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Mountain Coal Company 1999 Muual H)'drology Report West Elk Mine • 14SEHG Fault Inflow During WY99, as the downdip expression of the 14SEHG fault was mined through, the flow dried up and relocated to the downdip location. The flow at the end of WY99 was approximately 100 gpm. These locations aze identified on Map 1. Minor Inflows As is typical, MCC encountered small inflows during development mining with continuous miners. Initial inflows ranged from less than 0.05 gpm to 15 gpm, and then decreased to drips, or dried entirely. The locations of the inflows aze shown on Map 1. NW Panels Sealed Sump During WY99, MCC continued to utilize the NW Panels sealed sump, which is the area that was created by mining the 1 NW through 7NW longwall panels, and shown on Map 1. The use of this sump allowed MCC to become more efficient in handling mine inflows so as not to overload sedimentation ponds MB-1 and MB-2R, and to ensure that water is dischazged in compliance with MCC's CDPS discharge permit. MCC routed most of the mine inflow water to the NW Panels sealed sump. As pumping continued throughout WY99, the quality of the water from the Lone Pine pipeline has been good. There were no exceedances of the CDPS discharge limits or failures of the biomonitoring tests during WY99. • The NW Panels sealed sump was assumed to be full (about 375 acre-feet) during WY99, as MCC pumped water into the NW Panels sealed sump at about the same rate as water was pumped out of the sump. Samples of Mine Water Inflows During WY99, sampling of mine water inflows was hampered by the location of the inflows. The fault inflows occurred at low places in the mine floor, which allowed mixing of belt line water, process water, road maintenance (magnesium chloride application), and rock dusting operations to mix with the inflow water. Consequently, a representative sample of the inflows could not be obtained and the outflows from the mine via the Lone Pine Pipeline (discharge point 013) were the only mine water samples obtained during WY99. However, the quality of the inflows should not have changed since the major inflow event of January 1997. Mine Water Balance Figure 6 shows the mine water balance components for WY99. Inflows from the 14 SEHG fault and the B East Mains fault continued to have a significant impact on the mine water balance. North Fork diversions of 434 acre-feet were higher than in WY98, which is reasonable considering that mine production was higher. The total volume of water entering the mine from pond FW-1, inflows from the 14SEHG fault and the B East Mains fault, and other minor inflows • was approximately 657 acre-feet. 831-031.510 Page 20 Wright Water Engineers