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An extensive ground water monitoring program which was in existence prior to <br />1981, has identified five aquifers at or near the Seneca II Mine site: (1) <br />Trout Creek Sandstone member of the Mesaverde Group, (2) Wolf Creek Coal, (3) <br />Wadge Coal and Overburden, (4) Quaternary 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 discontinuous <br />with each other. This is because of the relatively impermeable (confining) <br />nature of the intervening strata. For this reason, each aquifer will be <br />discussed as a separate entity. <br />The Trout Creek Sandstone is stratigraphically 70 feet below the Wolf Creek <br />Coal. This 120 foot thick sandstone body is thought to be a significant <br />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 depth-to-water <br />information is not available from this site. The Trout Creek Sandstone water <br />is a sodium sulfate type with an average TDS 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 water <br />between the Trout Creek Sandstone and the Wolf Creek Coal. <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 Wolf <br />Creek Coal were performed at the Seneca II-W Mine site, about 5 miles west of <br />Seneca II Mine, in 1980, These tests indicate that the Wolf Creek Coal is a <br />fairly well confined aquifer which transmits limited amounts of water. One <br />well was pumped at an average of 1.2 gallons per minute for about 3 1/2 hours <br />and produced no observable drawdown at an observation well 20 feet away. <br />Transmissivity values calculated for the Wolf Creek Coal vary between Q.02 <br />ft2 per day (0.149 gallons per day per foot) for well 3WC and 0.001 ft <br />per day (0,007 gallons per day per foot) in the two wells tested, Oue to the <br />low water yield and transmissivity values, the storativity value of the Wolf <br />Creek Coal is estimated to be about 1 X 10-5, Both transmissivity and <br />storativity appear to be quite low due to the highly lenticular and <br />discontinuous nature of the Mesaverde Group. It is thought that <br />transmissivity and storativity values will be variable over large areas. The <br />Wolf Creek Coal aquifer water is a calcium sulfate type with an average TDS <br />value of 745 mg/1. <br />Peabody Coal Company has committed to drilling an additional Wolf Creek Coal <br />well during the 1987 field season. This well will help to determine the cause <br />of the significant loss of head which an adjacent Wolf Creek coal completion <br />has experienced over the past 1.5 years. <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 />-13- <br />