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Cripple Creek & Victor Gold Mining Company September 2, 2004 <br />Mr. Kevin Rilev -2- 043-2251 <br />Surface Water Diversion <br />The watershed reporting to the modified VLF boundary is very small (less than 4.5 acres, including <br />the proposed azea), therefore no new diversion structures will be required. Surface water run-on into <br />the modified VLF liner area will be controlled due to the presence of an existing drainage Swale <br />located along the west side of the existing access road (see Drawing Nos. 2 and 3). Storm water will <br />be routed along the existing diversion Swale and directed into the existing diversion channel, located <br />to the southwest of the modified area. The existing drainage features aze designed for the 100-year, <br />24-how storm event. <br />Slope Stability <br />Ore stacked within the modified Amendment No. 7 VLF area will be stacked to an overall slope of <br />' 1.6 Horizontal (H):1 Vertical (V), which is consistent with Amendment No. 8. A slope stability <br />analysis was conducted to include the proposed area, and is presented in Attachment B. For this <br />study, stability analyses were conducted using SLIDE version 5.0 (Rocscience 2003), a commercially- <br />' avai-able computer program, with the input parameters presented in this section. Slope stability was <br />evaluated according to the Spencer's Method of Analysis (Spencer's Method). <br />' The slope stability analyses included both static and dynamic load conditions. The dynamic loads <br />were simulated using the pseudo-static approach (Hynes and Franklin, 1984). For the pseudo-static <br />analyses, a conservative design coefficient of 0.14g (which is equal to the approved Peak Ground <br />Acceleration [PGA] for the Cresson Project) was used in the slope stability models, which is <br />consistent with that used for Amendment No. 8. <br />The slope stability analysis was based on the following parameters and assumptions: <br />1 • Crushed Ore: For the stability analysis, the crushed ore material was modeled with an angle <br />of internal friction of 40 degrees with no cohesion, based upon testing performed on Cresson <br />' ore material. The in-place net density of the material is modeled at 110 pcf, consistent with <br />that submitted previously to the Office of Mined Land Reclamation (OMLR). <br />• Composite Liner: The interface shear strength of the composite liner is based on previous <br />' testing results (presented in Amendment No. 8), and summazized as follows: <br />1. Phase II: A 1-foot-thick layer of bentonite amended SLF overlain by an <br />' 80-mil single-sided textwed LLDPE geomembrane liner, representing the <br />material used as the composite liner for Phase II. An angle of internal <br />friction of 15 degrees and 1,590 psf cohesion was used in the analysis, <br />' corresponding to the residual shear strength measwed from the interface <br />shear strength testing, consistent with that submitted previously to CC&V. <br />2. Phase III: A 1-foot-thick layer of clay borrow SLF overlain by an 80-mil <br />' single-sided textured LLDPE geomembrane liner, representing the material <br />used as the composite liner for Phase III. Based on interface shear testing <br />completed for Phase III, the shear strength of the composite liner has a <br />' friction angle of 18 degrees and no cohesion, which was used in the stability <br />analysis. <br />3. Modified VLF: A 1-foot-thick layer of clay borrow SLF overlain by an 80-mil <br />or 100-mil textured LLDPE geomembrane liner. Based on interface shear <br />testing conducted for Amendment No. 8, a friction angle of 18 degrees and no <br />1 I:\04\2251WIOOU1odAm)-0902W\0432251.0100.09]2MOdAmR090204.docGOlder Associates <br />