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<br />The base of the Third White sandstone, the lowest of the three White <br />sandstones, is stratigraphically located about 20-50 feet above the H coal <br />seam, a seam to be recovered at the Trapper Mine. The combined thicknesses of <br />the White sandstones is about 450 feet. Separating each of the sandstone <br />units is a thin series of shales and thin coals. Only the lowest White <br />sandstone, the Third, is proposed to be disturbed by mining. When mining is <br />complete, the Third White sandstone will be in direct hydrologic contact with <br />reclaimed spoils. The First and Second White sandstones are separated from <br />mining by sufficient stratigraphic thickness and surface distance such that <br />the potential for impacts is minimal. Therefore, only the Third White <br />sandstone is discussed in detail in this document. <br />The Third White sandstone attains a thickness of about 150 feet in the <br />vicinity of the Trapper Mine. 1t is stratigraphically situated about 20-50 <br />feet above the H coal seam. A series of about 50 feet of shales and coals <br />separate it from the stratigraphically higher Second White sandstone. This <br />zone creates a sufficient impermeable harrier to allow for wells cor~pleted in <br />the aquifer to exhibit confined characteristics. The applicant has obtained <br />transmissivity and storage coefficient values for the aquifer. This <br />information is needed in case a pollutant-migration model would have to be <br />developed. <br />The water quality of the Third White sandstone can he generally categorized as <br />poor for domestic purposes and good for irrigation and livestock-watering <br />purposes. Total dissolved solids values range from 602 to 982 mg/1, The <br />range in pH is from 6.6 to 10.65. The water is a calcium bicarbonate type. <br />Sulfate, iron, and TDS concentrations consistently exceed drinking water <br />standards. <br />The Third White sandstone aquifer generally recharges at its outcrop and may <br />discharge at its subcrop into the Yampa River alluvial aquifer. The northern <br />limits of mining at the Trapper Mine will remove portions of the Third White <br />sandstone. The aquifer will subsequently be in direct hydrologic <br />communication with reclaimed spoils. Projected impacts to the aquifer are <br />discussed later in this document. <br />The two major alluvial aquifers in the vicinity of the Trapper Mine are those <br />associated with the Yampa and Williams Fork Rivers. Most surface drainage <br />from the Trapper Mine flows away from the Williams Fork River and towards the <br />Yampa River. No mining-related impacts are projected for the Williams Fork <br />River or alluvial aquifer. <br />The north edge of the proposed mining is located about 2 to 3 miles from the <br />Yampa River. The applicant has determined that surface drainage from the <br />Trapper Mine contributes only 0.07 cfs/mil to the Yampa River flow. The <br />applicant found that ground water contribution to the base flow of the Yampa <br />Fiver in the Big Bottom area is undetectable (p. 2-533 of the permit <br />application). Therefore, the Trapper Mine i s not expected to produce any <br />impacts on the Yampa or Williams Fork Rivers or associated alluvial aquifers. <br />Ground water use is discussed nn p. 2-524 of the permit application. There <br />are about 50 registered private wells in the vicinity of the Trapper Mine. <br />The locations of these wells are shown on Map H31. <br />-16- <br />