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Mr. Dave Nettles, P.E. <br />February 13, 2006 <br />Page 2 <br />EXISTING CONDITIONS <br />The south cell of the Brannan #29 Pit has been partially mined. Approximately the upper 20 feet <br />of sand and gravel has been removed from the south cell. This leaves 15 to 45 feet of aggregate <br />yet to be mined. Mined materials have been hauled out of the south cell for processing in the <br />north cell. <br />There is still some gravel mining on-going in the south cell. Aggregate removal is limited to <br />above the water level, however, and this should not affect the leak test procedure. At the present <br />time, the water level in the south cell has been drawn down below the natural groundwater level <br />in the surrounding alluvium outside the slurry wall liner. As shown on Figure 1, three sets of <br />two monitoring wells have been installed around the south cell. These wells were installed to <br />monitor groundwater levels inside and outside of the slurry wall. <br />The water table inside of the south cell is currently being pumped down, with the goal of <br />lowering the water surface to a level beneath the current sand and gravel surface. The leak test <br />can then be conducted in accordance with the State's guidelines for unmined pits. <br />LEAK TEST PLAN <br />The major components for the leak test are shown graphically on Figure 1. A metered pump will <br />be set in a sump at the northeast corner of the cell. The sump will be provided with a gage rod to <br />accurately monitor the water level in the sump. Prior to the start of the 90-day test period, the <br />water level inside the cell will be pumped down to provide a minimum elevation differential of <br />10 feet between the groundwater levels on each side of the slurry wall. After pumping the cell <br />down to a reduced level, the pump will be provided with a swing arm float switch to maintain the <br />level in the sump between narrow limits on the staff gage. Pump discharges will be metered and <br />recorded throughout the 90-day test period. <br />In order to keep track of precipitation falling within the cell, a rain gage will be maintained in the <br />sump area and precipitation recorded daily. Snow fall will be measured at the site, and snow <br />moisture content estimated based on local weather station data. Evaporation from exposed water <br />surfaces within the cell will be calculated based on NOAA Technical Report NWS33 and the <br />surveyed exposed water surface area. The form we plan to use for the daily monitoring is <br />provided in Attachment A. <br />There are also three sets of paired monitoring wells around the perimeter of the cell. One well of <br />each set (MW-IIN, MW-21N, MW-311) was installed inside the slurry wall. The second well in <br />each set (MW-1 OUT, MW-20UT, and MW-30UT) were installed outside the slurry wall. The <br />water levels in these monitoring wells will be monitored weekly throughout the test duration to <br />document the hydraulic gradient across the slurry wall.