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Removing coal in the underground workings will cause ground water inflow <br /> into the mine void, resulting in drawdown of the potentiometric surface in the <br /> Wadge coal seam around the perimeter of the workings. The drawdown will <br /> extend into beds immediately above and below the coal seam. Maximum <br /> inflow of ground water into the workings is predicted to be 75 gallons per <br /> minute, including less than 2 gallons per minute of predicted spoil leachate <br /> inflow from surface mine pits that are up dip from the underground workings. <br /> Section 2.05 .6(3)(b)(111) of the permit application contains an analytic <br /> simulation of the drawdown for three points in time after commencement of <br /> underground mining: 2 years, 5 years (end of first permit term), and 35 years <br /> (30 years after first permit term), with no mining beyond the current non-treat <br /> room and pillar proposal. Figure 2.05.6-F4.2 in the permit application shows <br /> predicted drawdown contours for the Wadge coal potentiometric surface. The <br /> contours indicate drawdown at the location of the seam's outcrop on the <br /> northeast flank of the Fish Creek Anticline will exceed 50 feet during the <br /> initial five-year permit term and then will recover to a drawdown of less than <br /> 5 feet after mining ceases. The Wadge coal seam at this location is within the <br /> Trout Creek Sandstone-Twentymile Sandstone outcrop belt that has been <br /> reported as contributing to Grassy Creek flows (page 38 of U. S. Geological <br /> Survey publication titled Evaluation of the upper part of the Mesaverde <br /> Group_Northwestern Colorado. Water-Resources Investigations Report 90- <br /> 4020, by S.G. Robson and Michael Stewart). Seepage out of the outcrop belt <br /> was reported as contributing approximately 20% of Grassy Creek's instream <br /> flow when sampled in July and September in 1986. The Wadge coal seam <br /> comprises roughly 5% of the aggregate thickness of likely permeable units in <br /> the outcrop belt, assuming the seam is 10 feet thick, and the Trout Creek and <br /> Twentymile Sandstones are in aggregate 200 feet thick. If the coal seam's <br /> contributions to Grassy Creek flows are eliminated by PSC's drawdown (which <br /> PSC's analysis indicates is possible),and assuming the Wadge coal seam <br /> contributes 5%of the outcrop belt's total contribution to Grassy Creek flows, <br /> then PSC's drawdown could reduce Grassy Creeks' flows by 1% (a 5% <br /> reduction of 20%of Grassy Creek's flow). A 1%reduction in flow in Grassy <br /> Creek will not be enough to impair the use of Grassy Creek water. <br /> There currently are no users of surface water on Grassy Creek. <br /> Underground mine water that accumulates in the down dip end of <br /> underground mine workings will seep into the unmined rock in the walls,roof, <br /> and floor of the workings. The quality of this leachate is expected to be <br /> similar to native ground water in the Wadge coal seam and the roof and floor <br /> rock because large amounts of gob (waste rock) are not expected to be <br /> produced during non-retreat room and pillar mining. PSC predicts that a <br /> plume of mine water will advance outward from the workings at a <br /> Page 18 of 27 <br />