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Chapter IV <br /> d. Mine Discharges. <br /> In 1980 five separate mines were operating in Coal Basin. Each of these mines <br /> discharged excess ground water (not used for dust suppression, etc., generally in the <br /> spring) to the outside or to adjoining streams (NPDES permits 002 and 019). <br /> The outcrop of the coal seam is at 10,000 feet and the seam drops downdip into the <br /> mountain at 12 degrees. The coal seam is under 3,000 feet of cover under Huntsman <br /> Ridge and some 2,000 feet below the Muddy Creek valley to the west of Coal Basin. <br /> The affected aquifers have a very low permeability. There are no known users of <br /> ground water from the Mesaverde Group aquifers within a two-mile radius from the <br /> edge of the mine. Therefore, no impacts to ground water from the Mesaverde Group <br /> aquifers should result from dewatering the mine workings. When mining in Coal Basin <br /> is terminated, the water levels in the aquifers will rise to the pre-mining ground water <br /> levels in 12 to 24 months. This was the case with Nos. 4 and 5 mines. <br /> The present measured mine discharge rates vary seasonally between 40 to 360 GPM <br /> per operating mine. These flows may increase as mining moves farther down the dip of <br /> the strata. However, past experience has shown this not to be significant. <br /> In 1980 the total peak flow from all five mines was approximately 1,000 GPM. In 1986 <br /> the total peak flow from Nos. 1 and 2 Mines was approximately 1,000 GPM. Note: as <br /> No. 3 mine fills during the period of inactivity, there may be increased pressure on the <br /> aquifers adjacent to No. 1 mine, possibly increasing the flow in the longer slopes of the <br /> No. 1 mine. <br /> In contrast, the U.S. Steel Somerset mine's peak pumping rate in 1985 was 20,000 <br /> GPM. <br /> Water quality in the mines has been monitored since 1977 for the following parameters: <br /> Flow MGD <br /> pH 6.5-9.0 <br /> T.D.S. 35.-70. <br /> Iron 3.5-7.0 <br /> Oil-Grease 10 <br /> From 1977 to 1985, the following data was recorded for each mine <br /> (Note: Nos. 3, 4 and 5 were inactive and not pumping during a part of that time). <br /> • <br /> 10 <br />