2011-08-01_REVISION - M1978210 (15)

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5.7 Slurry Wall Working Platform Slurry wall construction shall occur on a stable and flat working platform from which excavation, backfill mixing, and backfill placement can occur. Sheet C -012 shows the working platform configuration that is required for mixing of the SB backfill along the side of the trench. Along the alignment, the working platform shall be constructed with a maximum 1.0 percent grade along the alignment. Portions of the alignment which require cuts or fills are indicated on sheets C -009 through C -011. Construction of the slurry wall working platform is being done by Hall Irwin. 5.8 Construction Water Water for construction activities including slurry and backfill mixing shall be on -site pond water or groundwater permitted for construction use. 5.9 Slurry Wall Cap Upon completion of slurry wall construction, a protective cap shall be constructed on top of the slurry wall, as shown on Sheet C -012. This cap shall consist of a 2 -ft thick layer of granular material placed over the top of the slurry wall as shown. C -013 shows the traffic cap that will be constructed in the areas where Weld County vehicles will travel over the slurry wall. 5.10 Site Reclamation After completing backfill placement, areas disturbed by construction shall be cleaned of all debris, excess excavation material, and excess slurry. The ground surface will be brought back the pre - construction grades by use of on -site materials and the exisiting ground surface shown in sheets C -009 through C -011. In order to maintain the integrity of the slurry wall, the mine operator should adhere to the excavation considerations presented below. 5.11 Temporary Excavation Slope Considerations After installation of the SB slurry wall, the crest of any temporary excavation slopes required for gravel mining shall be offset a minimum of 25 ft from the slurry wall. The temporary excavation slopes shall be 3H:1 V or flatter, as shown on Sheet C -012. Mining closer to the slurry wall than the limits described herein may jeopardize the stability of the slurry wall. It is possible that a smaller offset or steeper slope could be used if demonstrated by a stability analysis. 5.12 Quality Control Sampling and Testing Lyman Henn will perform the sampling and testing of backfill materials according to the methods and frequencies specified below. Sampling and testing will be performed by personnel experienced in conducting the type of test required. Samples will be representative of the overall volume of material from which the sample is taken. Equipment for sampling and testing shall be in good condition. Equipment shall be set up for testing and tests will be performed at the site unless otherwise specified. Test results will be reported in an as -built report. Lyman Henn will be responsible for representative, quality, and accurate sampling and testing. G:\PROJECTS \111025 Geisert Gravel Pit Slurry Wall\O \01 \Geisert Slurry Wall Design Repon.doc 10