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July 23, 1998 -3- 983-2348.160 <br />1 in the Phase I area was conservatively modeled as having an angle of <br />internal friction of 21 degrees and no cohesion. <br />' 2. A 1-foot-thick layer of bentonite amended Soil Liner Fill overlain by a <br />80-mil single-sided textured LLDPE geomembrane liner, representing <br />' the material used as the composite liner for Phase II. Interface direct <br />shear testing results were presented to the OMLR by CC&V in a July 8, <br />1996 letter titled "Cresson Project; Permit M-80-244: Bentonite Addition <br />' to Soil Liner Fill -Stability Analysis File ". A copy of this information <br />was formally transmitted to CC&V by Golder in a July 15, 1996 letter <br />' titled "Test Results For Bentorsite Amended Soil Liner Fi[[". An angle of <br />internal friction of 15 degrees and 1,600 psf cohesion were used th the <br />analysis, corresponding to the residual shear strength measured as part of <br />' the interface shear strength testing, which is consistent with that <br />submitted previously to CC&V. <br /> <br />1 <br /> <br /> <br />1 <br />1 <br />1 <br />1 <br />1 <br />t <br />1 <br />Underdrain Geosynthetics: The underdrain consists of the following configuration (from <br />bottom to top): (1) 3-inch minus Select Structural Fill; (2) 12 oz./sq. yd. nonwoven <br />geotextile; (3) 80-mil textured LLDPE geomembrane; and, (4) 3-inch minus Select Structural <br />Fill. In Golder's January 18, 1994 Responses To Technical Reviewer, Golder referenced a <br />residual interface shear strength of 14 degrees between the textured HDPE/nonwoven <br />geotextile used in the Pregnant Pond geomembrane configuration, which was based on <br />Byrne (Design Issues With Strain Softening Interfaces In Landfill Liners, 1994). <br />Therefore, a 14-degree interface was used in the stability analyses. <br />Foundation Material: For the stability model, the subgrade was assumed to consist of either <br />competent bedrock, clean and granular native soils, or Structural Fill. These materials <br />generally have shear strengths similar to or greater than the ore materials which will be <br />overlying the liner. Therefore, the foundation material was modeled with an angle of internal <br />friction of 40 degrees and no cohesion. <br />The following table summarizes the soil parameters used in the stability model: <br />Soil:or!3nferface::!:<::::'.`.:":` `'::":'::::< :':_ ? 'le:of•Interiat;l{rietion:: ::Cttiliesiito: <br />..:.........:......:.....:.:.....::.::.......:.::.:.....:..: ...:....::..:..:.::..:...d <br />Crushed Ore 40 0 <br />Smooth Geomembrane /Soil Liner 21 0 <br />(Phase I) <br />Textured Geomembrane /Soil Liner 15 1,600 <br />(Phase II) <br />Textured Geomembrane / Geotextile 14 0 <br />(Phase II) <br />Foundation Material 40 0 <br />' I:\98\11a8\3148RRC.LTR Golder Associates <br />