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Retrospective Case Study in Southwestern Pennsylvania, Study of the Potential Impacts of Hydraulic Facturing on Drinking Water Resources
Citation:
Wilkin, Rick, T. Lee, C. Ruybal, AND D. Rectenwald. Retrospective Case Study in Southwestern Pennsylvania, Study of the Potential Impacts of Hydraulic Facturing on Drinking Water Resources. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-14/084, 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 for southwestern Pennsylvania, which was conducted in Amwell, Cross Creek, Hopewell, and Mount Pleasant Townships in Washington County, locations that have witnessed unconventional gas production from the Devonian-age Marcellus Shale. Gas production from the Marcellus Shale depends on recent advances in horizontal drilling and hydraulic fracturing technologies to enhance and create fracture porosity and permeability to facilitate gas flow. In this study, water quality samples were collected from domestic wells, springs, and surface water locations during three events in July 2011, March 2012, and May 2013. The sampling locations were selected based upon public recommendations and concerns of landowners about deteriorated water quality potentially linked to nearby drilling, hydraulic fracturing, and the related use of pits and impoundments for storing drilling wastes and flowback/produced water from the Marcellus Shale. The geochemistry of water samples was investigated by analysis of major ions, trace metals, dissolved methane/ethane gas concentrations, volatile organic compounds (VOCs), low-molecular-weight acids, semivolatile organic compounds (SVOCs), glycol ethers, diesel-range organics (DRO), gasoline-range organics (GRO), radiometric constituents, strontium isotope ratios, and selected stable isotopes. Major-ion data collected for this study were compared to historical water quality data obtained from the literature and national water quality databases. Statistical comparisons were made between the data collected for this study and historical data on a countywide basis and on a reduced-area (3-mile-radius) basis in order to specifically focus on historical water quality samples collected near the sampling locations of this study. To help determine whether hydraulic fracturing or processes related to hydraulic fracturing had impacts on water quality, other potential contaminant sources were identified through detailed environmental record searches. The study data indicated a recent ground water impact occurred at sampling locations near the Yeager Impoundment. The impact resulted in elevated chloride levels that exceeded secondary drinking water standards at these sampling locations. The impoundment site was used to store drilling wastes and wastewater associated with the hydraulic fracturing water cycle. Dissolved methane was detected in 24% of the ground water and spring water samples collected in this study. Carbon and hydrogen isotope signatures of methane in domestic well waters were distinct from the reported thermogenic composition of Marcellus Shale gas. Methane occurs naturally in ground water in southwestern Pennsylvania and is present within subsurface glacial deposits, Permian- and Pennsylvania-age coal seams/sedimentary deposits, as well as underlying Devonian-age strata including the Marcellus Shale.
URLs/Downloads:
https://www.epa.gov/hfstudy/report-retrospective-case-study-southwestern-pennsylvania-pdfRetrospective Case Study in Southwestern Pennsylvania
Fact Sheet: Southwestern Pennsylvania Retrospective Case Study