2018-02-21_REVISION - M2008017 (7)

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Derr Pit Project DRMS 112 Permit Amendment EXHIBIT G Water Information Introduction The proposed mining operation is located in the Northeast ¼ of Section 4, Township 5 North, Range 65 West, Sixth P.M., in Weld County. In terms of notable area water features, the proposed Derr Pit mining site is located 1/8 mile northeast of the Ogilvy Ditch and 3/8 miles north of the mainstem channel of the Poudre River. Approximately the southerly 30% of the proposed 145.05-acre permit area is within the current regulatory Poudre River 100-year floodplain. Specifically, the site is located within the Poudre River floodplain Zones AO and B, with 100-year flood depths of one to three feet. All work performed in the floodplain will conform to the Weld County Flood Hazard Regulations, and will be subject to a Weld County Flood Hazard Development Permit. The major 100-year floodplain accommodations at the Derr Pit operation will include:  Stockpiling of stripped and mined materials outside the 100-year floodplain to the greatest extent practical, from commencement of the operation;  Alignment of stockpiles parallel to the estimated 100-year flood flow direction;  Breaks or gaps between stockpiles to allow floodplain flows through;  No net import of materials into the 100-year floodplain on the site; and  Ultimately, placement of mined material stockpiles in the pit bottom as soon as the mine excavation area is large enough to accept them. The Derr Pit mining operation itself will consist of sand and gravel production and will impact the Poudre River in the form of depletions due to evaporation of exposed groundwater, and losses associated with mining, primarily dewatering and exported material moisture content in phases 1 – 7. The most significant groundwater feature of the operation will be construction of a slurry wall liner(s) around the perimeter of the planned mined pit(s). The slurry wall(s) are planned for construction between year two and three of mining. Mining of the Derr Pit site is anticipated to last for approximately fifteen to eighteen years. Once reclamation is complete, lined water storage reservoir(s) will be created, and will have a total surface area of approximately 66.20 acres at projected maximum water storage levels. The mining operation will extract sand and gravel deposits from the Poudre River aquifer alluvium, and will impact groundwater systems hydraulically connected to the Poudre River in Phases 1 – 7. The depth to the alluvial aquifer groundwater ranged from 8 to 17 feet in thirteen of fifteen site geotechnical borings performed across the