Laguna plant UV upgrade nearing later-than-expected finish; $55M spent to date

Santa Rosa Water on Tuesday briefed the City Council on progress at the Laguna Treatment Plant, where a major upgrade to the plant’s ultraviolet (UV) disinfection system has been under construction since 2022.

Deputy Director Mike Prins said the project has included deep excavation, sheet-piling, a 42-inch high-density polyethylene diversion pipeline and five UV treatment channels. To date, Prins said, the city has spent nearly $55 million on construction, including about $3.2 million in change orders, and that the contractor has logged roughly 75,000 labor hours.

Prins said the new facility will restore the plant’s full previous recycled-water treatment capacity — about 70 million gallons per day — after regulatory derating reduced the old system’s output. He said the upgraded system is expected to be more energy efficient, saving in the order of $400,000 a year in electricity costs compared with the older system. Prins also noted that much of the recycled water treated at Laguna serves local beneficial uses, including geothermal operations at The Geysers and agricultural customers.

Construction photos in the presentation showed large concrete pours (walls up to 23 feet high and 3 feet thick), nearly 40,000 cubic yards of excavation and a massive installation of rebar. Prins described a diversion pipeline installation using fused HDPE pipe sections and showed drone photos of trenching through the plant’s main parking area. He said the system will incorporate 25 UV banks; Prins noted one bank contains 104 bulbs, for a total of about 2,600 bulbs across the facility’s channels.

Prins said Shimek Construction is the prime contractor. He told the council that the contractor’s burn rate is high — roughly six figures per business day — and that the project has used a significant portion of its contingency. Prins said the team previously estimated a July completion but now expects construction to continue beyond July 2025.

Council members asked about benefits to the community and how the plant supports regional recycled-water use. Prins reiterated that restoring and improving capacity is essential because Santa Rosa typically recycles nearly all of the water it produces at Laguna and that the plant serves about 240,000 customers in the region. He said Santa Rosa accounts for roughly 73% of the flow to the Laguna facility; other customers include nearby cities and unincorporated county areas.

Prins said the replacement is intended to make operations more reliable, to restore capacity lost through regulatory derating, and to reduce annual electric costs. No formal council action was taken on the project during the briefing.