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hydrostatic head on the geomembrane liner will be less than two feet. UMC will continuously <br />decant the water for reuse in the mill to minimize makeup water requirements. Typically, <br />tailings will be laid down in a bench, or splay within the impoundment and a barge mounted <br />decant sump pump(s) located at the lowest level will pump the water back to the mill. This <br />pump(s) will be pressure sensor activated (or float switch activated). <br />UMC is incorporating a standard liner keying system. Typically this is a trench 1.5ft wide, <br />approximately 2 feet or more from edge of the inside slope, 2 feet deep. The liner is rolled down <br />the trench wall, across the trench floor, and then the trench is backfilled and compacted to the <br />specified embankment compaction standards. <br />Geomembrane liner specifications are presented in Figure C4, 45 mil Polypropylene Liner, <br />Geotextile Liner <br />UMC has committed to the Division to initiate removal of the existing onsite ore stockpiles <br />within 60days following startup. The overliner material is currently stockpiled on the west side <br />of the mill entrance road, at the "Y" for the lower access (south) road. This material is angular <br />and of varying size, but predominately -1 in with a large fine proportion. <br />The impoundment liner will be held in place with material from the ore stockpiles discussed in <br />the ORE STOCKPILES section. The material may be directly placed as an approximate 12 -inch <br />overliner to hold and protect the Polypropylene Geomembrane liner, or placed in sand bags and <br />placed on the liner. Additionally, the existing on -site stockpiles may also be initial feed stock for <br />mill startup with the tailings reporting to the tailings facility. These stockpiles are on -site and <br />have been covered with visqueen since 2009. <br />UMC is placing a 12oz non -woven geotextile liner over the polypropylene liner on the bottom of <br />the impoundment to protect the liner from puncture. The impoundment bottom is approximately <br />16,000sf. A service ramp (at 2:1 slope) will be built from the top of the embankment to the <br />bottom of the impoundment and the geotextile liner will also be placed under this ramp. The <br />bottom of the impoundment will have a l ft deep overliner placed on the geotextile liner. The <br />ramp will have a 1.5ft deep layer of overliner material. Only low ground pressure equipment <br />will be allowed on the access ramp. This material will remain in the pond following startup of <br />the facility. Approximately 875st of material will be used in the overliner. This overliner is to <br />prevent "lift" of the liner material in high winds and provide a service layer to access the pond <br />without puncturing the liner during the start up phase of the mill. <br />The slopes of the impoundment will not receive direct placement of overliner material. Ballast <br />tubes from the top of the embankment to the bottom of the impoundment, typically constructed <br />from 6in PVC tubes or geotextile socks and filled with the same overliner material, will hold the <br />liner down following installation until the tailings cover the exposed liner. These ballast tubes <br />will be held in place from the top by keying into the anchor trench and extend 1 ft onto the <br />overliner on the impoundment bottom. The ballast tubes will not prevent lift, but will minimize <br />lift <br />M1990 -057 September 27, 2011 <br />