Coalbed Methane Produced Water In The Western Us

tee notes that these values reflect effects under circumstances of direct exposure to 100 percent CBM produced water; this situation would be unlikely in perennial waters because of permitted discharge requirements.

Field Assessments of CBM Produced Water Effects

A comprehensive assessment of the potential impacts of CBM discharges on aquatic communities is currently being conducted by the USGS and the Powder River Aquatic Task Group (ATG), a consortium of state, federal, and nongovernmental organizations (Peterson et al., 2009; Farag et al., 2010). The ATG is conducting aquatic and riparian habitat analyses and field surveys of algae, macroinvertebrates, fish, amphibians, and reptiles. Data were collected from 47 locations in the Powder River Basin in 2005 and 2006, with the primary goal of the study to establish current conditions for habitat and aquatic communities in the basin and to quantify the relative influences of stream habitat conditions and water quality characteristics on aquatic communities.

Electrical conductivity of collected water samples was determined to be an important predictor of ecological conditions. Conductivity levels at the points of sampling in the Tongue River were considerably lower than in the Powder River, and species richness showed little variation among sampling sites along the Tongue River. Preliminary results of macroinvertebrate studies showed that macroinvertebrate community composition was best described by a model that included drainage area, streamflow, site location, substrate embeddedness, and specific conductance. Peterson et al. (2009) concluded that the observed longitudinal variation in fish communities from upstream to downstream in the Powder River likely resulted from a complex interplay of habitat, water quality, streamflow, and migration patterns, while much of the spatial variation in aquatic communities among the study sites (e.g. Powder River versus Tongue River) was due to broad geographic factors (e.g., stream headwaters located in mountain versus plains areas) or longitudinal changes.

Collaborative field studies conducted by the BLM, the Montana Cooperative Fishery Unit, Montana State University, and USGS characterized the impacts of CBM on the distribution of fish communities in the Powder River Basin.13 Investigators assessed longitudinal distribution and temporal patterns of fish communities at 57 sites within the basin in 2005. A total of 24 fish species was collected, with zero to eight species collected from streams and rivers that received CBM produced water discharges and one to 12 species in streams and rivers that did not receive CBM produced water ("control" streams and rivers). Differences in the number of species and community composition in streams and rivers assessed were thus examined against the locations of CBM produced water discharges. Some

13See "Task 7" at www.netl.doe.gov/technologies/oil-gas/Petroleum/projects/Environmental/Federal_Lands/ 15467Task2.html (accessed February 24, 2010).

species were found only in streams and rivers receiving CBM produced water discharges, while other species were found exclusively in streams and rivers to which no CBM produced water had been discharged. Researchers noted considerable uncertainty regarding using the data to assess the direct effects of CBM discharges on fish assemblages.

Instream toxicity studies were conducted by researchers at the University of Wyoming to assess potential toxic effects of CBM produced water on fish (Heath and Meyer, 2008). Researchers concluded that, despite elevated concentrations of ammonia and bicarbonate, acute toxic effects were mitigated by mixing of produced water with instream flows and by biogeochemical interactions between CBM produced water and sediments in the stream (discussed previously).

Effects on Riparian Environments

Riparian areas are the interface between dry uplands and water bodies. These areas are generally vegetated by hydrophilic plant communities and potentially contribute substantially to the ecological and environmental functionality and stability of ephemeral and perennial water courses. Numerous studies have investigated the actual or potential effects of discharge of CBM produced water on riparian environments (e.g., Busch and Smith, 1995; Vandersande et al., 2001; Glenn and Nagler, 2005; and Smith et al., 2009).

Typically, the effects of CBM produced water discharge on riparian environments are a consequence of changes in the hydrology (frequency, duration, availability, or quantity of water) and the chemistry (mainly salinity) or soil substrates of the receiving stream (stream bottom, channel, and shoreline). The primary potential or observed adverse effects of CBM discharge to streams and rivers and riparian systems are (1) changes in the timing and amount of streamflow, (2) increased stream bank erosion and instability, (3) increased suspended sediment concentrations and/or turbidity, (4) downstream sediment deposition, (5) changes in riparian plant communities, and (6) increased stream water and sediment salinity. Studies of these effects are discussed in the following sections.

Ephemeral Drainages

The lower and less frequent flows of ephemeral streams compared to perennial streams and rivers can result in greater expression of adverse effects of CBM discharges on the hydrology and water quality of the ephemeral drainages than perennial streams and rivers. As early as 2001 the Montana DEQexpressed concern about the potential effects of sustained discharges of CBM produced water to ephemeral streams. Regele and Stark (2001) proposed that CBM produced water discharges could destroy vegetation in stream channels, increase erosion and deposition of sediment in streams and reservoirs, and degrade water quality. Consequently, algae, aquatic invertebrates, fish, amphibians, and other biological

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