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COLORADO DEPARTMENT OF PUBLICHEALTHAND ENVIRONMENT, Water Quality Control Division
<br />Rationale -Page 6, Permit No. CO-0032115
<br />30 Day Avg Daily Max
<br />pH, s:u. (minimum -maximum) --6.0 - 9.0--
<br />Total Suspended Solids, mg/1 * 35 70
<br />Total Iron, mg/1 *
<br />BAT** 3.5 7.0
<br />NSPS*** 3.0 6.0
<br />Settleable Solids.ml/1* N/A 0.5
<br />` These parameters subject to Burden ojProofReguirements, see neat section
<br />" Besr Available Technology -applies ro those ponds constructed prior to 5/4/1984
<br />*** New Source Performance Standards -applies to those ponds constructed after 5/4/1984
<br />Alternate Limitation Burden of ProofReauirements: In conformance with 40 CFR 434.63, the permittee has the
<br />burden ofproof when requesting relieffrom total suspended solids (TSS), total iron and/or settleable solids
<br />limitations. Relief shall be granted only when necessary and shall not be granted when the permiaee has control
<br />over the discharge. The permittee should endeavor to meet the primary limitations whenever possible. The Division
<br />shall have final authority in determining whether relief is granted. Discharges from all outfalls are eligible for this
<br />exemption, however, the majority of the loading from any discharge has to consist ofsrorm runofffor the relief to be
<br />available for any discharge. Outfalls 001, 002, 005, 008, 009, 012, 013, 014, 01 S, 016, 018, 021, and 024 consist
<br />entirely of surface runoff, thus all discharges from these thirteen ovifalls should be eligible, providing the proper
<br />demonstration is submitted and approved.
<br />i. For active out(alls: For rainfall, to waive TSS and total iron limitations, it is necessary to prove that discharge
<br />occurred within 48 hours after measurable precipitation has stopped. In addition, to waive settleable solids
<br />limitations, it is necessary to prove that discharge occurred within 48 hours after precipitation greater than the
<br />]0 year, 24-hour evens has stopped. For snowmelt, to waive TSS and total iron limitations, it is necessary to
<br />prove that discharge occurred within 48 hours after pond inflow has stopped. In addition, to waive settleable
<br />solids limitations,. it is necessary to prove that discharge occurred within 48 hours after pond inflow volume
<br />greater than the 70 year, 24-hour event has stopped.
<br />ii. For oost-minim outfalls: For rainfall, to waive settleable solids (imitations, it is necessary to prove that
<br />discharge occurred within 48 hours after precipitation greater than the 10-year, 24-hour event has stopped.
<br />For snowmelt, to waive settleable solids limitations, it is necessary to prove that discharge occurred within 48 .
<br />hours after pond inflow volume greater than the ]0 year, 24-hour event has stopped.
<br />Documentation that the treatment facilities wereproperly operated and maintainedprior to and during the storm
<br />event must be submitted with any request for relief. The Division shall determine the adequacy of proof. As part of
<br />this determination, the Division shall evaluate whether the permittee could have controlled the discharge in such a
<br />manner thatprima~y limitations could have been met, whetherproper sediment storage levels were maintained and
<br />the ponds had sufficient water and sediment capacity for the storm event plus other relevant factors. All manual
<br />pond dewatering must meet TSS and total iron limitations unless previous approval has been granted for ponds that
<br />have no other method of dewatering.
<br />Post-Mining Areas: In conformance with 40 CFR 434.50, commencing at the time active mining has ceased and all
<br />surface areas served by a sedimentation pond have been returned to the required contour and revegetation has
<br />commenced, applicable discharges may be eligible for limitations other than those specified in Part I.A. 1. In most
<br />cases, thesepost-mining limitations shall remain in effect until bond release. Thepermittee shall note the Division
<br />at the appropriate time so that consideration of permit modifications can be made. Prior to no4fication and
<br />subsequent permit modification, active mining limitations will apply regardless of actual mine status.
<br />d. Pollutants Limited by Water OualiN Standards: The water quality assessment in Appendix A contains the
<br />evaluation ojpoilutants limited by water quality standards. The mass balance equation shown in Section IV of
<br />Appendix A was used for all pollutants to calculate the maximum allowable effluent concentration, MZ, that could be
<br />discharged without causirsg the water quality standard so be violated. A detailed discussion of the calculations jot
<br />the maximum allowable effluent pollutant concentrations for metals are provided in Section IV of the water quality
<br />assessment contained in Appendix A.
<br />The maximum allowable effluent pollutant concentrations determined as parr of these calculations represent the
<br />Last Revised: anvnooa
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