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Oxbow Mining WWTF Water Quality Assessment CO-0000132 <br />The Oxbow Mining, LLC W WTF is the sole known point source contributor to Sanborn Creek and <br />Elk Creek. No other point sources were identified as dischazgers to Sanborn Creek and Elk Creek <br />upstream or downstream. Thus, the findings of this assessment indicate that there is no dilution, no <br />other sources of pollutants of concern, and that assimilative capacities aze equal to the in-stream <br />standazds applied to the Oxbow Mining, LLC WWTF effluent discharges. <br />Information used in this assessment includes data gathered from Oxbow Mining, LLC, the WQCD, <br />the Colorado Division of Water Resources (DWR), ,the U.S. Census Bureau TIGER Mapping <br />Service, the U. S. Environmental Protection Agency (EPA), the U.S. Geological Survey (USGS), and <br />communications with the local water commissioner. The data used in the assessment consist of the <br />best information available at the time of preparation of this WQA package. <br />II. Water Quality <br />The Oxbow Mining, LLC WWTF discharges to the Water Body Identification (WBID) stream <br />segment COGUNF06, which means the Gunnison and Lower Dolores River Basins, North Fork of <br />the Gunnison River Sub-basin, Stream Segment 06. This segment is composed of the "All <br />tributaries to the North Fork of the Gunnison River including all lakes, reservoirs, and wetlands <br />which are not on national forest lands, except for the specific listings in Segments 4, 5 and ~." <br />Stream segment COGUNF06 is classified for Warm Water Aquatic Life Class 2, Class lb Potential <br />Primary Contact Recreation, Agriculnue, and Water Supply. <br />Numeric standazds are developed on abasin-specific basis and aze adopted for particular stream <br />segments by the Water Quality Control Commission. To simplify the listingofthesegment-specific <br />standazds, many of the aquatic life standazds 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 COGUNF06 in <br />accordance with the Classifications and Numeric Standards for Gunnison and LowerpoloresRiver <br />Basins. <br />standazds for metals aze generally shown in the regulations as Table Value standazds (TVs}, and <br />these oRen must be derived from equations that depend on the receiving stream hardness or species <br />of fish present. The Classification and Numeric Standards 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 standard should be based <br />on the lower 95% confidence limit ofthe mean hardness 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 hazdness 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 />Hardness data for Elk Creek near the point of the outfa11015 dischazge of the Oxbow Mining, LLC <br />W WTF were unavailable, however a mean hazdness value for segment 6 is specified in the WQCD <br />Document Rationale for Classifications, Standards and Designations of Segments of the Gunnison <br />Appendix A Page 3 of 10 Draft <br />