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Mountain Coal and Beaz Coal Water Quality Assessment CO-0038776 and CO-0044377 <br />Because the low flow (QI) for Sylvester Gulch, West Sylvester Gulch, the Dry Fork of Minnesota <br />Creek and Lone Pine Gulch is zero, the assimilative capacities of these receiving streams for the <br />pollutants of concern aze equal to the in-stream water quality standards. <br />The upstream background pollutant concentrations used in the mass-balance equation will vary based <br />on the regulatory definition of existing ambient water quality. For most pollutants, existing quality is <br />determined to be the 85a' percentile. For metals in the total recoverable fonn, existing quality is <br />determined to be the SOa' percentile. For pathogens such as fecal coliform, existing quality is <br />determined to be the geometric mean. <br />For non-conservative pazameters and ammonia, the mass-balance equation is not as applicable and <br />thus other approaches aze considered where appropriate. Note that conservative pollutants aze <br />pollutants that are modeled as if mass is conserved and there is no degradation, whereas non- <br />conservativepollutants degrade and sometimes aze created within a receiving stream depending on <br />stream conditions. Amore detailed discussion of the technical analysis for these pazameters is <br />provided in the pages that follow. <br />Pollutants Evaluated <br />The following parameters were identified by the WQCD as pollutants to be evaluated for this <br />facility: <br />• Metals (Outfalls 004, Ol 1, 012, 013, 016, and 017 for Mountain Coal; and' Outfa11001 for <br />. Bear Goal) <br />• ~ Ammonia (Oritfall 004 for Mountain Coal) <br />• Fecal Coliform (Outfa11004 for Mountain Coal) <br />• Chlorine (Outfa11004 for Mountain Coal). <br />During assessment ofthe facility, nearby facilities, and receiving stream water quality, no additional <br />pazameters were identified as pollutants of concern. <br />Mountain Coal Company: The Mountain Coal Company LLC, West Elk Mine is located in the NE <br />1/4, Section 16, T13S, R90W; 38° 55' 30" north latitude,107° 27' 00" west longitude; approximately <br />one mile east of Somerset, CO, on Highway 133 in Gunnison County. The long-term average <br />reported design capacity of the mine water dischazges from Outfalls 004 and 016 to the North Fork <br />of the Gunnison River is 0.142 MGD (0.22 cfs). Note that while this value is less than half of the <br />long-term average determined using the facility's most recent data, it is used in later assimilative <br />capacity calculations because it is expected to represent long term conditions. Note that this value <br />includes effluent from the domestic WWTF (Internal Outfa11007), with a design flow of 0.0105 <br />MGD (0.016 cfs), which is combined in Pond MB-2R with other sources and dischazged to the North <br />Fork of the Gunnison River via Outfall 004. <br />Wastewater treatment is accomplished using non-aerated lagoons and sedimentation in underground <br />sumps. The technical analyses that follow for discharges to the North Fork of the Gunnison River <br />include assessments of the assirnila6ve capacity based on the total combined design capacity that <br />includes Beaz Coal Company's Outfa11001 as discussed below. <br />Appendix A Page 12 of 20 Last Revised 3/9/2004 <br />