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HYDRO22023
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Entry Properties
Last modified
8/24/2016 8:43:10 PM
Creation date
11/20/2007 2:39:45 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980004
IBM Index Class Name
Hydrology
Doc Date
6/25/2004
Doc Name
NPDES Permit
Permit Index Doc Type
NPDES
Media Type
D
Archive
No
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9 COLORADO DEPARTMENT OF PUBLIC HEALTHAND ENVIRONMENT, Water Quality Control Divisabn <br />Rationale -Page 4, Permit Na. CO-0038342 <br />Alternate Limitation Burden of ProofReguirements /ADDlicable to putfaJ1001 Only: In conformance with 40 CFR <br />434.63, the permiuee has the burden of proof when requesting relieffrom total suspended solids (TSS), total iron <br />and/or settleable solids [imitations, as appropriate. The intent of this regulation is to afford relief only when needed <br />due to a volume ojwater generated by a specific storm event, it is not intended to be automatically applied to all <br />discharges caused by precipitation, nor to be used to discharge volumes in excess of that generated by the storm <br />event. On this basis, relief shall be granted only when necessary and shall not be granted when the permiuee has <br />control over the discharge, enabling them to meet the primary limitations. The permiuee should endeavor to meet <br />the primary limitations whenever possible. Because manual dewatering can be accomplished as time and <br />condirions permit, all manual dewatering shall be required to meet the primary limitations. The Division shall <br />determine the adequacy ofproof. As part of this determination, the Division shall evaluate whether the permiuee <br />could have controlled the discharge in such a manner that primary limitations could have been met. <br />For rainfall. to waive TSS and total iron limitations, it is necessary to prove that discharge directly resulted <br />from a specific event and occurred through automatic dewatering devices within 48 hours after measurable <br />precipitation has stopped. In addition, to waive settleable solids limitations, it is necessary to prove that an <br />event greater than the magnitude of the 10-year, 24-hour event occurred. <br />For snawmelt 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. In addition, ro waive settleable solids [imitations, 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 fo 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 permiuee could have controlled the discharge in such a <br />manner that primary limitations could have been met, whether proper 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 ofdewatering. <br />Post-Minin¢ 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 revegetauon has <br />commenced, applicable discharges may be eligible for Itmitalons other than those specified in Part I A.1. In most <br />cases, these post-mining limitations shall remain in effect until bond release. The permiuee 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 ojacmal mine status. <br />d. Pollutants Limited by Water Oua1tN Standards (Out(al! 002 Onlv): The water quality assessment in Appendix A <br />contains the evaluation of pollutants limited by water quality standards applicable to outfa11002. The mass balance <br />equation shown in Section IV ofAppendix A was used for metals to calculate the maximum allowable effluent <br />concentration, My that could be discharged without causirsg the water quality standard to be violated. A detailed <br />discussion of the calculations for the maximum allowable effluent pollutant concentrations for metals is provided in <br />Section !V ofthe water quality assessment contained in Appendix A. <br />The maximum allowable effluent pollutant concentrations determined as part of these calculations represent the <br />calculated effluent limits that would be protective of water quality, These are also known as the water quality-based <br />effluent limits (WQBELs). <br />The Permits Unit evaluated the calculated WQBELs and has made a determination as to whether there is a <br />reasonable potential for the facility discharge to cause or contribute to an exceedance of a stream standard. If there <br />is a reasonable potential for the discharge to conuibute to an exceedance, effluent limits are included in the permit. <br />For metals, a quantitative approach to reasonablepotenual evaluations is utilized as discussed in following <br />paragraphs. <br />i. Metals: Utilizing the assimilative capacities contained in Appendix A, an analysis must be performed to <br />determine whether [o 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 />Last Revt:ed 6/9/2004 <br />
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