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COLORADO DEPARTMENT OP HEALTH, Water Quality Control Division <br />Rationale - Page 6. PERMIT NUMBER: COG-850000 <br />• <br />EFFLUENT LIMITATIONS: (Continued) <br />Table 4 <br />(Final Limitations) <br />• <br />Parameter Limitation <br />Flow (MGD) <br />pH (s.u.) <br />011 and Grease (mg/1) <br />Settleable Solids (ml/1) <br />Total Dissolved Solids (mg/1) <br />.(Colo. River Basin) <br />Total Phosphorus, as P (mg/1) <br />(Mllon Reservoir basin only) <br />Active Mining <br />Hasis <br />Report Monitoring Only <br />6.5-9.0 WQS <br />10 SES <br />0.5 SAT/NSPS <br />Report Monitoring Only <br />Report Monitoring Only <br />Limitations for pH and oil and grease apply to all discharges, regardless of <br />preclpitati.on conditions. Additionally, TSS and total iron 1lmitations apply <br />unless ezempted as described herein. The permittee may submit documentation <br />proving that discharge was precipitation induced. Upon acceptance by the <br />division of said proof, the settleable solids limitation will apply in place <br />of the TSS and total iron limitations. Similarly, upon acceptance of proof <br />that discharge was caused by precipitation greater than the 10-year, 24-hour <br />event (or equivalent snowmelt volume) compliance with TSS, total iron and <br />settleable solids limitations will be exempted. This means such a discharge <br />would be subject to pR and oil and grease limitations only. The division <br />allows these ezemptiona for a period up to 48 hours after measurable rainfall <br />has stopped or, for snowmelt, within 48 hours after Saflow to the <br />sedimentation pond has ceased. After such time, TSS and total iron <br />limitations shall be met. <br />Ezample 1: The area served by sedimentation pond and outfall 002 <br />receives 1.4 inches of rainfall during one 24-hour period (the 10-year, <br />24-hour event for this site is 1.7 inches). The permittee colleFta <br />samples at the outfall 18 hours after rainfall has ceased. The permittee <br />submits rain gauge data with the sample results to the division and <br />requests that the settleable solids limitation be substituted for TSS and <br />total iron limitations. Upon acceptance of the proof, the division will <br />determine compliance with settleable solids limitation and disregard TSS <br />and total iron reaulta. The division requires monitoring for all <br />parameters regardless of whether an ezemption is sought. <br /> <br />