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COLORADO DEPARTMENT OF PUBLIC HEALTHAND ENVIRONMENT, Water Quality Control Division Rationale, Page 8, COG-0850000 Coal Mining General Permit Alternate Limitations For Acid Or Ferruginous Mine Drainage From Coal Refuse Piles And From Steep Slone Areas Or _ Mountaintop Removal Operations - Table III-5e contains limitations for any discharge or increase in the volume of a discharge caused by precipitation within any 24 hour period greater than the .1-year, 24-hour precipitation event, but less than or equal to the 10 year, 24-hour precipitation event (or snowmelt of equivalent volume) may may substitute the following limitations for these specific parameters only, subject to burden of proof requirements described in Part I.B.4 Table III-5e: Alternate Effluent Limitations and Monitoring Requirements -Acid or Ferruginous Mine Drainage Pririmteter Limitations 30-Day 7-Day Daily Rationale Monitoring Freqirencv Sample Tipp' Aig, Max. Federal Effluent Limitation Guidelines Total Suspended Solids, mg/1 Report NA Report Federal ELG Weekly Grab Total Manganese, mg/1 Report NA Report Federal ELG Weekly Grab Total Iron, mg11 Existing Sources (before514184) Report NA Report Federal ELG Weekly Grab New Sources (after 514184) Report NA Report Settleable Solids mbl Report NA 0.5 Federal ELG Weekly Grab IV OTHER PERMIT CONDITIONS a. Regulations for Effluent Limitations (Regulation No. 62) - Section 62.4 of the regulations includes effluent limitations that apply to all discharges of wastewater to State waters. These regulations are the basis for the oil and grease limitations in the tables above. Note that the limitations for TSS are not included in many cases due to the presence offederal ELGs. b. Technology-Based Limitations (Federal Effluent Limitation Guidelines) -Federal Effluent Limitation Guidelines (ELG's) guidelines have been promulgated for these facilities and must be applied to these discharges, unless a more stringent Water Quality Standard exists. The Water Quality Standards in many areas of the state are often more stringent than the federal -` ELGs, and therefore may be substituted in a certification. c. Water Quality Standard-based Limitations (DischaMes to Surface Waters)- Water quality-based limits are imposed for pH. Water quality-based reporting may also be imposed for other pollutants of concern based on the discussion that follows. 1. RHH- This parameter is limited by Water Quality Standards as the water quality standards of 6.5-9.0 s.u. range are more stringent than those specified under the Regulations for Effluent Limitations. 2. Metals - The permit writer will review the application and determine if any metals parameters must be limited and/or monitored to protect the classified uses assigned to the receiving water. If required, the permit writer will set these limitations equal to the appropriate water-quality standards. As many water quality standards for metals are listed as TVS, and based upon an equation dependent on the hardness of the receiving stream, the permit writer will obtain hardness data to determine the appropriate metals limitations where appropriate. If a water quality based limitation for metals is considered in the permit, the more stringent of the federal ELG and the water quality based limit will be applied. 3. Organics - The permit writer will review the application and determine if any organic parameters must be limited and/or monitored to protect the classified uses assigned to the receiving water. If required, the permit writer will set these limitations equal to the appropriate water-quality standards. 4. Chemicals- The addition of chemicals (including release agents) to the discharge is not allowed unless expressly authorized by the Division. If authorized, all chemicals must be used and stored in accordance with the manufacturers' recommendations and in accordance with any applicable state or federal regulation. d. Salinity Requirements - All permit actions for discharges to surface waters in the Colorado River Basin must include salinity monitoring. Accordingly, the permit writer will perform an analysis, as set out in the paragraphs that follow, to determine _ which salinity requirements apply pursuant to the requirements of Section 61.8(2)(1) of the Colorado Discharge Permit S sy tem Regulations(Re- elation No. 61). Multiple discharges covered fi-om a single facility are subject to the limitation that would apply if there were a single discharge point. Based on the effluent data in the application from a new facility, the permit writer will make an assessment of the expected salinity load in the discharge (from concurrent flows at all ouf ills) and if less than I ton/day or 366 tons/year, the calculation will ho dnrlnxvntod in tho i"ued certification. For facilities discharging less than this threshold. auarterly monitoring will be