2021-04-20_REVISION - M1983033 (20)

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Walstrum Spur Amendment, Exhibit G— Water Information 1.0 RESULTS AND CONCLUSION April 2021 The results of our water investigations in and around the existing Walstrum Quarry (Existing Quarry) and the Spur Amendment Area (Spur Amendment), as presented below, support the following conclusions: • The Spur Amendment, located east of the Existing Quarry, is underlain by Precambrian metamorphic rocks with very low intrinsic permeability. • The site receives approximately 16 inches of precipitation per year. The vast majority of the precipitation that falls on the Spur Amendment runs off due to the steep slopes and low permeability of the bedrock. • Detailed hydrogeologic reconnaissance of the Spur Amendment and surrounding environment did not identify any springs or seeps. • Given the steepness of the land surface and very low permeability of the bedrock, there is very little groundwater recharge in the Spur Amendment. What little recharge may occur under pre-mining conditions through fractures in the bedrock will continue through the life of the quarry and after reclamation. The fact that the Existing Quarry is a dry operation and water used at the mine is withdrawn from Clear Creek under decree 98CW473 provides additional evidence that mining operations in the Existing Quarry and Spur Amendment will not have a material impact on the hydrologic balance. • The Spur Amendment is located east of the Colorado Mineral Belt. Core samples were analyzed for acid- base accounting, metals, and leachability. The results of the analyses demonstrate that the quarry will not represent a geochemical risk to the environment. • The Spur Amendment occupies a topographic high and is surrounded by hydrogeologically and topographically low areas represented by the Existing Quarry, Clear Creek, North Clear Creek, and an unnamed tributary (the Tributary) to North Clear Creek. These features prevent groundwater from flowing onto or through (via underFlow) the Spur Amendment east or south of the Existing Quarry. Furthermore, the base of the excavation is above the elevation of Clear Creek and North Clear Creek. Consequently, the Spur Amendment is hydrogeologically isolated from the surrounding groundwater regime. • Based on the above information and the information in this Exhibit, it can be concluded that off-site groundwater wells and off-site surface water will not be impacted by mining the Spur Amendment. 2.0 INTRODUCTION This Exhibit presents an assessment of the Spur Amendment pre-mining hydrologic balance and demonstrates why the proposed amendment will not have a material impact on the hydrologic balance. This Exhibit presents information gathered from on-site physiography; precipitation, temperature, and runoff; geology (stratigraphy and structure); and groundwater (hydrogeologic reconnaissance) as the basis for this assessment. A review of the available published reports and information in Albert Frei & Sons, Inc. (AFS) files was conducted to form an initial understanding of the site hydrologic conditions. Figure G-1 presents the site location map of the proposed Spur Amendment. Figure G-2 is a composite of the two USGS geologic maps of the area (USGS 1975 and 1976). Figure G-3 depicts geologic cross sections of the Spur Amendment. The geometry of the proposed pit for the Spur Amendment is shown on the cross sections. Notable hydrogeologic characteristics of the Spur Amendment are that the excavation does not cross the surface drainage divides and the base of the quarry is at an elevation of 7,240 feet which is above the elevation of Clear Creek. Figure G-4 presents the land surface slopes in the Spur Amendment. The baseline data review process identified several data needs related to the nature of the geology and groundwater conditions at the Site. Field investigations were performed to fill these identified data needs. Field studies conducted as part of the data gap resolution included: A hydrogeological reconnaissance investigation was conducted during June and September 2020. The reconnaissance was implemented to address groundwater conditions in unconsolidated sediment and the bedrock to understand the hydrologic balance, specifically to identify seeps, springs, and water supply wells that may be present in the proposed Spur Amendment. Figure G-5 presents the location of photographs OTETRA TECH P a g e � I 7