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COLORrfI)O DF.I'ARTM/iA'T OF fIEALTH, Water Quality Gnurul Diviaiun Kminrvde - Pr{(r l7, permit Na. CO-00.72(5.4R 40 CFR Part 434 Subpart B contains effluent (imitations fur total iron, 7SS, and pH from coal prcparariun plant assoc. Subpart F, which contains alternate elJluent limitations jar precipitation evenec, states that any discharge or increase in the volume of a discharge from coal preparation plant areas enured by precipitation within any 24-hour period less than or equal to the /0-year, 24-hour precipitation event (ar snowmelt of equivalent volume) may comply with the setleable solids and pH limitations. Any discharge or' increase in the volume of a discharge caused by precipitation within any 24-hour period greater than the 10-year, 24-hour precipitation event (or snowmek of equivalent volume) may comply with the pH limitation only. Since Outfall 001 contains discharges from coal preparation plan[ areas, the ej/luent limitations contained in Subpart B and Subpart F apply to this discharge. In adduion, Outfalis 004 and 005 contain surface runoff from the site. Since the efjTuem quality from Outfall 004 and Outfall 005, in the everu it is activated, is expected to be similar in the quality of effluem discharged from Ourfall 001, as done in the previous permit, the limitations for OutfaU 001 will apply to Otttfa/is 004 and 005. When the previous pcrn+ir was issued in May 1987 and amended in October 1987, Outfal! 002 consisted of surface runoff from active mining areas and spoilt spring water. Since this discharge no longer comains runoff from active areas and spoils spring runoff and only consists of surface runoff from reclaimed areas ojthe site, the effluent guidelines applicable to this discharge are Subparts E and F. Similarly, Outfall 003 used to contain surface runoff from reclamation areas and spoils spring xater. Now, Outfall 003 only comains surface runoff from reclaimed areas. Since this discharge no longer contains.runofffrom reclamation areas and only oonsisu of runafffrom reclaimed areas of the site, the effluem lirnitatians aj Subparts E and F arc applicable a this discharge. 40 CFR Parr 434 Subpart E contains ejjlucm dmitations for settleable solids and pH from reclamation areas. /n adduion, Subpar F rHhich comarns ahernate effluent limitations for precipitation evenu, states that any discharge or increase in the volume oja discharge from reclamation areas caused by precipitation within any 24 hour period greater than the 10-year, 24-hour precipitation everu (or swwmelt ojequivaJent uolumeJ may comply with the pH limitation instead. OutfaU 006 contains spoils spring water and does not receive treatment prior [o disrarge Since this discharge is continuous in nature, no alternate efJiuem limitations for precipitation events are applicable for this otttfall As addressed in the following section of shit rationale, the need for water quality-based efjluem limitations wiB be addressed at Outfal1006. As shown in Section 1!/.A.3, the rater quality limitations for pH arc trore stringent than the federal guidelines. Therefore, water quality~ws'ed limits, as done in the previous permit, will be incorporated into the proposed perntit at al! permitted outfalLs. c. Pollaanu limited by Water Quality Standards -Since OtttfalLs 001, 002, 003, and 005 only comain surface runoff, as done in the previous permit for outfalLs consisting of surface runoff only, no pollutants -were li»dted by water quality standards, with the exception of pH. Outfa/l 004 contains surface runoff from both active and inactive areal of the sue. As discussed in the previous permit rationale, the Colorado Mined Land Reclamation Division and the State Engineers Office require ponds to be dewatered within 36 to T2 hours after a precipitation event. On this basis, the Division believes that discharges wiU occur when the stream flow is well above the 7Q10 low flow of Trout Creek Thus, no water quality~liased effluent limitations other than pH were considered at OutfaU 004.