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Page 1! COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale -Page 19 Pennlt No. CO-0045675 VI. TERMS AND CONDITIONS OF PERMIT A. Determination of Elf/uent Limitations (Cont.) 4 Discussion of Etttuent Limitations (Cont.) c) Pollutants Limited by Water Ouality Standards -For the parameters shown in Table VI-3, the mass balance equation shown in VI-A.2. was used to calculate the allowable eRluent limitations that would not cause the water quality standards to be violated. These IimitaUons are shown as the values for M= in Table Vt-3. The values for Or, Qa and O, fa chronic and acute limitations, taken from section 111.8.2, o/ this rationale, end used in the calculations (or water quality limited parameters are: Flow ~ Chronic (30E3) ~; Acute (iE3) Q, 1.8 cfs 1.3 c(s OOIa = 0.89 cfs OOfa = 0.89 cfs ps OOfb = 0.557 cfs 001b = 0.557 cis 001 c = 0.245 cfs 001 c = 0.245 c/s 001 a = 2.69 cfs 001 a = 2.19 cfs Q, 0016 = 2.36 cfs 0016 = 1.86 cfs 001c =2.045 cfs OOIC =1.545 cfs Values for M, and M, vary depending on the background stream quality data (M,) and the applicable water qualtty standard (M~. The hardness-based TVS metal standards were determined with a mean total hardness value of 64 mg/1 as CaCO,. The M, and M, values are shown in Table VI-3 along with the calculated eHfuent limitations (M~. In addition, Table VI-3 contains the anb'degredadon-based water quality standard and limitation where this is applicable. Table VI-3 shows the calculations for a facility Bow limitation (or outfall 0016 of 250 gpm (or 0.36 MGD, or 0.557 cfs). For the calculations for the other tiered Bow limits o(400 gpm (001a) and 110 gpm (001c), as well as for the determination of baseline loads for this permit, refer to Appendix B. d) Antid radation Review: Because segment 28 does not include a Use Protected classi0cation, an anbdegredation reviewls required for this permit since this is a new discharge. As is discussed in Section 31.8 ofthe Basic Standards and Alethodoloaies for SuAace Wafer (SCCR 1002-31), antidegredation reviews are required to be peAormed for new dischargers to a reviewable stream segment that is not use protected. As indicated in 31.8(3)(c) of the Basic Standards. the initial step in an antidegredation review is a determination whether the activity in ques8on is likely to result in significant degradation of reviewable waters, with respect to adopted narrative or numeric standards. The sign~cance determination is based on the chronic numeric standard and Bow for the pollutant of concern except for those pollutants which have only acute numeric standards in which case the acute standard and flow will be used. The activity shall be considered not to result in sign cant degradation, as measured in the reviewable waters segment, rf (i) The Bow rate or volume of a new or increased discharge under review is small enough that it will tie diluted by 100 to 1 or more at low Oow, as defined in section 31.9, by water in the stream; or (ii) The new or increased loading from the source under review is less than 10 peroent of the exisa'ng total load to that segment (or cri0cal constituents (e.g. those (or which there are stream standards set and which are present in the discharge); provided, that the cumulative impact of increased loadings Irom all sources shell not exceed f0 percent of the baseline total load established (or the segment (the baseline total load shall be determined at the time of the Orst proposed new or increased water quality impacts to the reviewable waters.); or (iU) The new or increased loading Irom the source under review will consume, after mixing, less than 15