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COLORADO DEPARTMENT OF HEALTH, Waxer Quality Control Division Rationale -Page 13, Permit No. CO-0034142 2. Calculation of Waxer Oualirv Based Effluent Limitations A mass balance equation Kos used to daerntine the effltteN rnncentrations that xnu/d not violate the allowable in-stream concuurations defined by the xnttr quality standards (ezctpt in the case of pH, where the limits are set directly from stream standards or effluent regutations without using a mass balance approach). The mass balance equation is: - Mt = M1Q~ - MiQt Qz Where: _ Qt = Upstream !ow flow (]E3 or 30E3J from Part I/I. B.2 Qz = Average daily effluent flow (design capacity) Qt = Combined downstream flow (Qt + QzJ Mt = Upstream background pollutant concentration from III.B. l Mz = Unbtown; Maximum allowable eBluent poflutam conceuration calculated using mass balance equation Mt = Maximwn downstream allowable pollutant concentration (stream standard) Because of the mathematical relationship between lbw, pollutant concentration and pollutant mass, concentration limitations calculated using this method implicitly limit inrtream Pollutant mass to the maximum albwable Itve[. Also, Doty flow and concentration limitations need to be specified in the permit. Mass limitations are not required. A summary of the mass balance calculations (if mryJ are shown and discussed in VJ.A.3. 3. Discussion of E, jfluent Limitations a. Regulations (or Effluent Limitations: The Regulations for Effluent Limitations (10.1.0), apply to the conventional pollutants. For this facifiry, as was done in the previous permit, the limitations for BODs, 7SS, Total Residual Chlorine, and Oil atul Grease at Outfall 023 are based on this regulation. The limitations for Oil and Grease at OutfalLs 0103, 004, 007, 009, Oll, 012, 013, 014, 015, 016, 017, 018, 019, 020, 021, 022, and 024, as done in the previous permit, are based on this regulation. 6. Applicable Federal Effluent Guidelines and Standards: The federal guidelinrs which apply to this type of facility are found under 40 CFR 434, titled Coal Mining Poim Sourcc Category BPT, BAT, BCT Limitations and New Source Ptrfatmance Standards. The limitations which apply are: Table VI - 4 - Fedetn! Standards Ptiiameter. .: 30 Dny Avg Concentratign . Daily Miax. Concenttntion Iron, total 3. S mg/1 7.0 mg/I 7SS 35 mg/l 70 mg/l Settleable Solids NA 0.5 ml/1 pH Between 6.0 s. u. and 9.0 s. u.