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Snowcap Coal Co. Inc WWTF Water Quality Assessment CO-0027146 <br />II. Water Quality <br />The Snowcap WWTF dischazges to the Water Body Identification (WBID) stream segment <br />COLCLC02, which means the Lower Colorado River Basin, Lower Colorado River Sub-basin, <br />Stream Segment 02. This segment is composed of the "Mainstem of Colorado River from <br />immediatelybelowthe confluence with Pazachute Creek to immediately above the confluence of the <br />Gunnison River." Stream segment COLCLC02 is classified for Warm Water Aquatic Life Class 1, <br />Class la Existing Primary Contact Recreation, Agriculture, and Water Supply. <br />Numeric standazds aze developed on abasin-specific basis and aze adopted for particular stream <br />segments by the Water Quality Control Commission. To simplify the listing ofthesegment-specific <br />standazds, many of the aquatic life standards aze contained in a table at the beginning of each chapter <br />ofthe regulations. The standards in Table A-2 have been assigned to stream segment COLCLC02 in <br />accordance with the Classif cations and Numeric Standards for Lower Colorado River Basin. <br />Standards for metals aze generally shown in the regulations as Table Value standazds (TVS), and <br />these often must be derived from equations that depend on the receiving stream hazdness or species <br />of fish present. The Classification and Numeric standazds documents for each basin include a <br />specification for appropriate hazdness 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 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 />A regression analysis was conducted using data from USGS gage station 09095500 combined with <br />data from Riverwatch station 552, which is at the same location, approximately 3 miles upstream of <br />the Snowcap W WTF. There were 117 paired flow and hardness data points available. However, 43 <br />were excluded due to their representation of high flow conditions. The remaining 74 were used in <br />the completion of a regression analysis to a low flow of 1380 cfs, which was the lowest of the <br />measured flows in the data set. The 95'" confidence interval was then calculated, resulting in a <br />hardness value equal to 257 mg/1. This hardness value and the formulas contained in the TVS were <br />used to calculate the in-stream water quality standazds for metals with the results shown in Table A- <br />Ambient Water Ouality <br />The WQCD evaluates ambient water qualitybased on a variety of statistical methods as prescribed in <br />Section 31.8(2)(a)(i) and 31.8(2)(b)(i)(B) of the Colorado Department of Public Health and <br />Environment Water Quality Control Commission Regulation No. 31. Ambient water quality is <br />evaluated in this WQA for use in determining assimilative capacities and in completing <br />antidegradation reviews for pollutants of concern. <br />J <br />Appendix A Page 3 of 12 Last Revised 9/15/2003 <br />