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Mountain Coal and Beaz Coal Water Oualitv Assessment CO-0038776 and CO-0044377 Because the low flow (Ql) for Sylvester Gulch, West Sylvester Gulch, the Dry Fork of Minnesota Creek and Lone Pine Gulch is zero, the assimilative capacities of these receiving streams for the pollutants of concern aze equal to the in-stream water quality standards. The upstream backgroundpollutant concentrations used in the mass-balance equation will varybased on the regulatory definition of existing ambient water quality. For most pollutants, existing quality is determined to be the 85a' percentile. For metals in the total recoverable form, existing quality is determined to be the SOei percentile. For pathogens such as fecal coliform, existing quality is determined to be the geometric mean. For non-conservative pazameters and ammonia, the mass-balance equation is not as applicable and thus other approaches are considered where appropriate. Note that conservative pollutants aze pollutants that aze modeled as if mass is conserved and there is no degradation, whereas non- conservativepollutants degade and sometimes aze created within a receiving stream depending on stream conditions. Amore detailed discussion of the technical analysis for these pazameters is provided in the pages that follow. Pollutants Evaluated The following pazameters were identified by the WQCD as pollutants to be evaluated for this facility: • Metals (Outfalls 004, 011, 012, 013, 016, and 017 for Mountain Coal; and' Outfa1100.1 for Bear Goal) • . Ammonia (Oritfall 004 for Mountain Coal) • Fecal Coliform (Outfall 004 for Mountain Coal) • Chlorine (Outfall 004 for Mountain Coal). During assessment of the facility, nearby facilities, and receiving stream water quality, no additional pazameters were identified as pollutants of concern. Mountain Coal Company: The Mountain Coal Company LLC, West Elk Mine is located in the NE 1/4, Section 16, T13S, R90W; 38° 55' 30" north latitude, 107° 2T 00" west longitude; approximately one mile east of Somerset, CO, on Highway 133 in Gunnison County. The long-term average reported design capacity of the none water discharges from Outfalls 004 and 016 to the North Fork of the Gunnison River is 0.142 MGD (0.22 cfs). Note that while this value is less than half of the long-term average determined using the facility's most recent data, it is used in later assimilative capacity calculations because it is expected to represent long term conditions. Note that this value includes effluent from the domesfic WWTF (Internal Outfa11007), with a design flow of 0.0105 MGD (0.016 cfs), which is combined in Pond MB-2R with other sources and dischazged to the North Fork of the Gunnison River via Outfa11004. Wastewater treatment is accomplished using non-aerated lagoons and sedimentation in underground sumps. The technical analyses that follow for discharges to the North Fork of the Gunnison River include assessments of the assimilative capacity based on the total combined design capacity that includes Bear Coal Company's Outfa11001 as discussed below. Appendix A Page 12 of 20 Last Revised 3/9/2004