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Zone 7's Patterson Pass plant shifts to ozonation water treatment process

Original post made on Jun 22, 2022

Residents in the Tri-Valley region will start to see and taste a difference in their tap water thanks to upgrades the Zone 7 Water Agency has made to the Patterson Pass Water Treatment Plant in Livermore.

Read the full story here Web Link posted Tuesday, June 14, 2022, 7:06 AM

Comments (2)

Posted by Ko
a resident of West of Foothill
on Jun 22, 2022 at 8:21 am

Ko is a registered user.

Good to know. Hopefully this will help get Pleasanton water quality up past "bad" when algae is going wild. What aging equipment was replaced? Presumably better filtering but that was unclear.

Posted by keeknlinda
a resident of Vintage Hills
on Jun 22, 2022 at 2:30 pm

keeknlinda is a registered user.

At the ribbon-cutting, which I attended, it was made clearly known that the Patterson Pass facility has come online after the Del Valle treatment plant switch to zonation was completed in early 2021. Much of the Tri-Valley service area already has been receiving ozone-treated water from that plant. Zone 7 has operated the two plants for some years, and location within that service area determines which plant's water your home gets.
Pleasanton was changed over in 2021 and there was a change that improved the algae issue more than a year ago. Many people noticed it, others did not and continued complaining about the water. Some portions of Livermore didn't get that better-tasting advantage until Patteron Pass came online.
Because Pleasanton is supplied from both surface water through the Delta and groundwater, the origination of the supply is blended, 70-80% surface, the remainder groundwater. Because the drought has reduced the amount of surface water available through the State Water Project over the past couple of years, a greater ratio of groundwater is being used. And groundwater is inherently hard water.
Regarding what equipment was replaced, the whole plant was torn down and a new one built, so all equipment is new, and rather than the previous chlorination method, ozonation is now being used. Del Valle plant was modified, but Patterson Pass was simply replaced.
One of the biggest advantages of ozone treatment is how effective it is at treating that periodic algae issue that sometimes occurs in summer. Taste and odor are most effectively treated with ozone, thus allowing more consistently good-tasting water coming from your tap.
For more information, visit and you can read about the entire treatment operation.

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