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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVlRONMEM, Water Qaaliry Contra[ Division <br />Rationale -Page 9. Permit No. CO-0000221 <br />Table V/~ -Effluent limitations jar Outja/l 008 <br /> Discharge Limitations <br /> Maximum Concerurations <br />Parameter 30-Day Avg. Daily Max. Rationale <br />Flow, MGD Report Repon Design Capacity <br />TSS, mg/P* 35 70 Federal Effluent Guidelines <br />Total Recoverable Iron, mg/P 1.0 Report Water Quality Standards <br />Settleable Solids, mP/P* Report 0.5 Federal Effluem Guidelines <br />Oil and Grease, mg/P Report 10 State EfjIuem Regulations <br />pH, s.u. (minimum-maximum) N/A 6.5-9.0 Water Quality Standards <br />WET, Chronic Lethality N/A No Statistical Srafe EJfluem Regulations <br /> Difference <br />Table VI-5 -Effluent Limitations for Outfall 009 <br /> Discharge Limitations <br /> Maximum .Concentrations <br />Parameter 30-Day Avg, Daily Max. Rationale <br />Flow, MGD Report Repon Design Capacity <br />TSS, mg/f ^ 35 70 Federal Ejjluem Guidelines <br />Total Iron, mg/P* 3.0 6.0 Federal Effluent Guidelines <br />Settleable Solids, mfJP* Report 0.5 Federal Effluent Guidelines <br />Oi! and Grease, mg/P Report 10 State Effluent Regulations <br />pH, s. u. (minimum-maximum) N/A 6.5-9.0 Water Quality Standards <br />* Total Suspended Solids and Total /ton limitations are Prirwry Limitations, and Settleable Solids limitations are <br />Alternate j-imitations. Exemption from these limitations due to storm evems is subject to burden of proof <br />requiremems -see section VI.A.3.b). <br />2. Total Maximum Daily Load (TMDLI Analysis IWarer Oualin Based Effluent Limitations/: Waxer quality standard <br />(WQS) based rota! recoverable iron [imitations apply to outfalls 004 and 008. In order to calculate WQS based <br />limitations, a Tora( A9aximum Dail}' Laad (fMDL) analysis ivas performed. In most situations, a mass balance <br />equation is used to determine the effluent concentrations that would not violate the allowable instream <br />concentrations defined by the water quality standards (except in the case ojpH, where the limitations are set directly <br />from stream standards or effluent regulations without using a mass balarsce approach). The mars balance equatio+: <br />is: <br />~ ly = McQr' MrQ~ <br />r <br />Q: <br />Where: <br />Q, = Upstream !ow flow (1 E3 or 30E3) from Table l11-2. <br />Q= = 30day average combined effluent flow for 11004 and 008 (highest momh from Table VI-8) <br />Q, = Combined downstream flox~ (Q, + Qr) <br />• Mr = Upstream background pollutam concentration from sec[ion 1!/.B.1. <br />Mr = UnAnown; Maximum allowable effluem pollutant concentration calculated using mars balance equation <br />M, = Maximum downstream allowable pollutant concemration (stream standard) <br />