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The Bentomat DN product was specifically selected as the necessary - GCL for its higher shear strength resistance. <br />The natural slope, upon which the liner and tailings will reside, is slightly less than 3h: Iv (± ig = 18°). Because of <br />this, it was important to analyze the interface friction capabilities of this component versus the sub-grade. <br />TRI/Environmental tested this utilizing a representative sample of sub-grade soil prepared as described in the GCL <br />installation specifications. The all of the interface friction testing (ASTM D-6243) was carried out using normal <br />stress values of 1000, 7500, and 15000 lb/fe which represents static loading upto a maximum tailings depth of 88 ft. <br />(loading conditions were taken asstuning a depth of 88 feet of deposited tailings, averaging 11 I lb/fO density, plus a <br />1.53 safety factor -a confining pressure approximated at I5,000 lb/fe). TRI reports an interface friction angle, cp = <br />23.6°, which corresponds to a slope of 2.3h:1 v. The sub-grade slope is less than this and provides for a factor of <br />safety, FS = tan cp/tan ig = 1.3 (USACE Slope Stability). See TRI's complete findings in the appendix of this Exhibit <br />C. <br />An impervious Geomembrane liner shall be installed on top of the GCL. A 60 mil HDPE product was selected for <br />its durability and chemical/UV resistance. This is also supplied textured which provides for "gripping" strength <br />when installed in inclined positions. The textured surface grabs hold of the geosynthetic fabric of the GCL below <br />and the GeoComposite to be installed above it. Installation and QA/QC procedures shall conform to manufacturer's <br />specifications contained in the Composite Liner Submittal included within the appendix. The Geomembrane shall <br />be attached to the concrete footing of the concrete leachate collection barrier following the installation specifications <br />"Sealing Membrane to Concrete with Batten Bar" contained in the Composite Liner Submittal. <br />TRI performed a Geomembrane interface friction test using the normal stress values described earlier. For the <br />Bentomat DN versus the textured 60 mil HDPE Geomembrane, TRI reports an interface friction angle, T = 26.6° <br />which corresponds to a slope of 2h: Iv. The sub-grade slope is less than this and provides for a factor of safety, FS = <br />tan (p/tan ig = 1.5 (USAGE Slope Stability). See TRI's complete findings in the appendix of this Exhibit C. <br />On top of the Geomembrane, a drainage/filter layer shall be installed. This GeoComposite layer consists of a geonet <br />sandwiched between layers of 6 oz. geotextile, with the assembly being fused together. This GeoComposite allows <br />for filtering and draining leachate from the impounded tailings (it will also serve as a protective layer over the <br />HDPE liner). This will greatly facilitate more rapid de-watering and consolidation of the tailings. More <br />importantly, the GeoComposite acts as a continuous underdrain that will greatly diminish the hydrostatic head acting <br />on the .EIDPE liner to less than three feet. Leachate will drain down the top of the HDPE liner and be collected at the <br />concrete leachate collection barrier leachate recycle sump. The leachate will then be pumped back to the Millsite <br />Water Holding Pond for reuse. <br />To further ensure complete dewatering, a system of 4" perforated pipe with a geotextile filter sock shall be installed <br />into the Tailings Impoundment as a more active drainage element. This is above and beyond the more passive <br />drainage achieved by the Geocomposite filtering liner layer specified above. This network of 4" French Drains <br />(perforated plastic pipe with an integral filter sock) shall be installed on top of the Geocomposite layer in the middle <br />1/3 zone of the Tailings Impoundment. This is the deepest zone and most likely to be saturated. These drains shall <br />be laterally spaced at a maximum of 10' and run down the slope to collect at the leachate collection sump located <br />within the Concrete Leachate Collection facility. The drains will be extended as the impoundment is built upwards. <br />Having the upper end of the drain exposed will allow the ability to purge the lines if they become plugged. <br />TRI tested the GeoComposite for drainage and resistance to plugging. TRI conducted a Hydraulic Conductivity <br />Ratio (HCR) test comparing performance of the GeoComposite with the coarse and slimes fraction samples. The <br />HCR test reports the diminished drainage, "plugging", of the GeoComposite as a ratio relating to the soil drainage <br />properties. <br />In summary, the HCR test results for the GeoComposite vs. coarse fraction reports a ratio of HCRCO?r,e = 0.52 and a <br />hydraulic conductivity of the coarse fraction affected GeoComposite kGeo v. eoe = 32 x 10-6 cm/sec. Similarly, the <br />HCR test results for the GeoComposite vs. slimes fraction reports a ratio of HCRSrimeS = 0.77 and a hydraulic <br />conductivity of the slimes fraction affected GeoComposite kGeo slime, = 2.3 x 10-6 em/sec. Even though results were <br />reported for both coarse and slimes fraction, it is almost certain that the majority of the GeoComposite will see <br />interface with the slimes fraction. See TRI's complete findings in the appendix of this Exhibit C. <br />Page 28 of 37