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Slurry Wall Design Report Loloff Pit 5/24/2016 Page 12 of 16 east end of the pit. A low permeability berm of variable height will be constructed along the ramped portion of the working pad. 6.3 Slurry Wall Depth and Width Based on test boring information the total depth of the slurry wall along the alignment is estimated to range from 45 to 75 ft below the working pad elevation, with an average depth of 60 ft. The slurry wall width shall be a minimum of 3 ft. 6.4 Slurry Wall Key To minimize seepage at the base of the slurry wall, the wall shall be installed at least 4 ft into competent bedrock which exists below weathered bedrock. The estimated depth to the top of bedrock is depicted on Sheets SH-8 through SH-10 and summarized on Table IV. Localized areas with a thicker weathering profile may be present. Continuous evaluation of ground conditions during excavation shall be used to determine if a deeper key is required. 6.5 Slurry Wall Excavation The slurry wall shall be constructed using the continuous slurry trench method. The slurry trench method involves excavating a trench and stabilizing the excavation with viscous bentonite slurry. Trench stability is achieved by establishing a slurry elevation several feet above the groundwater elevation such that a positive hydrostatic slurry pressure exists in the trench and acts against the trench walls to provide stability. The slurry level shall not be allowed to drop more than 2 ft below the working platform and should be at least 4 ft above groundwater. It is anticipated that the soil and rock along the slurry wall alignment can be excavated with a specially equipped large excavator. 6.6 XCEL Power Poles Along the southwest corner of the property there are three XCEL power poles supporting 115 kV transmission electric lines. XCEL recommends a minimum clearance of 20 feet in any direction from live powerlines to construction equipment. Brierley Associates is not responsible for construction site safety. The slurry wall alignment shown is a sufficient distance from the XCEL power poles located on the property such that the power poles and slurry wall are not anticipated to interact with each other. In order to monitor the power poles during slurry wall construction, we recommend implementing the following instrumentation and monitoring program: 1. Install one survey reference point on each XCEL power pole footing and one settlement monitoring point between the XCEL power pole footing and slurry wall, 25 ft offset from the slurry wall alignment as shown on drawing sheet SH-18. 2. Survey the reference and settlement monitoring points once per day when slurry wall construction is between STA. 16+00 and STA. 31+00. Record both the elevation and horizontal position. BRIERLEY ASSOCIATES Creating Space Underground