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Windsor East Mine, Exhibit G – Water Information September 2022 <br /> Page 2 | 11 <br />The Windsor East site is underlain by two aquifers: <br /> The valley-fill deposits of the Lower Cache la Poudre River. <br />o described in: Hershey, L.A . and PA. Schneider, 1972. “Geologic Map of the Lower Cache la <br />Poudre River Basin, North-Central Colorado", USGS Miscellaneous Geologic Investigations <br />Map I-687. (See Figure G-2) <br /> The Fox Hills Sandstone <br />o described in: Robson, S.G. 1989, “Alluvial and Bedrock Aquifers of the Denver basin – <br />Eastern Colorado’s Dual Ground-Water Resource”, USGS Water-Supply Paper 2302 <br />(c) Submit a brief statement or plan showing how water from de-watering operations or from runoff from <br />disturbed areas, piled material and operating surfaces will be managed to protect against pollution of <br />either surface or groundwater (and, where applicable, control pollution in a manner that is consistent with <br />water quality discharge permits), both during and after the operation. <br />The geologic conceptual model of the subsurface and groundwater was developed from the geologic map for the <br />area and the boring logs associated with the installation of the monitoring well network at the Windsor East site and <br />the Parsons Mine site located to the east (Figure G-3). Based on water levels measured in these wells, a <br />groundwater level elevation map was developed (Figure G-5). Following removal and stockpiling of topsoil, each of <br />the four cells will be dewatered and mined. Sand and gravel will be extracted using the “dry” mining method in which <br />the water table is lowered to allow mining to be performed under drained conditions. To lower the water table, local <br />dewatering is conducted using a perimeter drain constructed around each planned mining cell. <br />The dewatering system would discharge to the Cache la Poudre River. Dewatering of the mine would lower the <br />groundwater levels to a limited extent in the surrounding alluvial aquifer and will not impact the underlying Fox <br />Hills Sandstone aquifer. Effects on groundwater levels are projected to be limited in extent due to natural and <br />manmade hydrologic and hydrogeologic characteristics and boundaries, principally including the transmissive <br />nature of the alluvial aquifer, the Cache la Poudre River, and the mining operation. Figure G-6 illustrates resulting <br />changes to groundwater flow directions during mining and after reclamation. <br />The available gravel resource is anticipated to be mined for approximately 6 years; however, the rate of mining <br />and overall life of the mine is dependent upon demand and market conditions. All material mined at Windsor East <br />will be conveyed to Martin Marietta’s adjacent Parsons Mine site for processing at the existing plant on that site. <br />Upon completion of mining, the reclamation plan for the mine includes the emplacement of compacted clay <br />embankment liners in Mining cells A and C, while cells B and D will be backfilled. These cells will thereby be <br />converted to sealed water storage reservoirs, which will be owned and used by GWIP, LLC, the landowner of the <br />Windsor East Mine site. <br />Exhibit D: Pre-Mining and Mining Plan shows the location of the Affected Area and proposed mining cells. <br />Changes to the hydrologic balance within the Affected Area will be limited to the localized dewatering associated <br />with the excavation of the mine cells, and the minor alteration of the existing groundwater flow patterns due to the <br />subsequent installation of compacted clay embankment liners during reclamation. Figures G-5 and G-6 show the <br />mine cells and conceptual groundwater flows before and after the installation of the compacted clay liners. <br />1.1 HISTORIC USE <br />The Windsor East property has historically been used for agriculture. The adjacent neighbors include Martin <br />Marietta’s Parsons Mine site to the east, agricultural land with a few residences to the north and west, and the <br />Cache la Poudre River to the south. <br />Based on well registration, land use besides agriculture within two miles of the site has included Eastman Kodak <br />to the west and northwest, Front Range Energy to the northwest of the site, Joseph Energy to the northwest of the <br />site, and Hensel Phelps Construction to the northwest of the site. <br />