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• 2.05.6(3) Protection of the H~}~drolo¢ic Balance <br />Water could eventually accumulate in the mine workings and result in mine water flow through the <br />coal seams into the North Fork of the Gunnison River. Although the operator does not believe either <br />the B-Seam or the C-Seam will become totally inundated with water, a worst case analysis was <br />prepared to estimate the seepage from the coal seams. Darcy's Law was utilized to estimate the <br />seepage from the coal seams as follows: <br /> Darc 's Law Q=Kia <br />Flooded K -cm/sec H -Head w -width h- L- I- O -GPM <br />Working of coal Seam OutCfOD H/w <br /> illar Hei ht Len th <br />8 Seam 4 X 10$ 30 309 20 4223 0.1 0.5 <br />B Seam 5 X 105 30 309 20 4223 0.1 6.0 <br />C-Seam 4 X 10-0 75 159 8 3964 0.47 0.9 <br />C Seam 5 X 10'5 75 159 8 3964 0.47 11.0 <br />Area=hxL <br />K is from MCC's TR-080 documents and provides a range of seepage rates. <br />Bear's existing discharge permit provides for the discharge of mine water directly to the North Fork <br />of the Gunnison River through outfall OOl. The mine water discharge initially flowed at <br />approximately 20 gpm. As of April 1998, the flow increased to about 35 gpm. In order to account <br />• for additional Flow from the mine, it will be assumed that the mine water flow equals 50 gpm. The <br />maximum measured TDS value for the mine water is 4090 mg/l. This TDS value will be utilized for <br />the mine discharge and the mine seepage. The total worst case mine seepage is calcualted above and <br />totals 17.0 gpm. The range in estimated outcrop seepage from the B-Seam and C-Seam is 1.4 to 17 <br />gpm. <br />According to data supplied by the USGS, the annual seven day minimum flow for the North Fork of <br />the Gunnison River is 25 cfs. This low flow value occurred February 17, 1978, is for the period of <br />record from 1934 through 1995 and is measured upstream of the Town of Somerset, CO. <br />As shown above, the total flow through the alluvium is 136 gpm. Of that total Flow, approximately <br />41 gpm is subject to contamination from the coal stockpile area. The quality of the contaminated <br />water should be similar to the water quality in well AA-l . For the period of 1987 though 1996, the <br />maximum TDS measured in AA-1 was 2890 in 1995. <br />The maximum TDS measurement at the upstream North Fork of the Gunnison River monitoring <br />station during 1997 was 120 mg/I. The following table presents the estimated affect the mine <br />discharge, mine outcrop seepage and alluvial flow will have on the quality of water in the North Fork <br />of the Gunnison River: <br />• 2.Oj-j ici Rev. 7/9R <br />