Sonoma Water outlines multi‑year transmission upgrades, tank rehabilitation and pilot aquifer recharge plans

Sonoma Water staff briefed the Cotati City Council on a multi‑year program of infrastructure work that will affect regional water supply and reliability.

The presentation, led by Kent Gilphy, director of engineering for Sonoma Water, summarized projects now in construction and design, including a 10‑year tank rehabilitation program, cathodic protection upgrades on aging aqueducts, several booster pump station upgrades, and a pilot program to enable two production wells in the Santa Rosa Plain for aquifer storage and recovery (ASR).

The agency said the tank rehabilitation program is among its largest single investments: an approximately $80 million, 10‑year effort to recoat and upgrade 18 storage tanks totaling about 128 million gallons of storage. ‘‘We recently completed the Cotati 1 tank, and we just awarded the contract for Cotati 3, which is an 18 million‑gallon tank that will be out of service for much of 2025,’’ Gilphy said.

Why it matters: Sonoma Water is the wholesale supplier for many local retail agencies, including Cotati. The transmission projects and reliability upgrades are supported by rates that affect Cotati customers and, the agency said, are intended to reduce the risk of outages during earthquakes, floods and other hazards.

Key projects and schedule details - Wells and ASR: Gilphy said Sonoma Water rehabilitated three production wells in the Santa Rosa Plain and obtained a $6,900,000 drought‑resiliency grant to upgrade two additional wells for both production and future aquifer recharge. The agency expects one ASR permitting milestone by the end of 2025 and additional pilot testing in 2026.

- Tank program: The rehabilitation program will address interior/exterior coatings, cathodic protection and seismic vulnerabilities. The Cotati 3 tank project will include widening the foundation ring to address an eccentric load condition, Gilphy said.

- Cathodic protection and aqueducts: Sonoma Water is converting passive cathodic protection systems to impressed current systems on several aqueducts; parts of that effort will proceed to construction in 2026, the agency said.

- Treatment modernization: A multi‑phase project was described to replace aging chlorine gas systems with hypochlorite treatment and to address electrical, flood and seismic vulnerabilities at river facilities, Wohler and Mirabel pumping sites, and at River Road.

Operational context and constraints Gilphy noted ongoing supply‑chain challenges for electrical gear that have delayed some projects and pointed to coordination needs with other agencies for certain tasks. The agency also described a master plan process, scheduled for completion in fiscal 2026–27, that will help prioritize projects and update long‑range financial planning.

Sanitary survey and compliance Gilphy told the council Sonoma Water recently completed a two‑day sanitary survey by the state Department of Drinking Water with no significant deficiencies in pumps, system management or operator compliance; only minor findings remain to be addressed.

What council members asked Council members asked about ASR timing and coordination with PG&E for cathodic protection work. Gilphy said the agency expects permitting for one ASR well by the end of 2025 and pilot testing in 2026, and that PG&E coordination had not been a critical path item so far but remains a scheduling concern on some sites.

Ending Council members thanked Sonoma Water for the briefing and accepted the invitation to tour the agency’s river facilities.

Speakers quoted or referenced in this article Kent Gilphy, Director of Engineering, Sonoma Water; David Royal, Assistant General Manager, Sonoma Water.