. These studies were intended to inform primary research questions related to the hydraulic fracturing water cycle (US EPA, 2012).
Description:
This report describes the retrospective case study in north central Texas, conducted at three locations in Wise County where both conventional and unconventional gas production occurred in the past. Currently unconventional gas production occurs from the Mississippian-aged Barnett Shale. Gas production from the Barnett Shale depends upon recent advances in horizontal drilling and hydraulic fracturing technologies to enhance and create fracture porosity, permeability, and gas flow. Water-quality samples were collected from 16 domestic wells and 4 surface water bodies at three locations within Wise County during five sampling rounds in September 2011, March 2012, September 2012, December 2012, and May 2013. Additionally, three production wells (gas wells) were sampled—two that had been completed in the Barnett Shale and one that had been completed in the overlying Boonesville Bend Conglomerate formation. The geochemistry of water samples was investigated by analyzing major ions, trace metals, methane/ethane gas concentrations, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), glycol ethers, diesel and gasoline range organics (DRO and GRO), and selected stable isotopes (δ18OH2O, δ2HH2O, and 87Sr/86Sr). Major ion data collected from this study were compared to historical water-quality data retrieved from the literature and national water-quality databases. These data sources provide water-quality data for samples collected before 1993 (except NWIS), and therefore, before Barnett Shale gas recovery. Statistical comparisons using analysis of variance and Kruskal-Wallis tests were made between the data collected from this study and both the historical data on a countywide basis and on a reduced-area (3-mile radius) basis to specifically focus on historical water samples collected near the sample locations of this study.Comparison of historical data to study data collected suggested no apparent impacts to groundwater at two of the three study locations. In the third study area, three study wells were identified as impacted. A comparisons of study data with historical data revealed two wells were impacted based on differences in several parameters, most notably chloride and specific conductivity. A more detailed investigation using site-specific background data indicated that a third well was also impacted. Based on the screening of potential sources of impacts, formation brines were the only source that was consistent with the observed impacts to two of the study wells. In the third impacted well the screening indicated two potential sources exist for the impact observed, brines and landfill leachate. However, the evaluation of potential source or sources of the impact was limited based on a lack of available site specific data. Site specific data was only available for formation brines while literature data was used for other potential sources of impacts. This limited the capability of geochemical fingerprinting and determining a more definitive source of the impacts.
URLs/Downloads:
https://www.epa.gov/sites/production/files/2015-06/documents/wise_report_508_km_0.pdfFact Sheet: Wise County, Texas Retrospective Case Study