Document Title:

Assessment of contaminants associated with coal bed methane-produced water and its suitability for wetland creation or enhancement projects

Pedro Ramirez Jr

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Extraction of methane gas from coal seams has become a significant energy source in the Powder River Basin of northeastern Wyoming. In Wyoming, coalbed methane (CBM) gas is extracted by drilling wells into coal seams and removing water to release the gas. Each CBM well produces an average of 10 gallons per minute (gpm) of water and a maximum of 100 gpm. Disposal of CBM produced water is accomplished by direct discharge to surface drainages, and also by a variety of other treatment and disposal methods. Untreated CBM produced water discharged to surface drainages is the primary method of disposal provided that the CBM produced water meets Wyoming water quality standards. Water failing to meet water quality standards cannot legally be discharged into surface drainages and is alternately discharged into closed containment ponds for soil-ground water infiltration and evaporation. In 2000 and 2001, we collected and analyzed water from CBM discharges and receiving waters and sediment and biota from CBM produced water impoundments. In 2002, we collected and analyzed water from CBM closed containment impoundments. All the samples were analyzed for trace elements. The biota included pondweed (Potamogeton vaginatus), aquatic invertebrates, fish, and tiger salamanders (Ambystoma tigrinum). One CBM produced water discharge exceeded the chronic criterion for iron and several CBM produced water discharges exceeded the acute criterion for copper. Terminal sinks receiving CBM produced water have the potential for the eventual increase in trace element concentrations in water, sediment and wildlife dietary items such as pondweed and aquatic invertebrates. Waterborne copper, iron, lead, and manganese exceeded chronic criteria in several impoundments receiving CBM produced water. Arsenic, cadmium, nickel, and zinc in sediments from a terminal sink receiving CBM produced water exceeded the threshold effects concentrations for sediment-dwelling organisms. Cadmium and chromium in aquatic invertebrates and pondweed, respectively, from terminal sink sites were elevated. Waterborne selenium concentrations in six of the seven closed containment impoundments and all seven associated CBM discharges ranged from 2.2 to 8.4 :g/L, exceeding the 2 :g/L threshold for bioaccumulation in sensitive species of fish and aquatic birds. Closed containment ponds containing high selenium water may present a risk to aquatic birds using these ponds if the ponds provide a dietary route of exposure through submerged aquatic vegetation or aquatic invertebrates. CBM operators, land managers, and landowners should evaluate the disposal options for CBM produced water on a site by site basis to prevent adverse impacts on soils, groundwater, and surface water as well as fish and wildlife and their habitats.

U.S. Fish and Wildlife Service



U.S. Fish and Wildlife Service - Mountain-Prairie Region, Contaminants Program

Last updated: June 12, 2015