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collected from 1981 to 2002. TDS in Bond Creek has risen from 550 mg/1 in 1987 <br />to 2,838 mg/l in 2002. The operator has suggested that TDS levels in Bond Creek <br />and Cow Camp Creek will stabilize after mining activities cease, as has been <br />observed in the portion of the Grassy Creek drainage where mining has ceased. <br />A prediction of TDS loading which could be expected to occur in both the <br />Fish Creek and Grassy Creek basins during the months of June through September <br />has been developed by the operator and included in the statement of probable <br />hydrologic consequences. Mean monthly flow and maximum observed TDS <br />concentrations from monitoring of spoil aquifer wells were used in the analysis. <br />Predicted TDS concentrations for downstream locations on both Fish and Gtassy <br />Creeks were calculated using the mass-balance approach. <br />Results of the analysis indicate that a maximum TDS of 2341 mg/1 would occur <br />during September at a location below the mine on Grassy Creek. A corresponding <br />flow of 0.84 cfs would result. <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 of <br />607 mg(1 in Fish Creek below the mine during the month of July. This conclusion <br />was based on assumed discharge of 0.2 cfs with a TDS concentration of 2245 mg/1 <br />from both Cow Camp Creek and Bond Creek. During August and September no <br />flow in the tributaries is expected to reach Fish Creek as surface flow. <br />There is no agricultural use of water immediately downstream of the Seneca II Mine <br />on Grassy Creek. Due to the small quantity of flow contributed to the Yampa River <br />by Grassy Creek, the increased concentration of TDS produced in the Yampa River <br />would_be minnnal, and not preclude the bene€cial uses of this wafer. An evahuttion <br />of the effect of increased TDS concentrations in Fish Creek is discussed in Section <br />XIII of this document entitled Alluvial Valley Floors. Based on the foregoing <br />analysis, the Division makes the fmding that the Seneca IT Mine site has been <br />designed to minimize off-site surface water impacts. <br />Ground Water <br />Both consolidated and unconsolidated aquifer systems have been identified at and <br />neaz the Seneca II Mine site. These aquifers maybe affected by surface coal mining <br />operations at this site. <br />The Trout Creek Sandstone stratigraphicallyundeAies 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 azea. This confming layer, which will not <br />be actively disturbed by mining, will mitigate mining related impacts to the Trout <br />Creek Sandstone. There will be no depletion or degradation of the water in this <br />26 <br />