Construction continues at EBMUD’s Orinda Water Treatment Plant on Camino Pablo between Manzanita Drive and Miner Road, where a major upgrade will improve water quality by adding ultraviolet disinfection.
Big things are happening at East Bay Municipal Utility District (EBMUD)’s Orinda Water Treatment Plant (WTP) on Camino Pablo Road, as an improvement project years in the making reaches a crucial stage.
Construction on the long-planned plant improvement project kicked off in July 2022. The work aims to update Orinda WTP’s basic filtration and disinfection process and reduce disinfection byproducts.
The Orinda WTP, built in 1935, is one of six EBMUD water treatment plants, and the public utility’s only plant that runs 24/7, year-round. The workhorse plant treats 50 million gallons of wastewater daily and delivers water to more than 800,000 customers every day.
Most of the water that makes its way through the Orinda WTP originates from snowmelt from the Pardee Reservoir at the base of the Sierra Nevada. The remaining 10% comes from the local Briones Reservoir.
All of that water must be treated and disinfected before it is distributed to the public, and one of the primary disinfectants is chlorine. Unfortunately, chlorine treatments produce byproducts that can be harmful, so an EBMUD goal is to lower the amount of chlorine used in the process.
Disinfection byproducts such as trihalomethanes (THMs) form when naturally-occurring organic matter comes into contact with chlorine. Increasing temperatures and other climate-related changes have increased the amount of organic material, which means more chlorine must
be used.
THMs show up in all chlorinated drinking water systems and are regulated to prevent risk to public health. The upgrade, which involves the use of ultraviolet light as a disinfectant, is designed to lower the amount of THMs in EBMUD water. (Note that the EBMUD drinking water supply met or surpassed every applicable state and federal requirement in 2025 even without the additional treatment.)
The new state-of-the-art ultraviolet (UV) water disinfection system and chlorine contact basin will create a multi-barrier disinfection process at the Orinda plant, one that EBMUD Senior Civil Engineer Tim Karlstrand calls “the gold standard in public health protection.”
The first set of UV reactors were scheduled to arrive the second week of July.
“It is exciting to finally receive the project’s first UV reactors from Germany after seven years of meticulous engineering and procurement,” said Karlstrand. “Seeing this sophisticated equipment arrive and be lowered into place will bring years of back-end design work into concrete, physical reality.”
The UV reactors, six in all, will be installed below ground, within the treatment plant’s UV reactor facility. A new, two-story maintenance building is also under construction, on top of that reactor facility.
The combination of UV disinfection followed by a chlorine contact basin means getting the most out of each method’s strengths and cutting back on chlorine use. The new system will also beef up EBMUD’s ability to remove bacteria and pathogens from the water supply.
The Orinda WTP’s backup power supply is also getting some necessary upgrades to bolster its resiliency in the event of power outages.
EBMUD projects that the new UV system should be online this coming winter, with construction all done by spring 2027.
EBMUD Public Information Representative Christopher Tritto confirmed that, looking further ahead, the public utility will be moving forward with more electrical, mechanical and architectural work on the plant’s maintenance building and disinfection facility.
Karlstrand called the Orinda WTP overhaul a career highlight, saying he feels honored to be entrusted to “lead the delivery of EBMUD’s largest and most complex civil engineering project in a generation.”
He acknowledged the work that has gone into the water treatment plant improvements.
“I am incredibly proud of our 100-plus dedicated project team members who pour their expertise and time into ensuring every single phase of the project is planned and executed in a safe and quality manner,” he said.
“A project of this scale relies entirely on the agency’s culture and the quality and dedication of its people.”
