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Mr. Gazy Curtiss Division of Minerals and Geology December 29, 1997 Page 3 7.) The wash pond will not be lined, as initially thought, and will be used as a settling pond for the sand and gravel washing operation, not asphalt production. The settling pond will be created during the construction of the slurry wall and supplied with water from an adjacent well (see substitute supply plan). The pond water will be re- circulated and clay and silt from on-site material processing will seal the pond. This clay liner will provide a barrier between the pond and the groundwater. A slurry wall will enclose Phases 2 and 3 (see Exhibits C and F) and will be constructed prior to the mining of these phases. Groundwater quality will be maintained since no toxic or hazardous materials will be used in any of the processing on-site. The slurry wall will also encircle the mining operation, creating a barrier between the mining areas and the groundwater. No flocculants will be used. 8J The slurry wall is made of a bentonite and fines mixture and will be constructed to a depth of 35 to 45 feet. The wall will be keyed into a claystone and clay/sandstone bedrock for two to four feet. Both the claystone and fine-grained sandstone have low permeability and are suitable for reservoirs. The type of bedrock was determined by 18 bore samples, which were analyzed prior to starting the project. The groundwater flows to the northeast, toward the river. With the introduction of the slurry wall, the groundwater will flow around the wall and then continue in its' predetermined path. The gradient flow of the groundwater was determined from water contours of the 1968 Brighton Reach of the South Platte River Valley map. 9.) On-site processing equipment will gradually be moved off-site as mining comes to an end. When only five to ten acres in [he processing area remain on-site, this material will be removed as a raw product. 10.) Above ground fuel tanks will be used on-site. Spill prevention measures used for these tanks include a bernr enclosure that is equal to the volume of the tanks. The tanks are temporary and movable and the demolition and disposal of the berm is taken into consideration in Exhibit L under F (8). 11.) The substitute supply plan application for Phases 2 and 3 will be delivered to your office on Wednesday December 30, 1997.