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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />6.2 Outlet Works Rehabilitation <br /> <br />Repairs to the outlet works facilities have been determined to <br />be necessary to minimize the potential for seepage and infiltration <br />of embankment materials into and through the outlet. This is based <br />on the results of the field exploration program, including numerous <br />inspections of the outlet works and the 1986 dye flow test program. <br />Effective removal of the relatively short, high gradient seepage <br />path between the reservoi r and the insi de of the condui t shoul d <br />significantly reduce future sinkhole development in the vicinity of <br />the outlet works. <br /> <br />Rehabilitation of the outlet conduit is expected to entail the <br />following: <br /> <br />1. Construction of a coffer dam or equivalent water control <br />structure upstream from the intake structure to allow <br />temporary storage and diversion of in-basin flows while <br />work is performed. It is anticipated that the collected <br />water wi 11 be pumped over the embankmenti nto the Gurl ey <br />Canyon drainage at appropriate time intervals or piped <br />through the outlet tunnel after working hours; <br /> <br />2. Demolition of the existing intake structure including <br />removal of the existing trash rack, hydraulic cylinder, <br />hydraulic lines and manual control system, air vent pipe, <br />gate and concrete; <br /> <br />3. Excavation of a working area in the bedrock at the <br />upstream end of the outlet tunnel to facilitate <br />installation of the new tunnel liner; <br /> <br />4. Installation of a segmented welded steel plate liner <br />system in the 150-ft long upper tunnel and a 30-inch <br />diameter steel liner pipe in the lower tunnel, followed <br />by grouting of the space between the tunnel walls and <br /> <br />-21- <br />