2019-12-13_REVISION - M1980244 (55)

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STORMWATER MANAGEMENT PLAN NEWMONT CRIPPLE CREEK AND VICTOR GOLD MINING COMPANY embankments will be constructed to withstand the peak flow associated with at least two times the 10-year, 24-hour storm event. An overflow spillway or equivalent water release structure will be provided to protect the structural integrity of the embankment as well as avoid excessive erosion of the downstream streambed. The spillway or water release structure will be designed to pass the peak flows from a 100-year, 24-hour storm event. Stormwater ponds capable of handling at least two-times the 10-year, 24-hour precipitation event will be maintained until reclamation activities within the contributing watershed is completed. Diversion of surface runoff from undisturbed and reclaimed areas around the EMPs will be employed where appropriate. Discharges of stormwater are not expected to occur under the 10-year, 24-hour storm event. Discharges may occur, however, as a result of: • Evacuating sediment from ponds to regenerate the pond system's capacity to contain the design volume of runoff resulting from a 10-year 24-hour precipitation event. Sampling of discharge is required as per the General Stormwater permit and certification if ponds are evacuated and the water is to be discharged. • Overflow related to a precipitation event greater than the 10-year, 24-hour precipitation event. • Actions implemented to protect or maintain the pond systems. • Overflow related to the occurrence of multiple precipitation events that may or may not individually exceed the 10-year, 24-hour precipitation design event. 4.3.3.2 Sampling of Regenerative Release Water quality sampling will be performed for regenerative releases from the most down-gradient point of the EMPs described herein. A regenerative release may be required in the event that CC&V is unable to meet downstream water augmentation requirements by normal means. In this instance, CC&V may meet water augmentation requirements by delivering water to affected drainages by siphoning off or pumping of stormwater management ponds. If such releases occur, monitoring will be conducted as follows: Monitoring will be conducted up to twice per calendar year when regenerative releases occur. It is anticipated that such releases will not occur frequently. Such sampling will occur once between January 1 and June 30 and once between July 1 and December 31,with at least three months separating the sampling events. After sufficient characterization of the regenerative release has been accomplished, the monitoring frequency may be reduced upon concurrence from the Colorado Water Quality Control Division ("WQCD"). Regenerative release monitoring parameters are summarized in the following table: