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Wattenberg Mine, Exhibit G—Water Information May 2023 Please see Exhibit C Pre-Mining Maps for the location of all tributary watercourses, wells, springs, stock water ponds, reservoirs, and ditches on the affected land and on adjacent lands where such structures may be affected by the proposed mining operations. (b) Identify all known aquifers The Wattenberg Lakes site is underlain by multiple aquifers: • The alluvial deposits Post-Piney Creek Alluvium and Piney Creek Alluvium of the South Platte River. o described in: Colton, Roger B., 1976. "Geologic Map of the Boulder-Fort Collins-Greeley area, Colorado", USGS Miscellaneous Geologic Investigations Map 1-855-G. (See Figure G- 2) • The Lower Arapaho Aquifer o described in: Robson, S.G. 1989, "Alluvial and Bedrock Aquifers of the Denver basin— Eastern Colorado's Dual Ground-Water Resource", USGS Water-Supply Paper 2302 • The Laramie-Fox Hills Aquifer o described in: Robson, S.G. 1989, "Alluvial and Bedrock Aquifers of the Denver basin— Eastern Colorado's Dual Ground-Water Resource", USGS Water-Supply Paper 2302 (c) Submit a brief statement or plan showing how water from de-watering operations or from runoff from disturbed areas, piled material and operating surfaces will be managed to protect against pollution of either surface or groundwater(and, where applicable, control pollution in a manner that is consistent with water quality discharge permits), both during and after the operation. The conceptual model of the subsurface geology and groundwater flow was developed from the geologic map for the area and the subsurface conditions observed during the installation of the monitoring well network at the Wattenberg Lakes site(Figure G-3). Based on water levels measured in these wells, groundwater elevation maps were developed for both low-water conditions associated with the winter non-irrigation season and conditions that exist at the end of the irrigation season in August(Figures G-4 and G-5, respectively). Figures G-4 and G-5 indicate a northeasterly flow direction that becomes flatter and more northerly as the water crosses the site. Figure G-4 groundwater contours show the impacts of the recent and current Struck Pond dewatering,where this water is sent to the Stillwater Ski Lake. There will be minimal additional mining activities, limited to within the Struck Pond area; changes to current land surfaces will be primarily due to reclamation activities as outlined in Exhibit E. Pond 3 currently has a slurry wall, constructed in 2013, which influences groundwater flow in the immediate vicinity. The planned Struck Pond expansion will involve dewatering prior to and during mining. Shallow groundwater flow will be impacted during dewatering activities associated with the expansion although these impacts are expected to be limited to the aquifer only around this area. Due to the permeability contrast between the gravel aquifer and the bedrock beneath it, hydraulic changes due to mining will not impact the underlying Laramie-Fox Hills aquifer. Effects on groundwater levels are projected to be limited in extent due to natural and manmade hydrologic and hydrogeologic characteristics and boundaries, principally including the transmissive nature of the alluvial aquifer, the nearby South Platte River, and the minimal additional mining operations. The reclamation plan for the mine includes the placement of a slurry wall and perimeter drain around the Struck Pond. The Struck Pond will then be used as water storage for the City of Westminster. Changes to the hydrologic balance in the area will be limited to minor, localized alterations of the existing groundwater flow patterns due to the slurry wall. 2.0 HISTORIC USE The Wattenberg Lakes property has been used for mining since the Colorado Division of Reclamation, Mining and Safety (DRMS) issued the original permit in 2004. The reclaimed Parker-Dersham aggregate mine and pond, with slurry wall around it, lies to the south of the property, as does the Stillwater Ski Lake, which is man-made and unlined. Agricultural lands exist to the west of the site. Additional aggregate mines and industrial operations occur across the South Platte River to the east. OTETRA TECH P a g e 2 1 8