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Mountain Coal Company 1998 Annual Hydrology Report Wes( Elk Mine Sedimentation Ponds There are seven ponds, MB-1, MB-2R, MB-3, MB-4, MB-5, RPE pond, and SG-1, at the West Elk Mine that are utilized to manage mine outflows, stormwater runoff, and wastewater treatment effluent. In addition, there is a "freshwater" pond, FW-], that is used to equalize diversions from the North Fork. Pond FW-1 serves as the raw water supply for the mine for both domestic and in-mine purposes. In WY98, ponds MB-1 and MB-2R dischazged about 300 acre- feet to the North Fork, whereas ponds MB-3 and MB-5 together discharged less than one acre- foot. Pond MB-4 did not discharge during WY98. Pond SG-1, iocated in Sylvester Gulch, was operational for the first time and discharged approximately 8 acre-feet during WY98. The pond receives runoff from the ventilation shafts area and water encountered during development of the mine ventilation shafts. The RPE pond, also in operation for the first time in WY98, did not discharge during WY98. Ponds MB-1 and MB-2R As depicted in Figure 6, ponds MB-1 and MB-2R play a strategic role in water management at the mine. Pond MB-1 receives mine dischazges and stormwater runoff, and can be dischazged to either the North Fork or transferred to pond FW-l. Pond MB-2R receives mine discharges, stormwater runoff and effluent from the wastewater treatment plant (WWTP), and is released to the North Fork or occasionally sent to pond FW-1. Both ponds operate in a "batch" mode; i.e. water is detained while settling occurs then discharged to the North Fork. Pond MB-1 was re-lined with a HDPE liner in January 1998 to eliminate a suspected source of water to the mine site landslide. It was believed that the previous liner was damaged, thereby • allowing water to seep out of the pond and to contribute inflow to the mine site landslide. The new liner has been extremely effective in eliminating seepage from MB-1, which, in rum, has aided in stabilizing the landslide. Pond discharges to the North Fork are made in accordance with the MCC CDPS Discharge Permit No. CO-0038776. Table 8 summarizes the water chemistry of ponds MB-1 and MB-2R discharges during WY97. Table 9 provides the numeric discharge limits for the sedimentation ponds, as per the CDPS permit. Neither pond had a discharge that exceeded numeric standards during WY98. Use of the NW Panels sealed sump and the Lone Pipe pipeline resulted in improved water management in sedimentation ponds MB-1 and MB-2R. This fact is evident by the reduced volume of water treated in the ponds and the lack of discharge exceedences. The water quality of the North Fork is better protected during upset conditions due to the storage capacity of the NW Panels sealed sump Ponds MB-3 and MB-5 During WY98, ponds MB-3 and MB-5 dischazged a total of less than one acre-foot to the North Fork. These dischazges were made in accordance with the MCC CDPS permit. Pond MB-5 received exclusively stormwater runoff and pond MB-3 received runoff as well as washdown water from conveyors and the silos. All relevant numeric dischazge limits were met. -031.500 Pagel Wrig 1 Warer Engineers