Perris Dam Seismic Remediation and Seepage Recovery

Seismic Safety and Water Resource Resilience, California Department of Water Resources (DWR)

Located in Riverside County, approximately 60 miles east of Los Angeles, Perris Dam is a critical part of California’s State Water Project, serving as the terminal storage facility for the East Branch of the California Aqueduct. Since its construction in the early 1970s, the dam has provided essential water supply for recreation, wildlife habitat, and millions of Californians.

Lettis Consultants International (LCI) has played a key role in supporting the California Department of Water Resources’ (DWR) long-term efforts to ensure the seismic safety and hydrologic performance of Perris Dam, a critical water infrastructure facility in Southern California.

To address a potential liquefaction hazard in the dam’s foundation, DWR launched a major Seismic Remediation Project. LCI partnered with AECOM to provide full-time construction oversight during installation of cement deep-soil mixing (CDSM) cells, including 24-hour supervision of the ground improvement, validation coring, and real-time response to contractor RFIs. The project also included foundation excavation, replacement of upper foundation materials, expansion of the horizontal filter and drain zones, and installation of a downstream stability berm.

In support of the Seepage Recovery Project, LCI collaborated with other consulting firms to develop a detailed hydrologic model to assess the impacts of seepage recovery on the Perris North and South groundwater subbasins. This work supports DWR’s evaluation of dam safety under active seepage recovery and guides placement of new recovery wells.

Together with DWR and project partners, LCI helped enhance the long-term safety and resilience of Perris Dam—protecting vital water resources and infrastructure for the state of California.