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00Jacobs Associates is currently working with the owner, the Place County Water Agency, and the operator, Pacific Gas and Electric, to assess the possible degradation of the tunnel and surge shaft, and to investigate the possibility that leakage from the surge shaft has contributed to debris flows that have occurred in the adjacent hillside. The tunnel has not been inspected or dewatered since the last collapse occurred more than 25 years ago. Services have included providing a preliminary review of existing information, including as-built drawings, the inspection and repair reports from 1975, geotechnical documentation, and the Water Authority’s logistical and operational requirements and records; reviewing records of inspections conducted on both the shaft and portions of the tunnel using Remote Operated Vehicles (ROVs); assessing the potential for damage to the power-generating equipment based on studying samples of material passing through the tunnel and through the power turbines; and assessing repair alternatives for the surge shaft to limit the leakage out of the shaft and into the adjacent hillside.
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