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Table A-7 <br />Low Flows for Cri le Creek at 0003 <br />Low Flow Amrual Jan Feb Maz Apr May Jun Jul Aug Sep Oct Nov Dec <br />(cfs <br />lE3 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 <br />Acute <br />30E3 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 <br />Chronic <br />Flow Continuity <br />As mentioned above, the flow of Arequa Gulch generally adds very little flow to Cripple Creek at critical low flow <br />times. CC&V asserts, based on observation, which Arequa Gulch does not flow into Cripple Creek or contribute to <br />the flow in Cripple Creek when Cripple Creek flows aze low. However, the data to support this lacks coincident <br />flow measurements. Measurements of Arequa Gulch (AG2.0) and Cripple Creek (0002 or 0003) were not taken <br />on the sane day. Never-the-less, WQCD does not dispute the conclusion that during critical low flow conditions, <br />Arequa Gulch generally contributes no surface flows to Cripple Creek, except in the case of very localized storm <br />events which would be very uncommon in the months of October and November, but more common in July. <br />IV. Technical Analysis <br />In-stream background data and low flows evaluated in Sections II and III aze ultimately used to determine the <br />assimilative capacity of Cripple Creek for pollutants of concern. A technical analysis of stream assimilative <br />capacity uses the annual low flow as calculated in the low flow analysis. <br />The mass-balance equation is used by the WQCD to calculate the maximum allowable concentration ofpollutants <br />in the effluent, and accounts for the upstream concentration of a pollutant at the existing quality, critical low flow <br />(minimal dilution), effluent flow and the water quality standazd. The mass-balance equation is expressed as: <br />Mz _ MaQ3-MiQi <br />Qz <br />where: <br />Q, = Upstreant low flow (lE3 or 30E3) <br />Qz = Dischazge design flow <br />Q3 =Downstream flow (Q~ + Qz) <br />M~ = In-stream background pollutant concentrations at the existing quality <br />Mz =Calculated maximum allowable effluent pollutant concentration <br />M3 = Maximwn allowable in-stream pollutant concentration (water quality standards) <br />Pollutants of Concern <br />The following metals were identified by the WQCD as pollutants of concern for this facility: <br />• Dissolved Aluminum <br />• Dissolved Cadmium <br />• Dissolved Copper <br />• Free Cyanide <br />• Total Recoverable Iron <br />• Dissolved Lead <br />• Dissolved Mangaziese <br />• Dissolved Nickel <br />• Dissolved Zinc <br />• Chlorine <br />Appendix A Page 9 of 13 <br />