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SFPUC says Calaveras Dam construction progressing but geologic findings raise cost and schedule risks
Summary
The Water System Improvement Program is largely on schedule, but new geologic jointing discovered in a borrow area for the Calaveras Dam replacement will require additional excavation support, rock bolts and shotcrete, adding cost and schedule risk; staff will bring mitigation options at the December quarterly report.
At Friday’s San Francisco Public Utilities Commission meeting staff said the Calaveras Dam Replacement Project is more than 70% complete in construction but faces new geologic challenges that could increase costs and require schedule mitigation.
Dan Wade, Water System Improvement Program director, told commissioners that crews have initiated mining in the Bar Area B hard‑rock quarry and completed 14 of 16 borings. Tests showed pervasive jointing in the rock that is locally interconnected and in places out‑of‑slope, which will require additional excavation support — specifically more rock bolts and additional shotcrete — than previously planned.
"This means additional rock bolts and additional shotcrete to support that slope as they continue to excavate down," Wade said, adding that staff are evaluating acceleration of critical activities and other mitigation measures and that he will present options at the December quarterly report.
Wade also reported progress: foundation excavation is nearly complete for the portion that can be excavated before the conduit installation; more than 40,000 cubic yards of concrete have been placed on the new spillway; and the project has started hard‑rock mining activities. He cautioned, however, that the increased excavation support will add cost and create scheduling challenges.
On the broader Water System Improvement Program (WSIP), Wade said the regional program is roughly 90% complete and the local program nearly 100% complete, with the overall program on track for an approved completion date of May 19, 2019. He noted unresolved claim negotiations and the potential for erosion of the director's reserve for several projects (Harry Tracy Water Treatment Plant, New Riverton Tunnel, and Calaveras trends).
Commissioners asked for cost and schedule forecasts; Wade said he expects to have a mitigation forecast for the December quarterly report. No formal action was taken on the Calaveras issues at the meeting.
