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Trapper Mining, Inc. WWTF Water Quality Assessment CO-0032115 <br />Table A-3 <br />Low Flows for Johnson Gulch, No Name Gulch, Far East Buzzard Gulch, Coyote <br />Gulch, Ute Gulch, Middle Pyeatt Gulch, East Pyeatt Gulch, West Pyeatt Gulch, Deer <br />Gulch, Grouse Gulch, Sage Gulch, Oak Gulch, Horse Gulch, West Horse Gulch, West <br />Flume Gulch, Middle Flume Gulch, East Middle Flume Gulch, East Flume Gulch, Deal <br />Gulch at the Tra er Minin ,Inc. WWTF <br />_~ <br />Lo/w/ ((F~+l+ow Annua! San Feb i)lar k Apr May :lun Ju! rlug ; Sep ,;°Uct. ,Nov ~ k~eC <br />lE3 0 .0 0 0 0 0 0 0 0 0 0 0 0 <br />Acute <br />30E3 0 0 0 0 0 0 0 0 0 0 0 0 0 <br />G7uonic <br />N. Technical Analysis <br />In-stream background data and low flows evaluated in Sections II and III aze ultimately used to <br />determine the assimilative capacity of Johnson Gulch, No Name Gulch, Faz East Buzzard Gulch, <br />Coyote Gulch, Ute Gulch, Middle Pyeatt Gulch, East Pyeatt Gulch, West Pyeatt Gulch, Deer Gulch, <br />Grouse Gulch, Sage Gulch, Oak Gulch, Horse Gulch, West Horse Gulch, West Flume Gulch, Middle <br />Flume Gulch, East Middle Flume Gulch, East Flume Gulch, and Deal Gulch neaz the Trapper <br />Mining, Inc. WWTF' for pollutants of concern. For all parameters except ammonia, it is the <br />WQCD's approach to conduct a technical analysis of stream assimilation capacity using the lowest <br />of the monthly ]ow flows (referred to as the annual low flow) as calculated in the low flow analysis. <br />For ammonia, it is the standard procedure ofthe WQCD to determine assimilative capacities for each <br />month using the monthly low flows calcu]ated in the low flow analysis, as the regulations allow the <br />use of seasonal flows when establishing assimilative capacities. <br />The WQCD's standard 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 standard. The mass-balance equation is expressed as: <br />Mz _ M3Q3-M~Qi <br />Qz - <br />Where, <br />Qi =Upstream low flow (lE3 or 30E3) <br />Q1=Average daily effluent flow (design capacity) <br />Q3 = Downsveam flow (QI + QZ) <br />M~ = In-stream background pollutant concentrations at the existing quality <br />1LI1=Calculated maximum allowable effluent pollutant concentration <br />M3 =Maximum allowable in-stream pollutant concentration (water quality standards) <br />When Q~ equals zero, QZ equals Q3, and the following results: <br />Appendix A Page 5 of 8 Draft <br />