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Pittsburg and Midway Coal Company Edna Mine Water Quality Assessment CO-0032638 <br />mine water discharge as it would be impractical to account for the treated mine water discharges <br />without assessing the surface runoffflow and its associated constituents that are commingled prior to <br />discharge. <br />Based on available information, the unnamed tributary to Trout Creek had a low flow of zero. <br />Outfall 004 is the sole known point source contributor to the unnamed tributary to Trout Creek. No <br />other point sources were identified as dischargers to the unnamed tributary to Trout Creek upstream <br />or downstream of the confluence with Trout Creek. Thus, the findings of this assessment indicate <br />that there is no dilution, no other sources of pollutants of concern, and that assimilative capacities are <br />equal to the in-stream standards applied to Outfa11004. <br />For Outfall 007, the ratio of the in-stream low flow to the design flow is 0.064:1. The nearest <br />upstream and downstream discharges had no impact on the assimilative capacities available to the <br />Edna Mine Outfall 007. However, due to the small available dilution, analyses indicate that <br />assimilative capacities are relatively limited. <br />Information used in this assessment includes data gathered from the Edna Mine, the Division, the <br />Annual Hydrology Reports submitted to the Colorado Division ofMinerals and Geology (CDMG), <br />the U.S. Environmental Protection Agency (EPA}, the U.S. Geological Survey (USGS), and the U.S. <br />Census Bureau. The data used in the assessment consist of the best information available at the time <br />of preparation of this WQA. <br />II. Water Quality <br />The Edna Mine dischazges to the Water Body Identification (WBID) stream segment COUCYA13c, <br />which means the Upper Colorado River Basin, Yampa River Sub-basin, Stream Segment 13c. This <br />segment is composed of the "Mainstem of Trout Creek from headgate of Spruce Hill Ditch <br />(approximately 2,500 feet north of where County Road 27 crosses Trout Creek) to its confluence <br />with Fish Creek. All tributaries to Trout Creek from the headgate of Spruce Hill Ditch <br />(approximately 2,500 feet north of where County Road 27 crosses Trout Creek) to County Road <br />179." Stream segment COUCYA13c is classified for Cold Water Aquatic Life Class 1, Class la <br />Existing Primary Contact Recreation, Agriculture and Water Supply (June through February only}. <br />Numeric standazds are developed on abasin-specific basis and are adopted for particular stream <br />segments by the W ater Quality Control Commission. To simplify the listing ofthesegment-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 standards in Table A-2 have been assigned to stream segment COUCYA13c <br />in accordance with the Classifications and Numeric Standards for Upper Colorado RiverBasin and <br />North Platte River (Planning Region I2). <br />Appendix A ~wQn nv vers;on as FnsL> Page 3 of 19 Last Revised September Z, 2005 <br />