2021-03-02_REVISION - M1990057 (5)

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1., The Ceadville Mill M 1990-057 EXHIBIT C—MILL PLAN Page 4-23 • Install leak collection sump and piping in pond corner and connect leak detection drainage net system to the sump. • Lining contractor to install geosynthetic clay liner, leak detection drainage net system and 45mil reinforced polypropylene. • Liner materials will be tested at intervals specified by manufacturer and contractor but not less than two tests will be performed. • Materials or construction not meeting standards and design specifications will be removed and repaired. 4.3.3 TSF STABILITY & TSF DESIGN (6.3.3(2)(b)) TSF stability and design activities described in this subsection were completed in 2014. The existing tailings facility will be removed and the new TSF embankment will be reconstructed as shown in Figure 4-3. The compacted fill embankment has a 2.5:1 (horizontal to vertical) outside face, and a 2:1 interior face. Fill material will have top size of 6in and contain approximately 50% silt and clay. Fill will be placed in 10-12in level lifts and compacted by a self-propelled sheep foot roller. Fill will be placed and compacted to 95% of Standard Proctor dry density (ASTM D 698). Fill will be scarified between lifts. Fill will be moisture conditioned to within 2%of 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 embankment as shown in Figure 4-3 and Figure 4-4. 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 are presented in the July 8, 2011 Report (see Appendix 15-5). Subsequently, CTL Thompson issued an update to the July 8, 2011 Report (see Appendix 15-6). 4.3.4 GEOCOMPOSITE DRAINAGE LAYER (6.3.3(2)(b)) The geocomposite drainage layer will be installed in the Spring of 2021.