2011-03-14_REVISION - M1977493 (62)

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t` F x3 ?f r C P C • r: r Uk L CM0001636 Page 8 a hydraulic barrier to isolate the Eagle Park Reservoir from being adversely impacted by the seepage of poor quality water emanating from Robinson Lake and No. I Tailing Dam. The drain will act as both a collection drain/pump-back system by collecting ground water downgradient of Robinson Lake and pumping the ground water back into the lake. The Robinson Lake drain will consist of perforated pipe(s) or similar drainage system connected to a collection sump. The drainage system will be placed in an excavated trench and backfilled with a pervious material, such as gravel. A 10 to 50 gallon-per-minute-rated submersible pump placed within the collection sump will be used to pump the collected ground water from the drain to Robinson Lake. A generalized schematic of the drain system is shown in the cross section on Figure 5 and in the plan on Figure 3. General design specifications for the drain are presented in Appendix A. Optionally, a cutoff wall (such as a slurry wall or geosynthetic wall) could be added to the drain. The purpose of the cutoff wall will be to enhance the performance of the drain by focusing the collection of ground water upgradient of the drain. In addition, the cutoff wall will provide a physical barrier to flow, thus adding a factor of safety to the protection of the Eagle Park Reservoir. Operation of the Robinson Lake drain will not violate Section 404 of the Clean Water Act. Section 404 deals mainly with discharges to wetlands. The water collected by the drain will be discharged back into Robinson Lake and not into the surrounding wetlands. In addition, operation of the drain will not dewater the area, thus disturbing the wetlands. Therefore, wetland disturbance, if any, would be minimal. 3.13 Robinson Lake The goal of reclaiming Robinson Lake is to improve the water quality in the lake for ultimate discharge to downstream users. Two reclamation measures were evaluated for Robinson Lake: • Active reclamation, and • Passive reclamation. The following sections provide a summary of the applicable reclamation measures for Robinson Lake. Active Reclamation Active reclamation of Robinson Lake will be similar to the approach used for the Eagle Park Reservoir. Activities associated with active reclamation are illustrated on Figure 3 and include: Elimination of poor quality surface water discharges to Robinson Lake from the