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-:, <br /> III IIIIIIIIIIIIIIII <br />999 <br /> STATE OF COLORADO <br /> <br />DIVISION OF MINERALS AND GEOLOGY _ <br /> <br />F'CO <br />DepanmeN of Natural Resources O <br />~;~ ~~op <br /> <br /> <br />1117 Sherman 51., Rnnm 215 ~Ub <br />~rr~ p <br />~ P <br />~~ <br /> <br />Denver, CO 80207 f <br />' <br />• <br />~„O <br />Phone: 003)866-7567 / <br />FAX: (30 31 8 7 28106 <br /> Koy Romer <br /> Gwcrnn~ <br /> Michael B. Lnng <br /> <br />August 11, 1993 Division Dvttilor <br />Mr. George Patterson <br />Kerr Coal Company <br />P.O. Box 487 <br />Walden, Colorado 80480 <br />RE: Division Concerns, 720 Pit Dewatering, Man Strip Mine (C-SO-006) <br />Dear Mr. Patterson: <br />With the accelerated reclamation of the 720 pit, the Division is concerned that the <br />accumulated water in this pit may require discharging when backfilled overburden displaces <br />the water in the pit. The method, quality and quantity of the discharge is of concern to the <br />Division. Currently the permit application does not specifically have a plan for dewatering the <br />720 pit. To determine the possible affects, and to minimize them, the Division is requesting <br />that Kerr Coal Company address the following concerns. The requested information should <br />be submitted as a technical revision and the permit application updated. <br />1. What is the estimated volume of water that may be discharged and at what maximum rate <br />will the water be discharged? A rough calculation that I performed shows [hat the pit is being <br />bacl~'illed at a rate of about 25 ft 3 per second (given the capacity of the scrapers and a <br />turnaround time of 5 minutes). If the pit is filled, until the water tops over, the pond would <br />receive inflows at the rate of 25 ft s per second. Given the high bentonitic nature of the <br />overburden and the past problems that the mine has had with suspended solids, does pond A <br />have the capacity to treat these inflows and still meet effluent standards? Are the ditches to <br />pond A, sized to handle the overflow from the 720 pit? <br />2. What is the water quality of the pit? <br />3. Kerr should update the dewatering plan to cover the 720 Pit. Page 780-107 aaR of the <br />permit application addresses the dewatering of pit No. 2 to pond H but dewatering of the 720 <br />pit is not addressed. A demonstration should be submitted to show that pond A has the spare <br />capacity to treat the 720 pit pumpage and simultaneously have the capacity to treat the 10 <br />year, 24 hour event. How will the pond level be monitored to maintain the storm capacity? <br />