title: Stream measurements locate thermogenic methane fluxes in groundwater discharge in an area of shale-gas development.
abstract: The environmental impacts of shale-gas development on water resources, including methane migration to shallow groundwater, have been difficult to assess. Monitoring around gas wells is generally limited to domestic water-supply wells, which often are not situated along predominant groundwater flow paths. A new concept is tested here: combining stream hydrocarbon and noble-gas measurements with reach mass-balance modeling to estimate thermogenic methane concentrations and fluxes in groundwater discharging to streams and to constrain methane sources. In the Marcellus Formation shale-gas play of northern Pennsylvania (U.S.A.), we sampled methane in 15 streams as a reconnaissance tool to locate methane-laden groundwater discharge: concentrations up to 69 μg L(-1) were observed, with four streams ≥ 5 μg L(-1). Geochemical analyses of water from one stream with high methane (Sugar Run, Lycoming County) were consistent with Middle Devonian gases. After sampling was completed, we learned of a state regulator investigation of stray-gas migration from a nearby Marcellus Formation gas well. Modeling indicates a groundwater thermogenic methane flux of about 0.5 kg d(-1) discharging into Sugar Run, possibly from this fugitive gas source. Since flow paths often coalesce into gaining streams, stream methane monitoring provides the first watershed-scale method to assess groundwater contamination from shale-gas development.
authors.affiliation: †U.S. Geological Survey Utah Water Science Center, Salt Lake City, Utah 84119, United States.
authors.forename: Victor M
authors.initials: VM
authors.lastname: Heilweil
authors.affiliation: ‡Earth and Environmental Systems Institute and Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
authors.forename: Paul L
authors.initials: PL
authors.lastname: Grieve
authors.affiliation: ‡Earth and Environmental Systems Institute and Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Hynek
authors.affiliation: ‡Earth and Environmental Systems Institute and Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Brantley
authors.affiliation: §Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, United States.
authors.forename: D Kip
authors.initials: DK
authors.lastname: Solomon
authors.affiliation: ∥U.S. Geological Survey Pennsylvania Water Science Center, New Cumberland, Pennsylvania 17070, United States.
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Risser
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D004777:Environment; D004784:Environmental Monitoring; D005740:Gases / Q000032:analysis; D060587:Groundwater / Q000032:analysis*; D006838:Hydrocarbons / Q000032:analysis; D008697:Methane / Q000032:analysis* / Q000378:metabolism; D008962:Models, Theoretical; D005741:Noble Gases / Q000032:analysis; D061329:Oil and Gas Fields; D000066388:Oil and Gas Industry; D010414:Pennsylvania; D014481:United States; D014874:Water Pollutants, Chemical / Q000032:analysis*; D062066:Water Resources; D014881:Water Supply; D060986:Water Wells
chemical_list: D002247:Carbon Isotopes; D005740:Gases; D006838:Hydrocarbons; D005741:Noble Gases; D014874:Water Pollutants, Chemical; D008697:Methane