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~• 3.1 GENERAL 3.0 SLURRY WALL CUTOFF AND PUMP-BACK SYSTEM 3-1 The primary objective of the slurry wall cutoff and pump-back system vas to (a) intercept tailings pond seepage in downstream areas by providing a barrier to surface and subsurface floe, (b) collect Lntercepted eater, and (c) return, by pumping, collected water to the tailings pond. The locations, components, and details of the system ate presented in Figures 2 and 3. Components of the slurry wall and pump-back system include: 1 l o A bentonite/soil slurry wall and embankment downstream of the toe of the dam to provide a barrier to seeping tailings eater, and to contain runoff from precipita- tion in uncontrolled upstream areas. o A collection system upstream of the slurry wall to channel all seepage to a collection trench connected to a concrete sump. o A concrete sump and pump-back system consisting of two turbine pumps which return the tailings eater back to the pond. o A nee buried discharge line that connects the pump- back system to the tailings pond. Construction of the slurry wall cutoff and pump-back system began on July 8, 1982. Preparation first began for the cross-valley embankment to serve as a working grade for slurry wall excavation as yell as a retention embankment for surface floe. Auger drilling from the top of the completed embankment was conducted from July 11 to July 13, 1982, to delineate the depth to competent rock along the slurry wall axis. Construction of the slurry wall itself, including excavation, soil/bentonite mixing, backfilling, and protective cap placement began on July 14, 1982, and vas completed on July 17, 1982. Construction of the drainage collection trench occurred from July 22, 1982, through July 27, 1982. Construction proceeded with final fill placement around the sump along with the pouring of the concrete slab on July 30, 1982. Complete hook-up of the pumps and pump-back system occurred on August