B.F. Sisk Dam Seismic Retrofit and Reservoir Expansion

B.F. Sisk Dam holds back San Luis Reservoir, and it sits close enough to the Ortigalita Fault that Reclamation has spent the better part of a decade deciding how much of it to rebuild. The answer turned out to be most of it. At 382 feet tall and three and a half miles long, Sisk is the largest structure the Bureau has ever taken on under the 1978 Safety of Dams Act, and the current program estimate runs to roughly $1.1 billion.

The work is phased. Phase 1, awarded to NW Construction at $119.97 million, built stability berms and prepared the foundation between 2022 and 2024. In May 2025 Reclamation awarded the same contractor a $255 million Phase 2 package for a large central stability berm that calls for something on the order of 15 million cubic yards of earthen fill. The final phase raises the crest 10 feet for dam safety alone.

Project Scope

Seismic stabilization of an existing 382-foot earthfill embankment sited near an active fault, delivered in three phases inside an operating reservoir. Phase 2 alone moves roughly 15 million cubic yards of fill. A 10-foot crest raise addresses the dam safety deficiency. A second 10-foot raise, negotiated separately between Reclamation and the San Luis & Delta-Mendota Water Authority, adds about 130,000 acre-feet of storage on top of the safety work. Geocomp handles geotechnical instrumentation and monitoring; the Hallmark Group manages the raise program.

Why It Matters

Two things are stacked here that usually get built separately. The seismic fix is federal dam-safety money and would have happened regardless. The storage expansion is a water-supply project that rides on the same earthwork, which is the only reason a 130,000 acre-foot increment pencils at all — the mobilization, the borrow sources and the crest work are already paid for. That structure, a local water authority buying incremental capacity on top of a federal safety retrofit, is worth watching as more of the West’s aging embankment dams come up for the same treatment. There aren’t many places left to build new reservoirs. There are a lot of existing dams that need to be rebuilt anyway.

Project Team & Details