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COLORADO DEPAR77LfENT OF PUBLIC HEALTH AND ENVIRONMEM, Water Quality Corurol Division <br />Rarionale -Page 1Q Permit No. CO-0000221 <br />The term MsQ~ represents the Total Maumum Daily Load (TMDL) of a pollutant that can be carried Iry the <br />receiving stream without violating the stream standards. The term MfQr represents the pollutant load that alr~ <br />exists iptream above the discharge palm in question. The difference between the two loads, which is MjQr - r <br />represems the loading that can be allocated to the discharge. <br />Ir may be appropriate in cenain situation to perform a more detailed analysis that would identify, quantify and <br />deveWp control strategies for additional individual pollutant source that might exist above and below the <br />permitree's discharge poims. !n this case, it was determined that limitation for these two discharge poims can be <br />calcu~atedrndependemly from any other polbuam source. However, the two outfalLs are couidered as one combined <br />source jar this purpose. <br />This rationale and accompanying permit serve n a Total Maximum Daily Load (TMDL) under Section 303(d) of the <br />Clean Water Act, and this 7MDL will be submitted to the US EPA Region VIII for review and approval. For this <br />jaciliry, total recoverable iron is the only parameter of concern. Values for efJluem flow are shown in Table VI-8 in <br />section V1.3.d)4) and low flows (30E3) are shown in Table /!/-2. /n this case, because the upstream background <br />concentration is significantly greater than the stream standard, the result is a negative number. The default is the <br />stream standard, which becomes the effluent limitation. <br />Table VI-6 -Summary of TMDL Based Mass Balance Calcularion <br />Upstream -: ; WQS/TMDUBhsed <br />Ambient Mean Stream Standard, _ Efjlumt.'Coitcentm_ tfon, <br />Period Coruentratian Chronic Chronic <br />(Ml) (M3) (M2) <br />Total Recoverable /ton. mz/f 6.77 1.0 -1.72 <br />Because of the mathematical relarionhip between Jlow, pollutant concentration and pollutant mats, concentra <br />limitation calculated using this method implicitly limit intream pollutam mass ro the maximum allowable lev <br />Also, only flow and concentration limitation need to be specified in the permit. Mass limitation are not required. <br />3. Discussion o(Effluent Limitation: The basis for the effluent limitation for TSS, pH and oil & grease is unchanged <br />from the previon permit. Please see previous rationale for the discussion. <br />a) Rerularions for Effluent Limitations: The Regulation for Effluent Limitation (10.1.0), apply to the convemional <br />pollutants. For this jaciliry the limitation for Oil and Grease are based on this regulation. <br />b) Annlicable Federal Effluent Guidelines and Standards: The federal guidelines which apply to this type of Jaciliry~ <br />are found under 40 CFR 434, titled Coal Mininr Point Source Effluent Guidelines. The limitations which apply <br />are: <br />Table VI-7 -Federal Standards (40 CFR 434) <br />Parameter <br />Limitations <br />30 Day Avg Daily Max. <br />pH, s. u. (minimum -maximum) ---6.0 - 9.0--- <br />Total Suspended Solids, mg/P• 35 70 <br />Total /ton, mg/P• <br />BAT** 3.5 7.0 <br />NSPS*** 3.0 6.0 <br />Settleable Solids, mP/P* N/A 0.5 <br />• 7hcsr pammrtrrz subjen ro Burden of Proof Rcquirrmtnn, see ncrr srnion <br />•• Btsr Availab(r Trthwtogy - app6'cs to rhosr ponds already consrrunrd <br />•'• Ntw Sourrr Prrjormancr Standards - appd'rs ro rhosr ponds consrruned afrrr 5/4/84 <br /> <br />