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COLORADO DEPARTMENT OF PUBLIC HF-AL.TH AND ENVIRONMEM; Water Quality Control Division <br />Ratiunale•- Page ]2, Permit No. CO-0000221 <br />3) Acute WEl Limitations - Outfalls 002. 003. 005. 006, 010 and OII: The Division has found [ha[ discl~ <br />of pit pumpage, spoils spring water and similar sources from coal mines at similar sites have erhibitm <br />efJlueN toxicity and toxicity failures have previously occurred for some of the discharges at this facility. n <br />this basis, the Uivisiort believes there is reasonable potential for the discharges from outfalls c102, 003, 005, <br />006, 010 and 0.11 to interfere with attainment of applicable water quality clussificatiotu or stcvtdards. <br />Because of this, the acute toxicity limit has been incorporated into the permit and becomes effective <br />immediately. The permi[[ee is required ro conduct routine moni[oring, the resu![s of which one ro be <br />reported as an i;C~. /f the LC,c 5 100% efflueru, the permitree is required to conduct the m~tomatic <br />compliance schedule as identified in Pan I.A.4.c. of the permit. <br />4) Chronic WET Limitations - Outfalls 004 and 008: Outfalls 004 and 008 discharge to Fish Cretk, which is <br />within segmem .l36. This segmem is classified aquatic life, class 1, with all of the appropriate aquatic life <br />numeric standards. Thus, the default to acute testing applied to the other ourfalls does nor apply to outfalls <br />004 and 008. Further, because of the variable nature of coal mine drainage aM spoil spring (lows and <br />their correlation to stream flows, it is appropriate to look beyond annual flows to determine more realistic <br />seasowl /WC's for these tx~o outfalls. 77re Division used discharge flow values for each outfall that <br />represent the mean of the ntonshly average flows for each rwnth over the period from 1986 through 1996 in <br />conjunction with the 30E3 developed by the Division for Fish Creek. From these results, the Idghest <br />moruhly IWC per calendar quarter was selected as the quarterly IWC. The monthly flows and <br />corresponding IWC for outfalls 004 and 008 are shown in the following table. The selected Iti'/Cs are <br />highlighted in Bold and Double-Underlined. <br />Table VI-8 -Mean Monthly Discharge Flows for Period 1986 - 1996 (cfs) and Corresponding IR'Cs <br />Out- Jan Feb . .Mar Apr May . Jun Jul Aug Sep - Oct .Nor Dec <br />fem. <br />004 .0546 .0889 .2660 .5048 .2909 .118/ .0807 .0629 .0609 .0650 .0673 .0 <br />Flow <br />~C 3.3 5.3 10.8 12.3 6.1 9.0 16.8 17.3 ]6.9 7.5 7.8 3.3 <br />008 .0314 .0395 .28]3 .3673 .2068 .0933 .0706 .0493 .0427 .0580 .042.9 .0422 <br />Flow <br />008 1.9 2.4 11.3 9.3 4.4 7.2 15.0 14.1 12.5 6~8 5.0 2.7 <br />IR'C <br />On the same bans as stated for acute [imitations above, the Division believes there is reasonable potential <br />for the discharges from outfalls 004 and 008 ro interfere with attainment of applicable water quality <br />classifications or standards. Because of this condition, the chronic limit is continued in the permit and <br />becomes effective immediately. The permittee is required to conduce routine monitoring. 7&e results of the <br />[esting are to be reported on Division approved forms. The permittee will be required [a conduct a <br />statistical derivation on the data, looAing for any statistically significant difference in toxicity between the <br />control and the effluent concentrations. This set of calculations will look ar the full range of to.ciciry <br />(lethality, growth and reproduction). Ija level ojchronic toxicity occurs, such that there is a s[aris[ically <br />significant difference in the lethaliry~ (at the 95%r confidence level) benveen the contra! and any effluem <br />concentration less than or equal to the Instream Waste Concentration (IWC), the permittee will be required <br />ro follox• the automatic compliance schedule identified in Pan I.A.S. c. of the permit, if the observed toxicity <br />is due to organism lethality. Only ezceedance ojthe limitation specified in Pan l.A.l.f. will trigger the <br />requirement for conductirsg the automatic compliance schedule identified in Part I.A. S. c. of the permit. Ij <br />the toxicity is due to differences in the growth of the fathead minnows or the reproduction of the <br />Ceriodaphnia, no immediate action on the part of the permittee will be required. However, this incide <br />along with other WET data, will be evaluated by the Division and may form the basis for reopening the _ <br />permit and including additional WET limits or other requirements. <br />