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COLORADO DEPARTMEM OF PUBLIC HE Rationale -Page 12, Permit No. CO-0000221 3) ojpit prrmpage, spoils sprin, effluent toxicity and tosiciry this basis, the Division belie 006, 010 and 011 to imerfet Because ojthis, the acute tc immedituely. The permirtee reported as an LC,~. IJ the compliance schedule as ides 4) within segmem 13b. This numeric standards. Thus, 004 and 008. Funkier, bet their correlatiors to stream seasonal IWC's jot these n represent the mean of the t conjunction with the 30E3 monthly /WC per calendar corresponding /WC jot ou( highlighted in Bold and D~ AND ENVlRONMElrl; Water Quality Control Division alts 002. 003. 005. 006. 010 and OI1: The Division has found that discharges water and similar sources from coal mines at similar sites have exhibiru inures have previously occurred for some ojthe discharges at this jadlit es there is reasonable potemial for the discharges from outfalls 002, 00~, 005, with atrainmeru of applicable water quality classifications or standards. iciry limit has been incorporated imo the permit and becomes eJj'ective s required to conduct routine monitoring, the results ojwhich are to be Cw <_ 100% effluent, the perminee is required to conduct the automatic (ted in Pan /.A.4.c. of the permit. utfalls 004 and 008: Outfalls 004 and 008 discharge ro Fish Creek, which is meet is classified atptatic life, class 1, with all of the appropriate aquatic life default to acute test!ng applied to the other outfalls does not apply to outfalls se of the variable na,•ure aJ coal mine drainage and spoil spring flows auf ws, it is appropriate to look beyond annual flows to determine more rea:istic outfalls. The Division used discharge flaw values for each ourfa[l that vthly average flows for each momh aver the period from 1986 through 1 X96 in ueloped by the Division for Fish Creek. From these results, the highest aver was selected as the quarnrly 1 WC. The monthly flows and Ls 004 and 008 are shown in the following table. The selected IWCs are Table VI-8 -Mean Monthly Discharg~ Flows jot Period 7986 - 1996 (cjs) and Corresponding IWCs Out- jau Jan Feb Mar A I pr May Jun Jul Aug Sep Oct- Nov - . ltec 004 .0546 .0889 .2660 .5 8 .2909 .1787 .0807 .0629 .0609 .0650 .0673 _ .G Flow ~ 004 3.3 5.3 10.8 l .3 6.1 9.0 16.8 77.3 16.9 7.5 7.8 :'.3 IWC ° 008 .0314 .0395 .2813 .3 73 .2068 .0933 .0706 .0493 .0427 .0580 .0424 .L422 Flow 008 1.9 2.4 ]1.3 9 3 4.4 7.2 75.0 14.1 12.5 6.8 5.0 :'.7 On the same basis as stated Jor the discharges from outfi classifications or standards. becomes effective immeditue resting are ro be reported oc statistical derivation on the control and the effluent cont (lefhaliry, growth and reprot significant difference in the concentration less than ar et to follow the automatic com! is due to organism lethality. requiremem for conducting i the toxicity is due to differet Ceriodaphnia, no immediate along with other WET data, permit and including tulditic for acute limitations above, the Division believes there is reasonable potential 1!s 004 and 008 to interfere with attainment of applicable water qualify Because ojthis condition, the chronic limit is continued in the permit and ~•. The permiffee is required to conduct ravine monitoring. The results oJthe Division approved forms. The permittee will be required to conduct a Tara, looking jot am statistically significant difference in toxicity between the entrations. This set of calculatioru will look at the full range of toxicity 'action). Ifa level of chronic toxicity occurs, such that there is a statisti~:alh~ ethaliry (af the 95~o confidence level) between the control and any efflue,tt Dual to the Insrream A'aste Concentration (IlVC), the permittee will be required ~liance schedule identified in Part l.A.S.c. ojthe permit, if the observed toxicity Only exceedance of the limitation specified in Pan I.A.l.j. will trigger the he automatic compliance schedule idemified in Pan I.A.S. c. of the permi!. IJ ces in the growth of the fathead minnows or the reproduction of the action on the pan of the permitree will be required. However, this incident will be evaluated by the Division and may form the basis for reopening tl it~ wl WET limits or oth,sr requiremems.