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E. Surface and Ground Water Monitoring <br />Ground Water <br />Ground water hydrology information can be found in Volumes 4, 5, and 6, Tab 7 <br />of the permit application, and in the Annual Hydrology Reports submitted by <br />Seneca Coal Company. <br />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) Trout <br />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 />Ground water monitoring well locations are shown on Exhibit 7-2 in the permit <br />application. With the reduced permit area, groundwater monitoring will be <br />reduced to two wells; well GW-S41-W monitors the Wadge coal, and well GW- <br />S41-LW 1 monitors the Lennox-Wadge interburden. Details of the revised <br />monitoring plan are discussed on page 2.04.7-2 of the PAP. <br />With the exception of the Quaternary alluvium and replaced spoils, it is thought <br />that each of the identified aquifers is hydraulically discontinuous with each other. <br />This is because of the relatively impermeable (confining) nature of the intervening <br />strata. For this reason, each aquifer will be discussed as a separate entity. <br />Trout Creek Sandstone <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 source of <br />ground water in this region. <br />Water from the Trout Creek Sandstone was used to supply the Seneca II Mine <br />facilities. As the supply well was frequently pumped, reliable depth-to-water <br />information is not available from this site. The Trout Creek Sandstone water is a <br />sodium sulfate type with an average TDS concentration in the range of 900 mg/1. <br />The 70 feet of interbedded sandstone, siltstone, coal and shale act as a confining <br />unit which essentially precludes the vertical migration of water between the Trout <br />Creek Sandstone and the Wolf Creek Coal. Consequently no depletion or <br />degradation of water in this aquifer is anticipated as a result of mining operations <br />at the Seneca II Mine. <br />Wadge Coal and Overburden <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 aquifer. <br />13