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Oxbow Mining W WTF Water Quality Assessment CO-0000132 <br />Oxbow Mining, LLC mine water dischazge goes to Elk Creek, the Mountain Coal Company <br />discharges are not expected to impact assimilative capacities. <br />Bear Coal Company, Inc. (CO-0044377): The Bear Coal Company, Inc. BeazNo. 3 Mine is a <br />reclaimed coal mine with one mine water discharge. This facility is located in the SE '/<, <br />Section 8, T13S, R90W; 38° 55' 40"north latitude, 107° 27' 44" westlongitude; on Highway <br />133, southwest of Somerset, CO in Gunnison County.. Bear Coal Company's outfall 001 <br />discharges mine water to the North Fork of the Gunnison River. Because Oxbow Mining, <br />LLC mine water dischazge goes to Elk Creek, the Beaz Coal Company discharge is not <br />expected to impact assimilative capacities. <br />Two other coal mining facilities, the Minrec-Blue Ribbon Mine (COG-850009) and the. <br />Bowie Resources, Ltd. Bowie No. 1 East and No. l West Mines (formerly CO-0033685, now <br />COG-850043) dischazge surface nmoffwaterto tributaries to theNorthFork ofthe Gunnison <br />River a few miles downstream in Delta County, However, as previously stated, surface <br />runoff discharges are not considered to impact the assimilative capacities because these <br />discharges do not occur during periods of critical low flow, thus these facilities aze not <br />considered in this assessment. Additionally, the Bowie Resources, Ltd. Bowie No. 2 Mine <br />(CO-0044776) dischazges mine water and surface runoff water to tributaries to the North <br />Fork of the Gunnison River more than 5 miles downstream. However, the assimilative <br />capacity calculations were not affected by downstream contributions from the Bowie <br />Resources, Ltd. Bowie No. 2 Mine WWTF as discussed below. <br />Due to the low flow of zero, consideration of other sources when allocating assimilative capacities to <br />dischazges to Sanborn Creek and Elk Creek was not necessary because the full assimilative <br />capacities of these receiving streams aze equal to the stream standazds. <br />Based on available information, there is no indication that non-point sources were a significant <br />source ofpollutants of concern. Thus, non-point sources were not considered in this assessment. <br />Chlorine: The mass-balance equation was used to determine the assimilative capacity for chlorine. <br />There are no point sources discharging total residual chlorine within one mile ofthe Oxbow Mining, <br />LLC outfall 018. Because chlorine is rapidly oxidized, in-stream levels of residual chlorine aze <br />detected only for a short distance below a source. Ambient chlorine was therefore assumed to be <br />zero. <br />Using the mass-balance equation provided in the beginning of Section IV, the acute and chronic low <br />flows set out in Section III, the chlorine background concentration of zero as discussed above, and <br />the in-stream standazds for chlorine shown in Section II, assimilative capacities for chlorine were <br />calculated. The data used and the resulting calculations of the allowable discharge concentration, <br />M1, are set forth below. <br />Parameter Q~ (cfs) QZ (cfs) Qs (cfs) M~ (mg/1) M3 (mg/I) M2 (mg/1) <br />Acute Chlorine 0 0.075 0.075 0 0.019 0.019 <br />Chronic Chlorine 0 0.075 0.075 0 0.011 O.Oll <br />Appendix A Page 8 of 10 Draft <br />