English

Abstract

Unlined impoundments are widely used for storage of water produced from coal bed natural gas (CBNG) operations in the Powder River Basin, but little published information exists regarding their potential effects on shallow groundwater resources. The Wyoming Department of Environmental Quality (DEQ) requires that CBNG operators characterize shallow groundwater at each CBNG impoundment site. If groundwater is found within the upper 150 to 200-feet of the surface, a well must be completed, a static water level measured and background water quality analyzed. At sites with Class III (Livestock) groundwater the DEQ requires operators to implement a Compliance Groundwater Monitoring Plan which typically entails installation of several wells and quarterly sampling of water quality. The DEQ has maintained a database of groundwater monitoring results from CBNG impoundments since 2004. This is the first published summary of these data. As of December 2006, the database contained a total of 1106 impoundments. Groundwater was not encountered in about 45% of the 1,250 wells and boreholes. The database contains a total of 874 monitoring wells. The permitting status indicates that 75% of impoundments have been exempt from further groundwater monitoring (where no groundwater was encountered or it was Class IV), 15% have on-going monitoring requirements, 7% were not issued a permit, and 3% have their permit status pending. A total of 454 background water samples were analyzed for total dissolved solids (TDS) and other constituents. Approximately 80% of the background TDS concentrations were less than 5,000 mg/L, the class of use limit for class III groundwater. Although there are data gaps, particularly in the early data, this database will evolve and provide a valuable basis for assessing the effects of CBNG impoundments on shallow groundwater.