2024-04-25_PERMIT FILE - M2024017

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Discharge from mining areas will take place within 72-HR of a storm event to prevent diversion of water rights. Discharge will be conducted via pump, weir, or pipe. The operator will sample water discharges as required by their Colo. Dept. of Public Health and Environment permits. Detaining water within active mining pods will allow for sediment to settle out and ensure clean water discharges. 6.1.2. Post Reclamation Drainage patterns for after reclamation can be seen on Map F-1. Each pod will drain as it did prior to mining. In general, this means drainage patterns will return runoff to the drainage draw between pods. Revegetation of the pods will ensure that stormwater runoff does not generate additional sediment discharges. 6.1.3. Flood Protection No mining takes places near the Colorado River or any other flooding waterway. 6.2. Disturbed Area Runoff During all stages of mining, there is enough water storage capacity to contain the 100-year 24- hour storm event and prevent erosion from surface water discharge. The expected rainfall from these events at the Lockhart Pit is provided in Table G-2 below. Table G-2 Area Storm Events (from NOAA') RainfallEvent Probability Event 100-YR 24-HR 2.33 Peak runoff for the 100-YR event was determined for premise, mine, and reclaimed conditions. Prior to mining all of the disturbed area freely drains to the drainage draws onsite. During mining, the mining pods have enough storage to contain the entire discharge from the storm event. Following reclamation, the mining pods return to freely draining in the same manner as prior to mining. Therefore, mining and reclamation will not create any additional drainage from the site. The discharge volumes from these storm events are calculated in Appendix G-1. The Exhibit C maps summarizes the drainage basins. All runoff calculations were conducted using the Rational Method as required by Grand County drainage criteria. Soil Hydrologic Group is taken from the soil report in Appendix I-1. Time of concentration is calculated from site topographic data. Storm date is from NOAA. 7. Groundwater Groundwater will not be interacted with at the Lockhart Pit. Groundwater is located over 100- feet below the bottom of the gravel deposit based on the nearest well data. While exact groundwater levels are not known from exploration and surrounding wells, groundwater is likely 'National Oceanic and Atmospheric Administration Lockhart Pit G-3 ® Lewicki&Associates March 2024