2021-03-02_REVISION - M1990057 (5)

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The Lead,,lle Mill M 1990-057 EXHIBIT C—MILL PLAN Page 4-28 SUBBASE CONSTRUCTION, G D L AND G C L A\'n GEOSY ITHETIG CLAY LINER INSTAL I ATIA\I • Finished surface shall be firm and unyielding, without abrupt elevation changes, voids, cracks, ice or standing water. • The subbase will be constructed during a period of low flow to ensure that the GDL will protect the GCL from premature hydration. • Liner contractor will install and test the geocomposite drainage layer in accordance with manufacturer's recommendations. Installation of the GDL protecting the GCL from premature hydration is shown in Figure 4-7. 19 • Liner material contractor will inspect the subbase prior to commencing installation. • Liner material contractor will install and test the geosynthetic clay liner in accordance with manufacture's recommendations. • The liner material contractor will inspect a known perched aquifer seep approximately 4ft above the bottom of the TSF floor and employ one of the techniques below, or equivalent,to minimize premature hydration when laying the geosynthetic clay liner over the seep area. o No special procedures: ■ Seep has minimal flow (damp, dry) or the seep flow is controllable with standard pumping techniques (minimizing standing water) and no additional liner installation techniques required. o Visqueen liner below seep: ■ Seep flow is controllable with standard pumping techniques (minimizing standing water), but flow from the seep may cause hydration of the geosynthetic clay liner below the seep faster than desired. ■ Visqueen or equivalent liner placed from the seep to the TSF floor, reducing hydration of the GCL material and directing seep flow to the TSF floor for control by standard pumping techniques. 19 A1AR1Q5