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:OLORADO DEPARTMEM OF PUBLIC HEALTH AND ENVIRONMENT, Water Quafiry Control Division ;rationale-Page 5, Permit No. CO-0038776 ' For rainfall, to waive TSS and total iron limitations, ii is necessary to prove that discharge occurred within 48 hours after measurable precipitation has stopped. In addition, to waive settleable solids limitations, it Is necessary to prove that discharge occurred within 48 hours after precipitation greater than the 10 year, 24-hour event has stopped. For snowmelt to waive TSS and total iron limitations, it is necessary to prove that discharge occurred within 48 hours after pond inflow has stopped. In addition, to waive settleable solids limitations, it is necessary to prove shat discharge occurred within 48 hours after pond inflow volume greater than the 10-year, 24-hour event has stopped. Documentation that the treatment facilities were properly operated and maintained prior to and durin the storm event must be submitted with any request for relief. The Division shall determine the adequacy of proofg As part of this determination, the Division shalt evaluate whether the permitiee could have controlled the duchar&e to such a manner that primary limitations could have been met, whether proper sediment storage levels were maintained and the ponds had sufficient water and sediment capacity for the storm event plus other relevant factors. All manual pond dewatering must meet TSS and total iron limitahons unless previous approval has been granted for ponds that have no other method of dewatering. Post~Minin~Are~as: In conformance with 40 CFR 434.50, commencing at the time active mining has ceased and all surface areas served by a sedimentation pond have been returned to the required contour and reveggetation has commenced, applicable discharges may be eligeble for limitations other than those specs~t'ed in Part LA.J. In most cases, these posf- mtning limitations shall remain in e/~ect until bond release. The permittee shall noti(y the Division at the app roprsate time so that consideration ofpermit modifications can be made. Prior to notification andsubsequent permit modifcahon, active mining limitations wil apply regardless of actual mine slates. e. Pollutants Limited by Water Oualit~tandards: The water quality assessment in Apppendix A contains the evaluation of po utants invite y water qua sty standards. The mass balance equation shown in Section !V of Appendix A was used for pollutants. to calculate the maximum allowable e~~jj]]went concentration, M1 that could be discharged without cousin the water quality standard to be violated. A detailed discussion of the calculations for the maximum allowable a went pollutant concentratiors for fecal coliform, total residual chlorine, ammonia and metals is provided in Section IV~f the wafer quality assessment contained in Appendix A. The maximum allowable e(~luent pollutant concenh~ations determined as part of these calculations represent the calculated ej}luent limiu that would be protective of water quality. These are also known as the water quality-based effluent limiu ( BELs). The Permits Unit evaluated the calculated WQBELs and has made a determination as to whether there is a reasonable potential for the facility discharge to cause or contribute io an exceedance of a stream standard. 7j there is a reasonable potential for the discharge to contribute to an exceedance, effluent limits are Included in the permit. i. Fecal colt orm total residual chlorine and ammonia: Far fecal coliform and fotal residual chlorine, the previously iscusse imtu are more stringent t an ca cu ate WQB Ls and therefore are applicable. Thus, a reasonable potential analysis was not performed and no further discussion of these pollutants is provided. For ammonia, ancillary and/or additional treatment technologies are often employed to reduce the ammonia concentrations. A facility may currently discharge ammonia at low-level concentrations to meet e~~/fl1uent limitations and therefore their effluent discharge shows no reasonablepotential to cause or contribute to exceedances of instream standards. However, absent !initiations, a facility may no ion er continue such pollutant reductions and therefore the discharge will have reasonable potential. For this reason, s~e Permits Unit performs a qualitative determination of reasonable potential for ammonia, For total ammonia, the assimilative capacities shown in Appendix A are much greater than levels achieved by current treatment technology. Thus, total ammonia limitations are not imposed and no monitoring is required. ii. Metals.-- Ou ails 004 011 012 013 016 and 017: UtiliG-inQ the assimilative capacifies contained in Appendix A, aria sis must a pe orme to etermine w et er to include the calculated WQBELs in the permit. The gguuidelines ..,,.r~ ,.,:.,T „ ,..,,.,,.,mt~,o runannnhto narenrial /RPI analvsis are outlined in the Division's document, Deierminat on the amouhr The first step, determining the pollutants of concern, the permit writer, with the coo erasion of the permittee, must use best professional judgment to determine the pollutants o~ concern ("POC's'). PPOC's are pollutants that might be expected in the effluent. POC's may be: pollutants that have been detected in the effluent (through coinpdance monitoring, priority pollutant monttoring, optional monitoring, or other monitoring) in the last 5 ears; pollutants with known sources; pollutants that are known to commonly occur to similar effluents pollutants that are present in the influent or at other samplin points in the treatment or collection systems; ~oflutants that are present in the bioso tdr or other treatment resi~uals; other pollutants which, in the permit writer s best professionalludgment, may be found in the effluent. The permittee provided upstream and downstream data from the West Elk Mine, which represents instream quality before and after the ducharge(sl. This data was compared with additional ambient data provided in the water quality assessment (Appendix A Table A-ti), and compared wtth the WQBELs to determine what the POC's were. Additionally, with the rjevelopmeat of ELGs for the Western Alkaline Coal Mining Subcategory, there was a consideration of what potential pollutants were pollutants of concern. Whereby, it was determined that total iron was the only pollutant of concern. The limitations for total recoverable iron are lower than some a uent monitoring results summarized in Table V-3. For this reason, a compliance schedule is included in the permit ~ee Part LA.B. f to give the permittee an opportunity to assess their treatment system's capability of meeting these limitahons, and design and construct additional treatment facilities, if they are deemed necessary. The permittee will be required So submit a Preliminary Report by December 31 2004, detailin their plan for bringing the discharge into compliance with the find[ limitations that become e~ecrive January ~ 2007 Because the previous permit had no limitations for these metals, none will be applied during the interim period. The reallocated limitations will be used as the final limitation. This compliance schedule applies to Outfa11017A. Lass Revised: 4/19/1004