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West Elk Mine • East Mains fault and east of the IONE Tailgate entries to provide temporary storage while sufficient pumping and pipeline capacity was constructed to remove the water from the mine. Even after developed the capability to pump the unexpected groundwater inflows to the surface, these flows overwhelmed the hydraulic capacity of the treatment processes in the sedimentation ponds. A complicating factor was that water pumped from the NE Tailgate sump caused "treatabiliry" problems (see previous Mine Water Treatment discussions), To assure the safety of its workforce and to continue with mining operations, it was necessary for MCC to take decisive action. After evaluating many options, MCC concluded that the best alternative was to utilize the previously mined azea as a large, underground sump while exploring additional treatment options. MCC's NPDES pemut for the sedimentation ponds has a stringent daily maximum daily limit for total suspended solids (TSS) of 70 mg/L (35 mg/L on a 30-day average basis). Historically, has met this limit with few exceptions. The sedimentation ponds were designed and operated to accommodate the volume of water that has traditionally been discharged from the mine (i.e., dominated by imported water). With the unprecedented groundwater inflows with the unusual colloid in 1996, MCC experienced considerable difficulty complying with the effluent limit for TSS. In November, 1996, MCC received a letter from the Colorado Water Quality Control Division (CWQCD) which summarized the permit exceedances in 1996 and potential enforcement actions that could be taken if additional exceedances occurred from inflows from the B East Mains fault or the projected extension of the fault in the Box Canyon Mains entries. The only practical way to guarantee that the hydraulic capacity of the system was not exceeded was to create storage capacity. Because surface storage sites with sufficient volume are not available within or near the • mine facilities azea, the in-mine use of the large capacity sumps became mandatory. An important factor in the decision to use the lazge capacity sumps for underground storage is the requirement that must operate the sedimentation ponds to maintain storage capacity for the full run- off volume from the 10-yeaz, 24-hour storm event. Thus, the operational capacity of the ponds to receive lazge mine dischazges is Tess than the physical capacity of the ponds. Compounding the problem of increased inflows to the sedimentation ponds was the presence of an unusual suspended colloid which had not been previously encountered. This colloid did not lend itself to sedimentation utilizing the flocculants/polymers that had historically been effective. Although MCC was successful in treating this colloid by applying heavy doses of alum, this is not a practicable long-term solution due to the lazge volumes of flocculant produced. This colloid appeazs to have been picked up while flowing across the mine floor, or while stored in the NE Tailgate or other sumps where the water is exposed to the coal and parting material. Water quality analysis on samples taken directly from the fault show the water to be of sufficient quality to meet NPDES discharge standazds for the North Fork. In short, MCC concluded that there was no alternative but to utilize the NW Panels sealed sump in 1996 in order to: (1) avoid hydraulic overloading of the treatment facility, (2) maintain the required capacity to store run-off from the 10-year, 24-hour storm event in the ponds, and (3) provide the necessary sedimentation pond residence time to remove the colloids and other constituents to levels that would enable NPDES permit compliance. After the NE and Box • Canyon Panels have been mined, MCC also plans to utilize these mined-out areas as large capacity sumps. 2.05-145 Revised November 2004 PR/0