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West Elk Mine <br />2.04 -60 Rev. 06/05- PR10, 03/06- PR10, 04/06- PR10, 09/07- PR12; 05/22- MR462 <br /> <br /> <br />The most immediate assessment of whether a geologic formation can be considered an aquifer is to <br />assess whether water supply wells (a demonstration of beneficial use) have been completed into the <br />formation. As shown in Table 3A, there are 29 permitted wells within the West Elk Mine permit <br />boundary. Of these, 17 have reported well yields and 13 have provided well depths (ten wells less <br />than 100 feet, three wells between 140 and 191 feet). These values range from a low of 0.0 gpm to <br />a high of 30.0 gpm. The four highest reported yields are from wells drilled to a depth of 10 to 63 <br />feet in Sections 9, 10 and 11 (i.e., in the alluvium of the North Fork). These four wells are not <br />completed in the bedrock members of the Mesaverde Formation. The other 13 wells with reported <br />yields have a range of 0.0 to 4.0 gpm (seven wells have reported yields of 0.0 gpm) and an average <br />production rate of 0.65 gpm. Closer inspection of the remaining 6 wells with reported well yields <br />above 0.0 gpm shows that all but one is permitted as a monitoring well. As such, only one of the 29 <br />permitted wells appears to have obtained a useable supply (2.0 gpm reported) for beneficial use <br />(stock watering). This well has a depth of 140 feet, within the active groundwater flow zone where <br />there is hydraulic communication with the surface and thus dependence on annual recharge events. <br />Given the lack of beneficial use of these formations as a water supply, it is concluded that these <br />formations are not aquifers. Further evidence to support this conclusion is provided by the low <br />permeability data described later in this section. <br /> <br />Wells have been completed in a variety of formations for varying purposes. Formations in which <br />groundwater monitoring data have been collected include the Rollins Sandstone, various members <br />of the Mesaverde Formation, and colluvial and alluvial deposits. <br /> <br />In addition to water level data collection, hydrogeologic characteristics (i.e. transmissivity, <br />hydraulic conductivity, and yield) of many of these formations have been obtained from pumping <br />and slug test analysis. Transmissivity values from pumping tests were estimated from Lohman <br />(1975), using the following equation: <br />Q = 4 π T s 2.30 log  2.25Tt  <br /> <br /> <br />Where: <br />Q = discharge (gal/day) <br />T = transmissivity (gal/day/ft) <br />r = radius of the well (ft) <br />t = duration of pumping (days) <br />s = drawdown (ft) <br />10  r2 S  <br />S = storage coefficient (estimated 0.001) <br /> <br />The following sections discuss each of the monitored formations within the permit area and their <br />hydrogeologic characteristics. For the most part, the bedrock units represent the inactive <br />groundwater zone particularly at depths greater than about 500 feet below the ground surface and a <br />distance of approximately 1,000 feet inward from exposed cliff faces. The colluvium and alluvium, <br />along with the near surface exposures of the bedrock units, represent the active groundwater zone.