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• Composite Liner System: <br />The DRMS has determined that practice based ground water protection be applied to this operation through the <br />implementation of a composite linersystem under the Tailings Impoundment. <br />Venture Resources has sought the expertise of Colorado Lining International in specifying the necessary <br />geosynthetic products suitable for this application. A three component system is specified consisting of a <br />Geosynthetic Clay Liner (Bentomat DN), overlain with a textured 60 mil HDPE Geomembrane impervious liner, <br />overlain with a GeoComposite drainage layer. Specification sheets have been included as an appendix to this <br />Exhibit C. <br />The Geosynthetic Clay Liner (GCL) shall be placed directly on the base grade as the first layer. The GCL provides <br />for a secondary, self-healing liner that will contain any slight seepage that may occur through the Geomembrane. <br />The GCL also allows for a cushion between the base grade and the Geomembrane, mitigating chances of a rough <br />surface from puncturing through to the Geomembrane. This liner is composed of a geosynthetic fabric "pillow" <br />with bentonite clay sandwiched between. In the event moisture permeates, the bentonite clay will swell to seal. <br />Refer to the Composite Liner Submittal in the appendix for specifications pertaining to sub-grade preparation and <br />installation utilizing an anchor trench method. <br />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:1 v (f 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/ft2 which represents static loading upto a maximum tailings depth of 88 ft. <br />(loading conditions were taken assuming a depth of 88 feet of deposited tailings, averaging 111 Ib/ft3 density, plus a <br />1.53 safety factor - a confining pressure approximated at 15,000 lb/ft2). 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 q/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, cp = 26.6° <br />which corresponds to a slope of 2h:1 v. The sub-grade slope is less than this and provides for a factor of safety, FS = <br />tan y/tan ig = 1.5 (USACE 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 HDPE 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 />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 />Page 26 of 35