2018-10-22_REVISION - M2008078 (13)

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CESARE,INC. The Seep/W analysis with a slurry wall with a hydraulic conductivity of 1x10"' cm/sec provided a total flux (i.e., flow) in a one-foot length of wall of 0.62973 ft3/day as shown in Figure 2. For this case, we estimated total inflow through the bottom and the perimeter of 2,808 fe/day. The State Engineer's total maximum allowable inflow (bottom and perimeter) is 28,767 ft3/day. Based on the material properties used, for the section analyzed with the thickest gravel layer, the factor of safety is about 10 — between the actual calculated inflow and the total maximum allowable inflow. We recommend that the slurry wall, when installed, have a minimum hydraulic conductivity of 1x10"7 cm/sec. SLOPE STABILITY DURING RAPID DRAWDOWN For the slope stability analysis during rapid drawdown, both the section with the thickest gravel layer and the section with the thickest clay layer were analyzed using Seep/W and Slope/W. Rapid drawdown of the reservoir was analyzed with a drawdown rate of 1 foot per day. Pore pressures were computed using transient seepage analysis. Slope stability analyses were performed during drawdown which generated a minimum factor of safety versus time plot. The cross sections and results for the gravel section are shown in Figure 3 and the results for the clay section are shown in Figure 4. The minimum factor of safety versus time plots are shown in Figures 5 and 6, for the gravel section and clay section respectively. The minimum factor of safety was 1.74 for the gravel section and 1.70 for the clay section during rapid drawdown. A sensitivity analysis was performed by lowering the cohesion in the clay from 100 psf to 50 psf. The analyses shown in Figures 3 through 6 included a clay cohesion of 100 psf. The minimum factor of safety versus time plot with a clay cohesion of 50 psf is shown in Figures 7 and 8, for the gravel section and clay section respectively. The minimum factor of safety was 1.68 in the thick gravel section and 1.58 in the thick clay section. A sensitivity analysis was performed on the weathered shale bedrock by varying the friction angle from 27 degrees to 21 degrees. The results of this sensitivity analysis are shown in Table 4. TABLE 4. Results of Sensitivity Analysis for Weathered Shale Bedrock Friction Angle Iwlinirl>l O FAd1ot of Safety During Rapid pmwdown (41e1taw) 71MIck Gmel<Section I Thick Clay Section 27 1.74 1.70 26 1.70 1.70 25 1.66 1.70 24 1.62 1.67 23 1.57 1.62 22 1.53 1.59 21 1.48 1.55 The slope stability analyses performed show that both the thick gravel section and thick clay section are stable during rapid drawdown of the reservoir. 11.124 GP Ranches Memo 03.21.1303.21.13 4