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may be granted for each discharge occurrence only when necessary and shall not be granted when <br />the permittee has control over the discharge. The permittee should endeavor to meet the primary <br />limitations whenever possible. <br />a) 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 <br />settleable solids limitations, it is necessary to prove that discharge occurred within 48 hours after <br />precipitation greater than the 10 year, 24-hour event has stopped. <br />Relief from primary TSS and Total Recoverable Iron limitations at Outfall 004A: Please see <br />004A Exceedence Report attached to this submittal for more detail and back-up information. <br />Rainfall was recorded at Colowyo on October 16 and 17, 2006, the day prior to and the day <br />sampling was completed at this location. Inflow into this pond is primazily in the form of <br />stormwater runoff at this time. Colowyo believes this specific incident of exceeding primary TSS <br />and Total Recoverable Iron limitations is due primarily to increased stormwater runoff caused by a <br />storm event the day prior to and the day of sampling. <br />Colowyo performs PE reviewed pond inspections of all NPDES ponds on a quarterly basis as <br />mandated by CDMG/Colowyo Permit requirements. These quarterly inspections aze reviewed by <br />CDMG staff and specific guidance, maintenance issues, and improvements are discussed as <br />necessary with Coloywo's assigned CDMG inspector (currently James Stark). <br />Outfall 004A was cleaned out in December 2004, and all sediment accumulation was removed at <br />that time. The available sediment volume storage capacity for the pond during the third quarter <br />was well below any tilt level for permit compliance. Ponds are targeted for cleanout in the event <br />one of two criteria aze met; either the pond approaches 60% available storage capacity, or the rate <br />of sedimentation suggests the pond will receive enough sediment to reach 60% available capacity <br />during the course of the following year. As a matter of convenience, sediment was removed from <br />this pond during November 2006 even though no thresholds requiring cleanout were reached. <br />In an effort to further minimize issues with TSS limitations, Colowyo is in communication with GE <br />Betz in order to identify any acceptable products on the mazket that could be more effective at <br />settling out suspended materials. Testing is in progress to evaluate the relative effectiveness of <br />these products. <br />Colowyo is currently evaluating opportunities for improving the manner in which stormwater <br />enters the pond. Modifications to in-pit drainage structures and conveyance ditches may be <br />warranted if opportunities for minimizing particle/sediment loading are discovered. This is an on- <br />going process and improvements will be implemented as they are identified. <br />Because Colowyo's ponds are flow-through treatment ponds and not containment ponds, it is not <br />possible to impound waters for an extended period of time once discharge levels have been <br />reached. These ponds were designed to treat stormwater inflow for settleable solids to a level of <br />0.0 mUl during a 10-yeaz 24-hour storm event. <br />It is Colowyo's belief that due diligence, good faith efforts and in-house procedures and practices <br />were followed prior to, during, and after the exceedence of TSS and Total Recoverable Iron <br />Colowyo Mine • 5731 Stale Highway 13 • Meeker, Colorado 81641 <br />T +1 970 824 1500 • P +1 970 824 1504 • www.rtea.c°m <br />