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HYDRO24004
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Entry Properties
Last modified
8/24/2016 8:44:15 PM
Creation date
11/20/2007 4:16:49 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981022
IBM Index Class Name
Hydrology
Doc Date
3/30/2004
Doc Name
Public Notice & Draft Permit (CO-0000132)
From
CDHO WQCD
To
DMG
Permit Index Doc Type
NPDES
Media Type
D
Archive
No
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I COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division <br />Rationale -Page S, Permit No. 00.0000132 <br />from a specific event and occurred through automatic dewatertng devices within 48 hours after measurable <br />precipitation has stopped. In addition, to waive sen/eable solids limitations, it is necessary to prove that an <br />event greater than the magnitude of the IO year, 24-hour event occurred. <br />For snowmelt to waive TSS and total iron limitations, it is necessary to prove that discharge directly resulted <br />from snowmelt and occurred through automatic dewatering devices within 48 hours after pond inflow has <br />stopped. 1n additon, to waive settleable solids limitations, it is necessary to prove that an event greater than <br />the magnitude of the applicable 10 year, 24-hour event occurred. <br />Documentation that the treatment facilities were properly operated and maintained prior 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 perminee could have controlled the discharge in such a <br />manner that primary limitations could have been met, whether proper sedimentstorage 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 ofdewatering. <br />Post-Mininr 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 fhe required contour and revegetation has <br />commenced, applicable discharges may be eligible for limitations other than those specified in Part I.A.I. In most <br />cases, these post-mining limitations shall remain in effect until bond release. The perminee shall notify the Division <br />at the appropriate time so that consideration ofpermit modifications can be made. Prior to notification and <br />subsequent permit modification, active mining limitations will apply regardless of actual mine status. <br />d. Pollutants Limited by Water Oualitv Standards /Outfa1101 S Onlvl: The water quality assessment in Appendix A <br />contains the evaluation ofpollutants limited by water quality standards applicable to outfa1101 S. The mass balance <br />equation shown to Section IV ojAppendix A was used for metals to calculate the maximum allowable effluent <br />concentration, M_, that could be discharged without causing the water quality standard to be violated. A detailed <br />discussion ojthe calculations for the maximum allowable effluent pollutant concentrations for metals is provided in <br />Section IV of the water quality assessment contained in Appendix A. <br />The maximum allowable effluentpollutantconcenttations determined as part ojthese calculations represent the <br />calculated effluent limits that would be protective of water quality. These are also known as the waterquality-based <br />effluent limits (WQBEIs). <br />The Permits Unit evaluated the calculated WQBELs and has made a determination as to whether there is a <br />reasonable potential for thefacility discharge to cause or contribute to an exceedance ofa stream standard. If there <br />is a reasonable potential for the discharge to contribute to an exceedance, effluent limiu are included in the permit. <br />For metals, a quantitative approach to reasonable potential evaluations is utilized as drscussed in following <br />paragraphs. <br />Metals: Utilizing the assimilative capacities contained in Appendix A, an analysis must be performed to <br />determine whether to include the calculated WQBELs in the permit. The guidelines for performing a <br />reasonable potential analysis are outlined in the Division's document, Determination ofthe Requirement to <br />Include Water Quality Standards-Based Limits in CDPS Permits Based on Reasonable Potenh'al Procedural <br />Guidance. dated December 2002. This guidance document utilizes both quantitative and qualitative <br />approaches to establishing reasonable potential depending on the amount of available data. Per the <br />Procedural Guidance, a quantitative determination of reasonable potential requires a minimum often data <br />points. <br />There was not sufficient effluent data to conduct a quantitative analysis for any metal since outfal7 015 has not <br />yet discharged. There were no effluent data for tots! recoverable (TR) arsenic, potentially dissolved (PD) <br />cadmium, TR trivalent chromium, PD copper, dissolved and TR iron, PD manganese, total mercury, PD nickel, <br />PD selenium, PD silver, and PD zinc, and therefore monitoring will be prescribed, as discussed subsequently, <br />prior to the determination of the need for effluent Iimiis. <br />Lnst Revisedr 3/19/2004 <br />
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