Coalbed Methane Produced Water In The Western Us

aspects of streams and rivers could be adversely affected. The study further proposed that ephemeral streams may become enlarged and potentially change into perennial streams and rivers while receiving CBM produced water discharge. Arthur et al. (2008) proposed that changes in hydrological regime could modify conditions for plants and animals living in the riparian corridor and could lead to adverse environmental impacts.

Although baseline information on flows in ephemeral drainages is generally not available, substantial evidence has shown that regulated, controlled, and managed or unman-aged and/or unregulated14 dynamic alteration in streamflow can result in bank scouring, bottom sedimentation, and increased erosion (Farag et al., 2010; Browning et al., 2005; Maxson and Campbell, 1935). The committee was not able to find published evidence of any widespread effects of this nature in ephemeral streams and gullies receiving CBM produced water discharges. However, at least two instances of land alteration downstream from CBM discharges in ephemeral channels have been documented and are discussed later in this chapter.

Riparian Vegetation

Studies have documented the adverse effects of increased salinity of riparian soils and changes in the natural hydrograph on native riparian vegetation in the southwestern United States. Changes in stream hydrology or salinity generally will result in gradual changes in riparian plant communities (Kirkpatrick et al., 2006). The more saline the soil in riparian areas, the more difficult for plants to extract nutrients and grow (Stearns et al., 2005). Increases in stream salinity or conditions of prolonged or sustained saturation of bank and floodplain sediments generally lead to plant communities dominated by salt-tolerant species. In many instances these species are nonnative.

Stearns et al. (2005) investigated effects of CBM discharge waters on native and introduced vegetation density and diversity in ephemeral drainages in the Juniper Draw Basin in Wyoming. Coulees and ephemeral channels receiving produced water in the Powder River Basin had greater percentages of nonnative plant species than did similar coulees and ephemeral channels not receiving produced water. Stearns et al. concluded that CBM produced water discharge could threaten established native vegetation by invasion of and competition by salt-tolerant species. The invasion of nonnative species, such as may occur in association with CBM produced water discharge, presents challenges for land managers (e.g., Bergquist et al., 2007). Native species provide cover and native wildlife habitat that

14"Unmanaged" encompasses uncontrolled discharge events such as seepage and leaks from impoundments, especially on-channel, discharges resulting from over-topping of impoundments due either to faulty equipment or influxes from upstream rainfall events, and dam failures. "Unregulated" refers to CBM produced water discharges without appropriate permitting. Neither term carries with it any judgment as to intentional or unintentional discharge.

nonnative vegetation does not, and the invasion of nonnative species may include noxious weeks and can alter ecosystem function.

Summary of Ecological Effects

Stressors—constituents or contaminants that put stress on species—of primary interest with respect to CBM produced water discharges into perennial or ephemeral streams or impoundments include several trace elements, TDS, bicarbonate and other ions such as potassium and chloride, and increased turbidity in water due to changing flow with input of CBM water. Of these factors, studies have indicated that increased TDS appears to have potential for greatest direct toxicological impacts to organisms in receiving streams and rivers. Published laboratory studies of TDS and bicarbonate effects on organisms, studies in the field of the effects of CBM produced water on organisms, and interactions between elevated TDS and other stressors and their effects on organisms have all been examined. Because few discharges occur outside the Powder River Basin, most studies have focused on this area.

Laboratory studies regarding TDS and other major ions indicate that exposure to elevated concentrations of one or more constituents can be toxic to some freshwater organisms. The committee's calculations using simple published models to predict water quality toxicity to fish and invertebrates using major ions also indicate that undiluted CBM produced water from many sites within the Powder River Basin could be toxic to many aquatic organisms. Importantly, these results are based on mean concentrations and discharges and on direct and prolonged exposure to undiluted, untreated CBM produced water or its constituents on conventional laboratory test species. In the field, permitted discharges of CBM produced water often require treatment and a defined mixing zone (mixing between CBM produced water and receiving water) within close instream proximity to discharge points. Testing most of the laboratory results against field studies and with species relevant to the study areas in the Powder River Basin has not yet been completed. To date, interactive effects relevant to CBM produced water—whereby exposure to one contaminant or stressor might increase susceptibility to others—also have not been studied.

Laboratory tests examining the acute and chronic toxicity of sodium bicarbonate implicated bicarbonate rather than sodium as a cause of acute toxicity to fathead minnows. Laboratory tests with bicarbonate on other species, including amphibians and invertebrates, exposed to undiluted CBM produced water also show acute to chronic toxicity for some of these organisms. In situ (field) tests conducted in the Tongue and Powder rivers showed mortality to some species when levels of bicarbonate exceeded laboratory toxicity thresholds. However, these results were the result of direct exposure to undiluted CBM produced water, a situation that would be unlikely for prolonged periods in perennial waters where fish are found because of: (1) permitted discharge requirements; (2) the use of the mixing

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