2022-09-29_PERMIT FILE - C1980007 (2)

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West Elk Mine • action. After evaluating many options, MCC concluded that the best alternative was to utilize the previously mined area as a large, underground sump while exploring additional treatment options. MCC's NPDES permit 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 guazantee 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 lazge capacity sumps became mandatory. An important factor in the decision to use the large capacity sumps for underground storage is the requirement that must operate the sedimentation ponds to maintain storage capacity for the foil run- off volume from the 10-year, 24-hour storm event. Thus, the operational capacity of the ponds to receive large mine dischazges is less 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 large volumes of flocculant produced. This colloid appears 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 standards 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-yeaz, 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. • 1.05-285 Revised June 1005 PRIG; Rev. March 1006; Rev. May 1006 PRIO