2008-03-21_PERMIT FILE - C1980007A (46)

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West Elk Mine • Sedimentation Ponds Management The fresh water pond (FW-1) receives North Fork water from the raw water intake gallery. From FW-1, water is either diverted to the water treatment plant for domestic purposes or it is conveyed to a 1.2 million gallon raw water storage tank that is located to the south of the main mine facilities and west of the Sylvester Gulch Facilities Area. Water is then used for both longwall mining operations and continuous miner/development mining operations. Within the mine, water is used for dust suppression and for the hydraulic equipment associated with the longwall and continuous miners. Of the five sedimentation ponds, three ponds (MB-3, MB-4, and MB-5) receive only local runoff and water from facilities washdown operations. In contrast, MB-I and MB-2R can receive mine water dischazge, in addition to local runoff. Consequently, Ponds MB-1 and MB-2R have the largest capacities at 13.3 and 14.6 acre-feet, respectively, and are the focus of the remaining discussion. Prior to the Mine Water Pumping Facility (MWPF) coming online in 2000, Ponds MB-1 and MB-2R received most of the mine water. While they no longer receive significant volumes of mine water, the ponds continue to play a pivotal role in surface water management at West Elk Mine. The waters are treated and then dischazged to the North Fork, in accordance with the NPDES permit that is provided as Exhibit 7. The combined volume of these ponds is 27.9 acre-feet. Because the ponds also intercept stormwater and snowmelt runoff, • the optimal mode of pond operations is to keep the pond levels low to maintain the 10-year return frequency, 24-hour duration runoff volume of 6.8 acre-feet for both ponds. One of the major reasons MCC utilized the NW Panels sealed sump in late 1996 was to assure that there would be sufficient storage capacity in Ponds MB-1 and MB-2R to treat the necessazy stormwater volumes. Mine Water Discharges MCC has added the capability to discharge water from the NW Panels sealed sump into Lone Pine Gulch. MCC received approval from the CWQCD to add this location as an NPDES dischazge point (Outfall #013). Discharge to Lone Pine Gulch began in late December 1997. Long-term observations of Lone Pine Gulch by MCC staff indicate that it is an ephemeral drainage, which flows only in response to snowmelt runoff and intense rainfall runoff events. The maximum flow rate that can be pumped to Lone Pine Gulch is 2,000 gpm, but has typically been approximately 300 gpm. The dischazge point is very low in the watershed, approximately 300 feet upstream of the confluence with the North Fork where the drainage flattens out. Since MCC began pumping from the NW Panels sealed sump into Lone Pine Gulch, the water quality has met NPDES standazds without further treatment. Discharges via the Lone Pine facility ceased in 2000, following the completion of the connection of the NW Panels sealed sump to the NE Panels sealed sump. Once the connection was established, mine water was pumped to the surface for discharge to Sylvester Gulch. 2.05-221 Revised November 2004 PR/0; Rev. March 2006; Rev. May 1006 PRIO