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basin during the months of June through September has been developed by the <br />operator and included in the statement of probable hydrologic consequences. <br />Mean monthly flow and maximum observed TDS concentrations from monitoring <br />of spoil aquifer wells were used in the analysis. Predicted TDS concentration for <br />the downstream location on Fish Creek was calculated using the mass - balance <br />approach. <br />Results of the analysis on Fish Creek predict a cumulative effect from the <br />Cow Camp and Bond Creek drainages to result in an instream TDS concentration <br />of 607 mg /1 in Fish Creek below the mine during the month of July. This <br />conclusion was based on assumed discharge of 0.2 cfs with a TDS concentration <br />of 2,245 mg /1 from both Cow Camp Creek and Bond Creek. During August and <br />September, no flow in the tributaries is expected to reach Fish Creek as surface <br />flow. <br />An evaluation of the effect of increased TDS concentrations in Fish Creek is <br />discussed in Section XIII of this document entitled Alluvial Valley Floors. Based <br />on the foregoing analysis, the Division makes the finding that the Seneca II Mine <br />site has been designed to minimize off -site surface water impacts. <br />Ground Water <br />Both consolidated and unconsolidated aquifer systems have been identified at and <br />near the Seneca II Mine site. These aquifers may be affected by surface coal <br />mining operations at this site. <br />The Trout Creek Sandstone stratigraphically underlies the Wolf Creek Coal by 70 <br />feet. The intervening strata between the Wolf Creek Coal and the Trout Creek <br />Sandstone, which consists of lenticular sandstone lenses, shale and siltstone, has <br />been identified as a confining layer in this area. This confining layer, which will <br />not be actively disturbed by mining, will mitigate mining related impacts to the <br />Trout Creek Sandstone. There will be no depletion or degradation of the water in <br />this regional aquifer. <br />The Twentymile Sandstone may be slightly impacted by the mining operation. <br />The Bond Creek and Cow Camp Creek drainages intersect the dipping sandstone <br />outcrop adjacent to the southeastern portion of the permit area. The <br />alluvial /colluvial material within each drainage will transmit water discharged <br />from spoils aquifers upgradient in each drainage. This water, which is high in <br />TDS, may recharge the Twentymile Sandstone at the point where the <br />alluvial /colluvial material bisects the outcrop. The potential for water quality <br />degradation due to potential recharge by the poor quality alluvial /colluvial water is <br />the only identified potential impact to this regionally significant aquifer. <br />The Wadge Coal and overburden units are aquifers which have potential for local <br />18 <br />