“This is a significant milestone for COWI in Southern California,” Arun Parsons, vice president of COWI North America, said in announcing the contract on Sept. 30.  GFT is the entity rebranded earlier this year that was formed by the combination of Gannett Fleming Inc., TranSystem Corp. and other firms.

Expansion Scope and Oversight

The district's environmental filings, reviewed by ENR, call for demolishing the current dam and building a 136-ft embankment, raising the crest from 388 ft to 466 ft above mean sea level. 

Planned improvements include a new spillway, seepage drainage system, upgraded outlet and circulation works, and filtration and disinfection facilities at the dam toe. New access and maintenance roads will be built, along with wetland and riparian mitigation areas.

A schematic map shows the planned Syphon Reservoir Improvement Project in Irvine, Calif., including the footprint of the new 136-ft dam, proposed treatment facilities, spillway, intake and outlet works, and inundation area. Image courtesy of Irvine Ranch Water District/EIR.

To reinforce public confidence, the district convened an independent design and safety review panel in 2021 of nationally recognized dam engineers. They conducted staged design reviews and site visits, issuing a closure letter in February that confirmed concerns had been resolved and met California Division of Safety of Dams requirements.

Construction is expected to last two to three years. The district has not yet awarded a prime contractor, although permitting and the design by AECOM are complete. ESA is the environmental consultant managing CEQA compliance.

To reduce community impacts, the district plans to restrict truck access during peak hours, limit most activities to weekdays and enforce dust and noise controls.

Financing and Long-Term Value

Funded through an existing capital facilities assessment already collected on property tax bills, the $291-million program will not raise drinking water rates, the district says.

Federal support includes a $12.25-million award under the Bipartisan Infrastructure Law WaterSMART program. At the funding announcement, then-Interior Secretary Deb Haaland said the Syphon Reservoir expansion “underscores the federal commitment to strengthening drought resilience in California.”

The district projects long-term customer savings by reducing its purchases of imported water from Northern California and the Colorado River. “[T]he Syphon Reservoir Improvement Project is expected to save customers approximately $85 million over 50 years,” the district stated.

Because the expanded reservoir will allow storage and reuse of nearly 100% of recycled water produced, the increased supply could be deployed in summer months for irrigation, industrial cooling, dust control and fire suppression, enhancing long term water reliability, the district noted. 

The district's recycled water network spans 570 miles of “purple pipe”—the industry-standard color used to distinguish non-potable water lines—and serves more than 6,200 water accounts, or 28% of total deliveries.

COWI has worked on other California reservoir and dam projects, including Anderson Dam, Lafayette and Briones Reservoirs, Chabot Dam and Folsom Dam.