2008-03-31_PERMIT FILE - C1980007A (34)

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Vest Elk Mine 0 Groundwater uantity Characteristics Over 238 exploration holes have been drilled on or near the West Elk Mine coal lease area. Records and consultation with project geologists indicate that water was encountered only sporadically in the Mesaverde Formation, indicating groundwater is localized and of limited areal extent. As defined in the CDMG rules, an aquifer is "a zone, stratum or group of strata acting as a hydraulic unit that can store or transmit water in sufficient quantities for beneficial use." Based on information presented in the next several sections of this document (i.e., permeability analyses, and water level observations), it is the contention of MCC that none of the geologic members of the Mesaverde Formation are aquifers within the West Elk Mine block. The most immediate assessment of whether a geologic formation can be considered an aquifer is to assess whether water supply wells (a demonstration of beneficial use) have been completed into the formation. As shown in Table 3A, there are 29 permitted wells within the West Elk Mine permit boundary. Of these, 17 have reported well yields and 13 have provided well depths (ten wells less than 100 feet, three wells between 140 and 191 feet). These values range from a low of 0.0 gpm to a high of 30.0 gpm. The four highest reported yields are from wells drilled to a depth of 10 to 63 feet in Sections 9, 10 and 11 (i.e., in the alluvium of the North Fork). These four wells are not completed in the bedrock members of the Mesaverde Formation. The other 13 wells with reported yields have a range of 0.0 to 4.0 gpm (seven wells have reported yields of 0.0 gpm) and an average production rate of 0.65 gpm. Closer inspection of the remaining 6 wells with reported well yields above 0.0 gpm shows that all but one is permitted as a monitoring well. As such, only one of the 29 permitted wells appears to have obtained a useable supply (2.0 gpm reported) for beneficial use (stock watering). This well has a depth of 140 feet, within the active groundwater flow zone where there is hydraulic communication with the surface and thus dependence on annual recharge events. Given the lack of beneficial use of these formations as a water supply, it is concluded that these formations are not aquifers. Further evidence to support this conclusion is provided by the low permeability data described later in this section. Wells have been completed in a variety of formations for varying purposes. Formations in which groundwater monitoring data have been collected include the Rollins Sandstone, various members of the Mesaverde Fonmation, and colluvial and alluvial deposits. • 2.04-62 Revised June 200.1 PRIG, March 2006; Rev. Apri12006 PRIO, Sep. 2007PR12