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CESARE, INC. <br />The Seep /W analysis with a slurry wall with a hydraulic conductivity of 1x10 "' cm /sec provided a <br />total flux (i.e., flow) in a one -foot length of wall of 0.62973 ft3 /day as shown in Figure 2. For this <br />case, we estimated total inflow through the bottom and the perimeter of 2,808 fe /day. The State <br />Engineer's total maximum allowable inflow (bottom and perimeter) is 28,767 ft3 /day. Based on the <br />material properties used, for the section analyzed with the thickest gravel layer, the factor of safety <br />is about 10 — between the actual calculated inflow and the total maximum allowable inflow. We <br />recommend that the slurry wall, when installed, have a minimum hydraulic conductivity of 1x10 -7 <br />cm /sec. <br />SLOPE STABILM DURING RAPID DRAWDOWN <br />For the slope stability analysis during rapid drawdown, both the section with the thickest gravel <br />layer and the section with the thickest clay layer were analyzed using Seep /W and Slope/W. Rapid <br />drawdown of the reservoir was analyzed with a drawdown rate of 1 foot per day. Pore pressures <br />were computed using transient seepage analysis. Slope stability analyses were performed during <br />drawdown which generated a minimum factor of safety versus time plot. The cross sections and <br />results for the gravel section are shown in Figure 3 and the results for the clay section are shown in <br />Figure 4. The minimum factor of safety versus time plots are shown in Figures 5 and 6, for the <br />gravel section and clay section respectively. The minimum factor of safety was 1.74 for the gravel <br />section and 1.70 for the clay section during rapid drawdown. <br />A sensitivity analysis was performed by lowering the cohesion in the clay from 100 psf to 50 psf. <br />The analyses shown in Figures 3 through 6 included a clay cohesion of 100 psf. The minimum <br />factor of safety versus time plot with a clay cohesion of 50 psf is shown in Figures 7 and 8, for the <br />gravel section and clay section respectively. The minimum factor of safety was 1.68 in the thick <br />gravel section and 1.58 in the thick clay section. <br />A sensitivity analysis was performed on the weathered shale bedrock by varying the friction angle <br />from 27 degrees to 21 degrees. The results of this sensitivity analysis are shown in Table 4. <br />TABLE 4. Results of Sensitivity Analysis for Weathered Shale Bedrock <br />Friction Angle Minimum Factor of Safety During Rapid'' <br />+� Drawdown ' <br />(degrees) 1 Thick Gravel Section Thick Clay Section <br />27 1.74 1.70 — <br />26 1.70 1.70 <br />25 <br />1.66 <br />24 <br />1.62 <br />23 <br />22 <br />21 <br />1.57 <br />1.53 <br />1.48 <br />The slope stability analyses performed show that both the thick gravel section and thick clay <br />section are stable during rapid drawdown of the reservoir. <br />11.124 GP Ranches Memo 43.21.1303.21.13 4 <br />