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~~' <br />COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division <br />Rationale, Page 8 Permit No. CO-0026981 <br />APPENDIX A <br />Mass Balance Equation for Calculating WQS-Based Effluent Limits <br />WQS CQ7-10 + Qeff) - (Q7-10 X Camb) <br />Ceff = <br />Qeff <br />Where: <br />Ceff = Calculated effluent concentration <br />WQS = Applicable water quality standard <br />Q7-10 =Receiving water 7-day, 10-year low flow <br />(See previous discussion for values), cfs <br />Qeff = Discharge Design Flow, <br />(See previous discussion for values), cfs <br />Camb = Ambient instream concentration, mg/1 <br />i (See below in calculations) Example: 0.00029 mg/1 for Cd <br />Below is the 30-day average limit calculation for the applicable metal <br />parameters. <br />EL (TR Cd) = 0.0018 (1.5 + 2.7} - 0.00029 (2.7) = 0.0045 mg/1 <br />1.5 November through April <br />EL (TR Cd) = 0.0018 (1.3 + 6.3) - 0.00093 (6.3) = 0.0060 mg/1 <br />1.3 May through July <br />EL (TR Cd) = 0.0018 (3.5 + 3.9) - 0.0010 (3.9) = 0.0027 mg/1 <br />3.5 August through October <br />EL (TR Cu) = 0.023 (1.5 + 2.7) - 0.0095 (2.7) = 0.047 mg/1 <br />1.5 November through April <br />EL (TR Cu) = 0.023 (1.3 + 6.3) - 0.0044 (6.3) = 0.11 mg11 <br />1.3 May through July <br />EL (TR Cu) = 0.023 (3.5 + 3.9) - 0.017 (3.9) = 0.030 mg/1 <br />3.5 August through October <br />