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Mountain Coal and Beaz Coal Water Quality Assessment CO-0038776 and CO-0044377 <br />The Mountain Coal WWTFs, via Outfalls 011, 012, 013 and 017, dischazge to WBID stream <br />segment COGUNF06, which means the Gunnison River Basin, North Fork of the Gunnison River <br />Sub-basin, Stream Segment 06. This segment is composed of "All tributaries to the North Fork of <br />the Gunnison River including lakes, reservoirs, and wetlands which aze not on national forest lands, <br />except for the specific listings in Segments 4, 5 and 7." Stream segment COGUNF06 is classified <br />for Warm Water Aquatic Life Class 2, Class lb Potential Primary Contact Recreation, Agriculture, <br />and Water Supply. <br />Numeric standards are developed on abasin-specific basis and are adopted for particular stream <br />segments by the Water Quality Control Commission. To simplify the listing ofthe segment-specific <br />standards, many of the aquatic life standards are contained in a table at the beginning of each chapter <br />of the regulations. The standazds in Table A-2 have been assigned to stream segment COGL1NF02 <br />and the standards in Table A-3 have been assigned to stream segment COGIJNF06 in accordance <br />with the Classifications and Numeric Standards for Gunnison and Lower Dolores River Basins. <br />It should be noted that for stream segment COGUNF06, standards for sulfate and dissolved iron and <br />a chronic standazd for dissolved manganese of 50 ug/1 are assigned only in the instance that the <br />receiving waters aze in actual use as a water supply. Based on available data, Sylvester Gulch, West <br />Sylvester Gulch, the Dry Fork of Minnesota Creek, and Lone Pine Gulch are not used as a water <br />supply and thus the standazds for these pollutants aze not applicable. Note that a chronic dissolved <br />•manganese aquatic life based standazd applies regardless. ~ ,- <br />Also for stream segment COGLlNF06, a temporary standard has been established for chronic <br />dissolved selenium based on existing quality. A value of 10.6 ug/1 was determined as the applicable <br />existing quality based on the Rationale for Classifications, Standards and Designations ofSegmenis <br />of the Gunnison and Lower Dolores River Basins. <br />standazds for metals are generally shown in the regulations as Table Value Standards (TVs), and <br />these often must be derived from equations that depend on the receiving stream hardness or species <br />of fish present. The Classification and Numeric standazds documents for each basin include a <br />specification for appropriate hardness values to be used. Specifically, the regulations state that: <br />The hazdness values used in calculating the appropriate metal standazd should be based <br />on the lower 95% confidence limit of the mean hazdness value at the periodic low flow <br />criteria as determined from a regression analysis of site-specific data. Where <br />insufficient site-specific data exists to define the mean hardness value at the periodic <br />low flow criteria, representative regional data shall be used to perform the regression <br />analysis. Where a regression analysis is not appropriate, asite-specific method should <br />be used. <br />Appendix A Page 4 of 20 Last Revised 3/9/2004 <br />