2004-05-20_REVISION - M2000158 (2)

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Mr. Dennis Dubbet -2- May 14, 2004 • Phase 2 will consist ofconstructing asoil-bentonite trench around the perimeter of Sharkey Lake with subsequent removal of the tnined deposits and creation of a water storage reservoir. We also understand that the removed material will be temporarily stockpiled between the east side of the two lakes and the Western Mutual Ditch. Ultimately the stockpiled materials will be transported to the Platte Sand and Gravel processing plant located south of Sharkey Lake. The location of the lakes and the general alignment of the soil-bentonite trenches are shown on Figure 1. Although other lakes maybe constructed in the future using similar technologies, impacts from the other lakes were net considered in this evaluation. Evaluation This evaluation was based on the following: • Observations made during the site visit. • Regional USGS groundwater information obtained from the Geohydrology of the Shallow Aquifers in the Fort Lupton-Gilcrest Area, Colorado, S.G. Robson, J.S. Heiny, and L.R. Arnold, 2000. • USGS 7.5 Minute Topographic Quadrangle Maps. Groundwater elevations in nearby alluvial wells obtained from the Office of the State Engineer, Division of Water Resources, permitted wells data. • Geotechnical borings and groundwater depths from a CTL Thompson, Inc. letter repoR dated August 1, 2001. • Our experience with soil-bentonite trenches, sand and gravel mines, and lined water storage reservoirs. The topography at the site generally slopes from south to north with about ] 0 feet in elevation drop across the site, which is a slope of about 3 percent. The proposed gravel mines (lakes) are between the east bank of the South Platte River and the Western Mutual Ditch, and generally within an inside bend in the South Platte River. The invert of the ditch is approximately 10 to 15 feet above the ground surface elevation along the east side of the proposed gravel pits as shown in Photos 1 and 2, attached. The ditch appears to be unlined, however seepage was not observed exiting on the west slope of the ditch. It is our understanding Platte Sand and Gravel owns the property from the river to about the west side of the ditch. The depth to groundwater generally varies from 4 to 8 feet below the ground surface. Groundwater appears to be at about 4 feet below the ground surface near the south edge of Sharkey Lake, at about b feet below ground surface at the north side of Sharkey Lake, and at about 8 feet below ground surface at the north end of Longhom Lake. In general, the distance between the ground surface and groundwater increases from south to north. Based on available data, regional groundwater flow is generally from the south-southeast toward the South Platte River at a gradient of about 0.0021 ft/ft as shown on Figure 2. The gradient was V ~0119J Longhom and Shulry Iake~0919I W-OS-Q Preliminary Growdwarrr Evalualiorve.Joc