2021-09-07_REVISION - M1973021 (4)

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Aggregate Industries, Morrison Quarry Amendment No.7 to Permit M-1973-021 FN Morrison,CO The majority of stormwater from the plant and associated mining areas will remain onsite and percolate into the ground. Control structures are used to manage and direct runoff. The following control structures are currently in use throughout the mine site: • Site Grading —The site is graded in such a way that all stormwater flows are allowed to either be collected onsite, where they will infiltrate and/or evaporate, or are directed to retention basins and/or the current mining pits. • Berms — Earthen berms are used throughout the mine site along the perimeters as a measure to contain stormwater within the site perimeter. • Stormwater Retention Basins—These ponds collect stormwater from primarily the northern and eastern portions of the property. However, in large storm events, the ponds collect water from the majority of the site. These ponds allow stormwater to settle before being discharged. The stormwater retention basins at Outfalls 001 and 003 were installed according to design plans. • Check Dams—The check dams help direct stormwater to the stormwater retention basins and slow down flow from the haul road to the retention basins. Check dams are installed and maintained according to the Colorado Department of Transportation Erosion Control Manual. • Truck Wheel Wash —The truck wheel wash area is a closed loop system that recycles wash water. Truck tires are sprayed with water as they travel through the truck wash to prevent offsite material tracking. • Temporary Dewatering Sumps and Pumps—When required, surface water that has accumulated in low points in the Central and South Quarries is pumped to Outfalls 003 or 005 for discharge. This is done through the use of mobile equipment, including sumps, pumps, and associated piping. The drainage paths for stormwater in the North, Central, and South Quarries and main access road support areas are described as follows: • North Quarry—This drainage area consists of the North Quarry and Reservoir Site 11. The North Quarry has been partially reclaimed and revegetated, and no further development is planned for this area. Runoff from this drainage reports to Reservoir Site 11. As was discussed in Exhibit E—Reclamation Plan, Planned Reclamation, the North Quarry Repository area benches and upper surfaces will be sloped to allow for surface drainage. Strip drains will be installed and water will be conveyed to onsite sedimentation basins (see Exhibit F.1) then discharge through Outfall 003. • Central Quarry—This drainage area consists of the Central Quarry, which has been partially reclaimed and revegetated, and is currently being used as a stockpile management area. Runoff from these reclaimed slopes and stockpile areas is allowed to accumulate at the Central Quarry low point. From here, it is allowed to infiltrate or is pumped to either Outfall 003 or 005 within 72 hours. Of note, the Central Quarry is currently the location where UD#1 runoff reports. This will continue until the diversion construction activities discussed above are completed. September 2021 1 49