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permitted mine activities within the North Fork of the Gunnison <br />River drainage basin. The CHIS document is available for review at <br />the Division office. This PHC is based upon information contained <br />within Permit No. C-81-022 (Somerset Minel, and upon the analyses <br />contained within the CHIS far the North Fork Gunnison River. The <br />PHC separately addresses Dotential effects on groundwater and <br />surface water. <br />Effects on Groundwater <br />Mining at the proposed Sanborn Creek area of the Somerset Mine will <br />impact the ground water regime within the immediate area of the <br />proposed operation, but the impact will not cause material damage <br />to the groundwater regime. <br />Though the proposed operation will mine both the C and B seams that <br />have been mined before at the old Somerset Mine, the new Sanborn <br />Creek mine will not be connected to the old workings and will be <br />protected by a 100 foot buffer. The old mine is flooded and the <br />proposed buffer will protect the new operation from possible <br />innundation from the old workings. The 100 foot buffer will be <br />maintained by advance drilling to find the location of the old <br />workings. <br />Mine water inflow into the proposed operation is estimated to be <br />237 gpm or less. The total inflow for the entire old Somerset Mine <br />the year that it was closed down was 234 gpm. The old mine covered <br />an underground area of about 3200 acres; the proposed Sanborn Creek <br />mine will cover an underground area of 596 acres. Therefore it is <br />expected that the inflow into the proposed operation will only be a <br />fraction of that in the old mine. The following are potential <br />sources for inflow: <br />The North Fork of the Gunnison River is 750 feet to the south <br />and 100 feet above the proposed 8-Seam workings and 40 feet <br />above the C-Seam workings. Groundwater is expected to travel <br />down dip from the River through the coal and overburden into <br />the mine workings. Because of the low permeability of the <br />coal and overburden, calculations have shown that these flows <br />should be minor. The flows can be expected to be to the <br />North Fork but with a considerable lag time. There will be a <br />comparable diminution of flow in the North Fork but mine <br />pumpage will return this amount to the river minus that used <br />in the mine. The cone of depression from dewatering of the <br />strata will only extend to the boundary of the North Fork and <br />will not adversely impact any wells. <br />2. There is the potential that the mine may encounter water <br />inflow from faults and fractures. The location of these <br />faults are unknown. The largest fault that the old Somerset <br />mine encountered had a sustained inflow of 120 gpm, which <br />contributed 50% of the total inflow. The Somerset mine has <br />-15- <br />