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An extensive ground water monitoring program which was in existence prior <br />to 1981, has identified five aquifers at or near the Seneca II Mine <br />site: (1) Trout Creek Sandstone member of the Mesaverde Group, <br />(2) Wolf Creek Coal, (3) Wadge Coal and Overburden, (4) Quaternary <br />alluvium, and (5) replaced spoils. <br />With the exception of the Quaternary alluvium and replaced spoils, it is <br />thought that each of the identified aquifers are hydraulically <br />discontinuous with each other. This is because of the relatively <br />impermeable (confining) nature of the intervening strata. For this <br />reason, each aquifer will be discussed as a separate entity. <br />The Trout Creek Sandstone is stratigraphically 70 feet below the Wolf <br />Creek Coal. This 120 foot thick sandstone body is thought to be a <br />significant source of ground water of areal extent in this region. <br />Water from the Trout Creek Sandstone is used to supply the Seneca II Mine <br />facilities. As the supply well is frequently pumped, reliable <br />depth-to-water information is not available from this site. The <br />Trout Creek Sandstone water is a sodium sulfate type with an average TDS <br />concentration of about 1040 mg/1. <br />The 70 feet of interbedded sandstone, siltstone, coal and shale act as a <br />confining unit which essentially precludes the vertical migration of <br />water between the Trout Creek Sandstone and the Wolf Creek Coal. <br />Consequently no depletion or degradation of water in this aquifer is <br />anticipated as a result of mining operations at the Seneca II Mine. <br />The Wolf Creek Coal seam, being a fairly uniform body, is capable of <br />transmitting and storing small amounts of water. Aquifer tests of the <br />Wolf Creek Coal were performed at the Seneca II-W (dine site, about <br />5 miles west of Seneca II Mine, in 1980. These tests indicate that the <br />Wolf Creek Coal is a fairly well confined aquifer which transmits limited <br />amounts of water. One well was pumped at an average of 1.2 gallons per <br />minute for about 3 1/2 hours and produced no observable drawdown at an <br />observation well 20 feet away. Tran~missivity values calculated for the <br />Wolf Creek Coal vary between 0.02 f~ per day (0.149 gallons per day <br />per foot) for well 3WC and 0.001 ft per day (0.007 gallons per day per <br />foot) in the two wells tested. Due to the low water yield and <br />transmissivity values, the storativity value of the Wolf Creek Coal is <br />estimated to be about 1 X 10- Both transmissivity and storativity <br />appear to be quite low due to the highly lenticular and discontinuous <br />nature of the Mesaverde Group. It is thought that transmissivity and <br />storativity values will be variable over large areas. The Wolf Creek <br />Coal aquifer water is a calcium sulfate type with an average TDS value of <br />745 mg/1. <br />The Wadge Overburden is considered to be an aquifer in this area and for <br />purposes of this discussion, is collectively grouped with the Wadge Coal <br />aquifer. <br />Aquifer tests performed in the Wadge Coal seam indicate that the Wadge <br />aquifer exhibits a semi-confined condition with a transmissivity value of <br />377.1 gallons per day per foot (gpd/f t). Wadge water levels, dependent <br />upon well proximity to the recharge area, show some seasonal variation. <br />-15- <br />