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COLORADO DEPARTMENT OF HEALTH~ater Quality Comrol Division • <br />Rationale -Page 6, Permit No. CO-0029947 <br />VI. ' TERMS AND CONDITIONS OF PERM/T <br />A. Deterntinatian ojEjfluent Lititations <br />1. E/Ruem Limitations - The following Umiu will apply and are discussed in Sections Vl A.2, V/-A.3. <br />Table V! - 1- $,Q7trettt Zimitatlotu jar Otgja/la 001 and 002. <br />Patiuiiieter '': i ; :Llmitatton . :::: Ratrartale: " <br />Flow, MGD° Report Design Capacity <br />7SS, mg/C 30/45 Stott E(Jltrent Regulations <br />OU and Grease, mg/I° l0.0 State Efjlttent Regulations <br />pH, s. u.` 6 S - 9.0 Water Quality Standards <br />TDS mg/I' 2000 Salinity Regulations <br />WET, Acutt~ LCSO > 1005'o State Permit Regulations <br />= Monthly average/daily maxinwm <br />° =Daily maxinwm, if a visible sheen is observed, a grab sample shall be taken <br />= Daily minitnwn/daily maxinuun e„(jfuem limitation <br />° =Daily maximum <br />= Monthly average <br />2. Calculation of Water Oualuv Based Effluent Limitations <br />A mass balance equation was used to determine the effluent concentrations that would not violate the aUoxnble <br />in-stream concentrations defined by the rater quality standards (ucept in the case of pH, where flu Utnits are sd <br />directly from stream standards or ejjluem regulations without using a mass balance approach). The mass balance <br />equation is: <br />MaQa - M~Qi <br />M2 = <br />Qz <br />Where: <br />Q, = Upstream !ow flow (Q}~a/from Part IILB.2 <br />Q~ = Average daily effhtent flaw (design capacity) <br />Qj = Combined downstream flow (Q, + QtJ <br />M, = Upstream background pollutam concentration from I1LB.1 <br />Ms = Unbrown; Maximum aUoxable eBiuent pollutant concentration calculated using mass balance equation <br />Mt = Maximum downstream allowable pollutant concentration (stream standard) <br />Because of the mathematical relationship between flow, pollutant concentration and poUtuam mass, concentration <br />limitations calculated using this method implicitly limit instream pollutant mass to the maximum allowable level. <br />Also, only flow and concenttatiort Umitatians need to 6e specked M the permit. Mass Unutations arc not required. <br />A summary of the mass balance calculations that were evaluated arc shown and discussed in VLA.3.a. <br />