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<br />~ ' the length of ] 670 feet, a width of 3 feet, and a depth of 50 feet, approximately 9280 cyds of <br />slurry wall will be installed. Approximately 50% of the wall material will be backfill <br />~ ' material consisting of the soil/slurry mixture. Therefore, approximately 4640 cyds of either <br />screened on-site or off-site borrow material will be required for construction of the slurry <br />' wall. <br />' During slurry wall installation, water supply will be required. This water w 11 be obtained <br />from a combination of either M-17, BF-1, BF-3, BF-4, or BF-5 at a maximurl nominal rate <br />of approximately 400 gpm. <br />' 3.1 Hydrology <br />Minimizing the rate of inflow from the Rito Seco alluvium would be beneficial in that the <br />' total rate of inflow to the West Pit (approximately 80 gpm, Section 3.1.4.4 of fR-26) would <br />decrease. Therefore, after placement of the slurry wall the sources of water flow into the <br />West Pi[ would be restricted to Precambrian bedrock flow and limited .nfiltration of <br />precipitation through the backfill (Figure 3). The decrease in the rate of groundwater inflow <br />' would translate directly into along-term reduction in the volume of water that ~NOUId need to <br />be managed to maintain the tazget water level in the West Pit as described in TR-2b. <br />' Placement of the slurry wall would not constitute a final solution to hydrologic: flows in the <br />' vicinity of the West Pit because the modification to the naturally open hydrologic system <br />imposed by the slurry wall would not control all of the governing hydrologic: flows. The <br />' hillside to the north of the West Pit represents the recharge zone that contributes to the inflow <br />of Precambrian bedrock groundwater to the West Pit. Water levels measured in Precambrian <br />' well PC-1 indicate that there is sufficient potential hydraulic head in the Precambrian <br />bedrock aquifer to cause the water level in the West Pit [o increase sufficien[l,~ to intercept <br />' the land surface if a slurry wall was installed and no other hydrologic controls were <br />instituted. Thus, an artificial outflow of water from the West Pit must be provided to <br />' maintain steady-state hydrologic conditions in the overall system (recharge zone to outflow). <br />' Therefore, some form of water level control would also have to be implemented in order to <br />control the water level elevation in the West Pit. From the standpoint of water level control, <br />' Bae/e Moanmrn Resources, lnc. Srtepherd Miller, lnc. <br />P:IleeT6%L1'7u.ryN'dlUhrignnpvrr 3Z S Nmem6er 5, /999 <br />