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Management and Effects of Coalbed Methane Produced Water in the Western United States
fidence, including the degree of interconnectivity between coalbeds, groundwater aquifers, and shallow alluvial aquifers.Therefore, mathematical models used to characterize theeffects of CBM water extraction on the connections between surface water and shallowgroundwater aquifers should include independent geological, geochemical (includingage dating), and hydrological measurements in CBM basins and watersheds as inputsto provide a level of reliability for model results. When noncalibrated models are usedto make water management and regulatory decisions, their uncertainties should be explicitly recognized.
Determining the age of CBM produced water—whether the water should be considered “fossil” water and thereby a nonrenewable resource—is a corollary benefit to conducting these kinds of measurements prior to modeling. The scientifically established age of CBMproduced water, and therefore its “renewability,” should be considered in the development and implementation of CBM produced water management regulations.
CBM PRODUCED WATER EFFECTS ON SURFACE WATER AND GROUNDWATER RESOURCES AND THE ENVIRONMENT
The potential effects on the environment of pumping and eventual disposal or use of CBM produced water relate to water quantity, through potential water drawdown or volume addition, and changes in water quality. Baseline water quantity or quality (conditions before CBM extraction begins) could change as a result of CBM operations and produced water management practices, depending on the relative quality of CBM produced water and baseline groundwater or surface water and whether produced water is being extracted or discharged in a given environment.
Groundwater Quantity and Quality
In the Powder River Basin, evidence of drawdown of water levels and hydrostatic heads has been documented in coalbed aquifers as a result of CBM production. However, drawdown effects on shallow groundwater aquifers as a result of CBM production have not, to the committee’s knowledge, been publicly documented and substantiated. This lack of documented effect may be due, in part, to lack of hydraulic connection between coalbed aquifers and shallower aquifers that may be used for domestic water supplies, and in part to a lack of reliable baseline water level data. Thus, resource management or regulatory agencies should require or continue to require collection of baseline groundwater level andquality information for domestic water wells in advance of new CBM drilling activitiesto protect well operators and residents. These data can be compared against groundwater level and quality measurements made during and after CBM development.
Effects on groundwater quality from CBM produced water impoundments relate largely