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and post reclamation. The primary concern for surface water protection at the site is preventing <br /> the discharge of sediment, oil, and/or hydraulic fluids from the operation areas. Oils and <br /> hydraulic fluids are stored on site following the standard best management practices. These <br /> practices include the use of secondary containment at fluid storage and transfer points, spill kits, <br /> and employee training regarding safe handling practices. Sediment is trapped onsite using <br /> controls and best management practices by directing and controlling surface water runoff that <br /> enters the disturbed areas. More information on sediment and surface water control is provided <br /> below. <br /> 6.1 . Surface Water Handling <br /> Pre-mining, stormwater flows and is carried off site in the Big Sandy Creek. Reclamation will <br /> return the flows to their pre-mining conditions, to drain towards the Big Sandy Creek in the <br /> center of the site. <br /> 6.1.1. Mining <br /> All stormwater from disturbed areas will either be contained in the pit or within stormwater <br /> bermed areas. <br /> 6.1.2. Post Reclamation <br /> The drainage patterns during mining will be retained following reclamation of the site. Any <br /> surface water runoff will collect in the reclaimed reservoir. There is enough storage capacity <br /> above the anticipated reservoir level and the top of the shore to store the 100-year storm <br /> events. More on those calculations are provided in section 6.2 below. <br /> 6.2. Disturbed Area Runoff <br /> During all stages of mining, there is enough water storage capacity to contain the 5-year and <br /> 100-year 24-hour storm events and prevent erosion from surface water discharge. The <br /> expected rainfall from these events at the Limon Sand and Gravel Site is provided in Table G-2 <br /> below. <br /> Table G-2. Area Storm Events (from NOAA1) <br /> Event Probability Event Rainfall <br /> (inches) <br /> 100-YR 24-HR 4.84 <br /> The peak runoff was generated from these values for the various drainage basins during all <br /> stages of mining. Pre-mine, mining, and reclamation conditions are delineated on the Drainage <br /> Map. The discharge volumes from these storm events are calculated in Appendix G-1 at the end <br /> of this exhibit. Table G-3 summarizes the runoff volumes and storage volumes for each <br /> drainage. All drainage calculations were made using the Rational Method identified in the Mile <br /> High Flood Control District. <br /> National Oceanic and Atmospheric Administration <br /> Limon Sand& Gravel Pit <br /> Lewicki&Associates <br /> August 2024 <br />