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

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West Elk Mine Sanitary Wastewater -West Elk Mine has apackage-type wastewater treatment plant to treat sewage (primarily shower water) from the mine's facilities. The plant, constructed in 1982, has a designed throughput of 10,000 gallons per day. With an aeration basin and clazifier, the plant provides primazy and secondary treatment. The wastewater treatment plant is operated under applicable state laws that govern wastewater treatment facilities, administrated by the CDPHE. In 1996, MCC expanded the plant to increase the throughput to 20,000 gpd. The expansion included a 3,000 gallon flow equalization tank, an additional clarifier and a flocculent system. The clarifier is added to provide additional retention and clarification as a passive safeguard to plant operation. The flocculent system will be used as a secondary safeguard that may be operated to entrance solids settling in the primary clarifier. Runoff from Disturbed Areas -Overland runoff, which passes over disturbed areas within the permit area, is channeled to one of the sedimentation ponds. Sediment pond water may be discharged to the North Fork or stored when water rights are in priority for reuse within the mine azea, The quantity of effluent discharged from the sedimentation ponds is described in the quarterly NPDES discharge monitoring reports and in the Annual Hydrology Reports. Underground Water Management Historically (prior to 1996), mine process water runoff and groundwater inflows flowed down- dip in the B Seam workings, and were collected in various sized open sumps, pumped to the sump at the bottom of the slopes, and then pumped to one of the sedimentation ponds on the surface (MB-1 or MB-2R). After the water daylighted at the mine portals, a chemical coagulant and/or flocculent was added to the flow prior to entering the sedimentation ponds. After typical residence times of a few days, the pond water was dischazged in accordance with MCC's NPDES permit. Prior to 1996, MCC had a strong history of NPDES permit compliance. Two key events occurred in 1996 that caused MCC to alter this historic practice. The first was the unprecedented inflows from the BEM fault. The second was the presence of a new colloid in the mine water that would not settle out in the ponds. As a result of these events, MCC changed both the way it manages water underground and the way it treats the water. The current mine water management practices (as of 2004) are shown schematically in Figure 22. In general, the schematic represents three key components: mine inflows, mine outflows, and in-mine water transfers. In order to better keep track of the quantities of water coming into the mine, leaving the mine, and being stored in the various sealed sumps, MCC has installed and will install numerous totalizing flow meters. These flow meters will enable a more accurate computation of the mine water balance, Mine Inflows -Mine inflows consist of imported water from the North Fork for mining uses, various, smaller groundwater inflows, and significant groundwater inflows, such as the BEM and 14HG faults. The large groundwater inflows aze shown sepazately since they require special management. Estimates for the various mine inflows for 2002, for instance, are as follows: r1 U 2.05-226 Revised November 2004 PRl0; Rev. March 2006; Rev. May 2006 PRl0