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West Elk Mine 2002 Annual Hydrology Report • 4.3 Sedimentation Ponds There are 7 sediment ponds at the Project utilized to manage mine water, storm water runoff, and wastewater treatment effluent. All ponds but MB-5, MB-3 and re lined to prevent seepage. There is also a "freshwater" pond (FW-1) that is used to equalize diversions from the North Fork and provide storage. Pond FW-1 serves as the raw fresh water supply for the mine's domestic water use and in-mine water needs. In WY2002, two ponds discharged water to the North Fork, pond MB-2R (41 ac-ft), and ponds MB-3, 4, and 5 (collectively about 0.6 ac-ft). Ponds MB-1, RPE, SG- 1, and FW-1 had no discharge in WY2002. Table 9 summarizes the water quality of all CDPS discharges, including sedimentation pond (SG-1), for WY-2002. Table 10 shows the CPDS discharge limitation values for the sediment ponds. Figure 3 illustrates the mine water balance including the pond discharges. Table 10 Summary of Sediment Pond CDPS Discharge Limits Parameter and Time Period Sedimentation Pond Discharge Limits TSS (mg/1) • 30-Day Average 35 • 7-day average n.a. • Maximum ~0 TDS (mg/I) • 30-Day Average n.a. • 7-day average n.a. • Maximum Report Oil and Grease (1) • 30-Day Average No Sheen • 7-day average No Sheen • Maximum No Sheen To[al Iron (mg/1) • 30-Day Average 3.5 • 7-day average n.a. • Maximum 7~0 pH (S.U.) • 30-Day Average 6.5-9.0 • 7-day average 6.5-9.0. • Maximum 6.5-9.0 1) No Sheen or less than 10 mg/I 4.3.1 Ponds MB-1 and MB-2R Pond MB-1 collects the Project's surface operations water and diverted stormwater runoff. MB-1 can be discharged to either the North Fork or pond FW-1. Pond MB-2R receives surface operations • water, storm runoff, and effluent from the WWTP. Discharge from MB-2R is typically routed to the North Fork, but can be diverted to FW-1, if necessary. Both MB-1 and MB-2R retain water so Project # 00301 21 HydroGeo, Inc.