2013-05-16_REVISION - M1990057 - Laserfiche WebLink

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optimum. Construction engineer will be on site to provide testing during fill placement and verify compaction of floor of pond by number of tests recommended by CTL Thompson. CTL/Thompson, Inc. has conducted slope stability analysis on the TSF embankments as shown in Exhibit TSF -02 and TSF -03. Samples were collected from drilling two (2) additional holes to verify and confirm the 1990 permeability test hole data and additionally confirm the embankment materials and underlying soils. Additionally, a sample of tailings materials generated from laboratory testing was analyzed. The embankment materials, native soils and tailings materials were tested for strength and classification, using direct shear tests for use in analyzing slope stability of the embankment. The results of the CTL Thompson Letter Report of July 8, 2011, are presented as Appendix A, Slope Stability Evaluation Tailings Pond Embankment and Future Tailing Slope, July 8, 2011. Subsequently, CTL Thompson issued an update to the July 8, 2011 Report, presented as Appendix B, Slope Stability Evaluation Tailings Pond Embankment and Future Tailing Slope, August 17, 2011. Phase 1 TSF reconstruction and Phase 2 new construction will use similar construction techniques and methods. The Phase 3 expansion lifts, will additionally use typical cyclone placement of select coarse material on the inside of the expansion embankments for increased stability. Geosynthetic Clay Liner A Bentomat° DN geosynthetic clay liner, or equivalent, is placed on the interior slopes and impoundment bottom. The geosynthetic clay liner is installed concurrent with the leak detection drainage net system and the 45 -mil polypropylene geomembrane liner. Geosynthetic clay liner specifications are presented in Figure C -4, Bentomat® DN. Leak Detection System Concurrent with the installation of the geosynthetic clay liner, a seepage /leak detection system is placed between the geosynthetic clay layer and the synthetic liner with the collection system located in the northwest corner of the impoundment, and the impoundment bottom sloping at ' /z% slope to the northwest. Exhibit TSF -05 shows additional details on the leak collection system and sump. The leak detection system is concurrently installed between the top layer of the 1 x 10 -6 cm/s (or less) geosynthetic clay liner and the 45 -mil polypropylene geomembrane liner. The leak detection system is a composite drainage product, produced by thermally laminating a 6oz/yd2 nonwoven geotextile to both sides of a polyethylene drainage net, capable of intercepting liquid within the leak detection zone and conveying the liquid to a collection sump for storage. The leak detection drainage net system is shown on Exhibit TSF -05 and Exhibit TSF -06. The volume of the collection system is limited to the sump and is approximately 90 gallons. The sump is accessed through a 4in PVC pipe to the top of the impoundment. Collected leachate will be returned to the TSF and then recycled to the mill through the impoundment decant pump(s). The leak detection system requires a manual inspection of the sump through the 4in PVC pipe. If leachate is detected (indicating a leak in the 45 -mil polypropylene), the level will be monitored, a small pump will be installed in the PVC pipe and the Division notified of fluids from the leak detection system. If groundwater is detected (indicating a leak in the geosynthetic clay liner), the level will be monitored, a small pump will be installed in the PVC pipe, the groundwater pumped to the impoundment and the Division notified of fluids from the leak detection system. Leak detection drainage net system specifications are presented in Figure C -5, TexDrain® TD 300. M1990 -057 May 14, 2013