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Mr. Peter Hays <br />TR -26 — TSF Liner System <br />April 29, 2015 <br />As the TSF `elevation increases with tailing deposition, the sand seam area will be inundated. With <br />Henderson's current deposition schedule, the lower portion of the seam will be inundated in late 2015, <br />once the impoundment reaches the 8875 -ft elevation. In order to minimize the risk for seepage of <br />process impacted water into the sand seam, Henderson plans to. construct a PVC geomembrane liner <br />system in the summer of 2015 (refer to Henderson Mill Sand Seam Mitigation Construction Drawings, <br />Sheets 1 -12, attached). <br />The liner system will be used to seal the potentially erodible zone of the sand seam, ensuring <br />containment of process impacted material within the TSF. A pre - welded PVC liner, covering 150,000 sq- <br />ft, will be installed in the project area. <br />The existing ground surface will be cleared of all vegetation and debris, then graded to a uniform slope' <br />from the 8870 -ft elevation to 8912 -ft. All exposed voids identified in areas to be filled and while <br />performing excavation activities will be completely excavated (three feet above and below) and backfilled <br />with compacted low permeability fill. The graded /filled base layer will consist of native material which is <br />free of lenses, pockets, streaks or layers of material differing substantially in texture, gradation and <br />moisture from the surrounding areas. It will also be mixed and blended such that a uniform mixture of <br />material is obtained to provide an obstruction -free foundation (i.e., rocks larger than 2 "). <br />Following the foundation preparation, a non -woven geotextile fabric will be placed flat and smooth on the <br />slope, free of tensile stresses, folds and wrinkles. The geotextile will overlap a minimum of 18 inches and <br />will be temporarily anchored by sand bags until the geomembrane is installed. Once the geotextile is <br />installed, the geomembrane will overlay it. <br />Installation of the geomembrane will occur on a day-by-day basis. More specifically, only the area of <br />membrane anticipated to be installed that day will be prepared for deployment. Additionally, only the <br />amount of top, side and toe anchor trenches anticipated to be ,completed in a day's time will be <br />excavated. The aforementioned is intended to limit the compromise that a weather event may create. <br />The geomembrane panels will be oriented parallel to the line of the slope (up and down the slope). <br />Where seams can only be oriented across the slope (side to side), the upper panel will overlap the lower <br />panel. Sandbags will be utilized for ballast material to prevent wind -based movement of the panels. The <br />exterior edges of the membrane will be anchored to the ground by means of a constructed trench, two <br />feet deep and two feet wide (see Anchor Trench Detail 2/6, 3/6 and 4/6, Sheet 12), then covered and <br />compacted with low permeability fill. <br />The seaming process will include trial seams and field seams. Trial seams will be routinely conducted <br />throughout the project and will be randomly tested for shear strength and peel adhesion to ensure <br />adequacy of the seaming equipment. Field seaming will then be conducted to' fuse adjacent panels. <br />Seams will consist of a 4 -6 inch lap, with a 0.5 — 2 inch seam, depending on the type of weld being <br />conducted. Non - destructive seam continuity testing will consist of Air Lance Testing Method (ASTM <br />D4437) and Air Pressure Testing (ASTM D5820) Standard Practice for Pressurized Air Channel <br />Evaluation of Dual Seamed Geomembranes. Additionally, destructive samples will be taken for every <br />500 linear feet of seam, at a location designated by the project engineer, and also at a location previously <br />undisclosed to the installer. Destructive tests will follow ASTM D6392 for Field Test of Peel and Shear. <br />The geomembrane will then be covered with random fill (select native material, tailing sand or a <br />combination of both). The geomembrane will be covered from the bottom up using six inch lifts, leaving a <br />cover no less than 12 inches, nominal depth. Additionally, no equipment will be permitted on top of the <br />liner system unless its operating on 12 inches of soil or more, puts less than 7psi to ground and the <br />equipment makes only smooth, non - abrupt turns. <br />The current TSF access road will also be relocated approximately 50 -ft to the north. Top anchor sections <br />of the liner which reside under the newly - aligned road will be protected by an additional layer of geotextile <br />over the geomembrane, which will be overlain by %" exterior -grade plywood and the nominal foot of <br />cover. An indicator (plastic orange safety fence) will also overlay the entire system to ensure that future <br />