2013-01-29_PERMIT FILE - C1981022A (3)

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Sazicv: - 2.05.6 While this average TDS value e somewhat elevated, it u not atypical of TDS values for deeper • ground water in this area. Groundwater movement a limited, the potential volume of downgradient discharge from the old mine workings u extremely small compared with the volume of the overall ground water system, and any upgradient seepage will be limited in voltune and comprise a negligible portion of surface drainage contributions so it does not represent a significant potential impact. The previous operator discharged mine water at Bear Creek and Elk Creek under an CDPS point source discharge permit. The water met all applicable discharge effluent requiretnenu without treatment. OMI began discharging water from the Sanborn Creek Mine though approved CDPS Outfall 011 during June 1992. During the last two quarters of 1992, discharge water from the Sanborn Creek Mine exceeded the dscharge limits for total suspended solids on two occazions. OMI took the following steps to address this temporaryproblem and reestablish compliance: Aug. 1992: A 1.5 million-gallon sump waz developed in the B-Seam Nov. 1992: A chemical treatment system was installed using Nalco 92DR043 Clarification Aid to reduce the required settling time that did improve water clarity. Dec. 1992: A second chemical, Nalco 9810 flocculent, was added to the chemical treatment system to work in conjunction with the 92DR043 to further enhance the chemical treatment. Mar. 1993: The water/chemical interface point was moved approximately 300 feet closer to the main sump to prevent breakage of the flocculent chain which improved the overall effectiveness of the clarification aids. • During April 1993 and October 1993 there were two additional occasions when the mine water discharge exceeded the discharge limits for total suspended solids. Increased retention time waz determined to be the key to settling out the suspended solids from the mine discharge water. The idle GSeam workings were, therefore, converted to a sump with approximately 22 to 30 acre-feet (7.0 to 10.0 million gallons) of live storage. The mine water collected in the B-Seam a transferred to the GSeam sump. The GSeam sump provides about 25 days retention time at the current mine inflow of about 200 gpm At the maximum projected inflow rate of 425 gpm, (refer to Section 2.04.7, Hydrology Description), the retention time a about 12 days. During the period from July 1993 through January 1994 OMI worked and negotiated with MSHA to obtain approval to use the idle GSeam workings az a sump. By letter dated February 8, 1994, MSHA granted approval to utilize the GSeam sump. The GSeam sump was operational by the end of February 1994. The chemical treattent system has been maintained and will be rued if necessary to effectively control suspended solids concentrations in mine discharge water. The water used to flood the area of the possible mine fire was decharged to the surface through temporary Sedimentation Pond E (initial rate approximately 200 gpm) or through the existing mine water discharge system (anticipated maximum rate 2,000 gpm), which includes the Sanborn Creek G Seam sump, associated c]azifier cells, and the surface mine water discharge pond, located west of the Sanborn Creek Mme portals. On completion of this discharge activity, Pond E was removed and associated disturbance areaz reclaimed. Analyse of discharge water quality. for initial discharges of water from the flooded mine workings in May 1999 through Cartfall 011 indicated acceptable water quality with slightly elevated TDS and iron, but with all values (full-suite including dissolved and acid- digested metals) within applicable effluent limits. While minor changes in runoff and mine dscharge water chemistry may occur az a result of mining and related operations, limited surface disturbance areas, corresponding limited disturbed area runoff volumes, and effective control of any necessary mine water discharge will minimize any potential for PR04 2.05-92 Revised August 2000