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6.1.1. Mining <br /> During all pods of mining, and for each drainage basin, surface water runoff will drain to the <br /> active mining pit. Map C-2 shows the anticipated drainage patterns during mining. Grading of <br /> the site to drain internally ensures that no sediment laden water flows enter the river or any <br /> other natural waterways. There is more than enough storage within the pits to contain the 100-yr <br /> storm and smaller events. Stormwater control measures in the form of berms and sumps will be <br /> implemented in all disturbed areas to prevent the uncontrolled discharge of stormwater. NPDES <br /> discharge outfalls will be permitted at each mining pod to accommodate discharge control. <br /> Discharge from mining areas will take place within 72-HR of a storm event to prevent diversion <br /> of water rights. Discharge will be conducted via pump, weir, or pipe. United Companies will <br /> sample water discharges as required by their Colo. Dept. of Public Health and Environment <br /> permits. Detaining water within active mining pods will allow for sediment to settle out and <br /> ensure clean water discharges. <br /> 6.1.2. Post Reclamation <br /> Drainage patterns for after reclamation can be seen on Map F-1. Each pod will drain as it did <br /> prior to mining. In general, this means drainage patterns will return runoff to the wetland laden <br /> drainage draws between pods. Revegetation of the pods will ensure that stormwater runoff does <br /> not generate additional sediment discharges. <br /> 6.1.3. Flood Protection <br /> No mining takes places near the Yampa River or any other flooding waterway. <br /> 6.2. Disturbed Area Runoff <br /> During all stages of mining, there is enough water storage capacity to contain the 100-year 24- <br /> hour storm event and prevent erosion from surface water discharge. The expected rainfall from <br /> these events at the Hayden Gravel Pit is provided in Table G-2 below. <br /> Table G-2 Area Storm Events (from NOAA') <br /> ProbabilityEvent <br /> 100-YR 24-HR j 2.65 <br /> The peak runoff was generated from these values for the three drainage basins during all <br /> stages of mining. Prior to mining all of the disturbed area freely drains to the drainage draws <br /> onsite. During mining, the mining pods have enough storage to contain the entire discharge <br /> from the storm event. Following reclamation, the mining pods return to freely draining in the <br /> same manner as prior to mining. Therefore, mining and reclamation will not create any <br /> additional drainage from the site. <br /> National Oceanic and Atmospheric Administration <br /> Hayden Gravel Pit <br /> December 2022 G-3 Lewicki&Associates <br />