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Snowcap Coal Co. Inc WWTF Water Quality Assessment CO-0027146 <br />The WQCD's standazd analysis consists of steady-state, mass-balance calculations for most <br />pollutants and modeling for pollutants such as ammonia. The mass-balance equation is used by the <br />WQCD to calculate the maximum allowable concentration ofpollutants in the effluent, and accounts <br />for the upstream concentration of a pollutant at the existing quality, critical low flow (minimal <br />dilution), effluent flow and the water quality standazd. The mass-balance equation is expressed as: <br />Mz _ M3Q3 -MiQi <br />Qz <br />Where, <br />Q~ =Upstream low flow (lE3 or 30E3) <br />Qi =Average daily effluent flow (design capacity) <br />Qi =Downstream flow (Q~ + Q2) <br />M~ = In-stream background pollutant concentrations at the existing quality <br />M2 =Calculated maximum allowable effluent pollutant concentration <br />M3 =Maximum allowable in-stream pollutant concentration (water quality standazds) <br />The upstream background pollutant concentrations used in the mass-balance equation will varybased <br />on the regulatory definition of existing ambient water quality. For most pollutants, existing quality is <br />deternned to be the 85~' percentile. For metals in the total recoverable form, existing quality is <br />determined to be the 50`" percentile. For pathogens such as fecal coliform, existing quality is <br />determined to be the geometric mean. <br />For non-conservative parameters and ammonia, the mass-balance equation is not as applicable and <br />thus other approaches aze considered where appropriate. Note that conservative pollutants aze <br />pollutants that are modeled as if mass is conserved and there is no degradation, whereas non- <br />conservativepollutants degrade and sometimes aze created within a receiving stream depending on <br />stream conditions. Amore detailed discussion of the technical analysis for these pazameters is <br />provided in the pages that follow. <br />Pollutants Evaluated <br />The following parameters were identified by the WQCD as pollutants to be evaluated for this <br />facility: <br />• Arsenic <br />• Cadmium <br />• Copper <br />• Chromium <br />• Iron <br />• Lead <br />• Manganese <br />• Mercury <br />• Nickel <br />• Selenium <br />• Silver <br />• Zinc. <br />Appendix A Page 8 of 12 Last Revised 9/15/2003 <br />