A proposed Tuolumne River treatment plant could add about $25 to average monthly water bills in Turlock and Ceres.
That is the latest estimate for the project, which would supplement city wells that can be hampered by drought and water-quality rules.
The governing board voted unanimously last week to do further planning on the $288 million project. It could be completed as early as 2022.
The rate analysis was done by West Yost Associates, a Davis-based engineering firm. It assumes that bills will rise anyway because of the need to maintain the groundwater systems, and that the treatment plant would add further to the costs.
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The average Turlock bill of $43 a month would rise to $52 by 2022 with a groundwater-only system and to $77 if it added the river water.
In Ceres, the average monthly bill of $42 would be $51 in 2022 with a groundwater-only supply and $78 with the river water.
West Yost notes that customers could pay less if the project qualifies for state or federal grants.
The project, discussed off and on for about 30 years, is finally getting traction. The Turlock Irrigation District agreed in 2015 to sell some of its river water to the plant. It would use an intake structure that TID installed in the riverbed at Geer Road in anticipation of the project in 2001.
The effort in the past involved several smaller towns within TID boundaries, including Hughson, Keyes, Denair, Hilmar and Delhi. They can rejoin by covering some of the costs, said Michael Brinton, interim general manager for the project.
The Modesto Irrigation District built its own treatment plant in the mid-1990s for domestic water users north of the Tuolumne. It is credited with helping groundwater bounce back.
The proposed plant’s governing body is formally known as the Stanislaus Regional Water Authority. It is made up of Mayor Gary Soiseth and Councilwoman Amy Bublak from Turlock and Mayor Chris Vierra and Councilman Ken Lane from Ceres.
The board hired the engineering firm last year on a $2 million contract for early planning. It added $273,255 last week for further tasks, but the detail design will be substantially more.
John Holland: 209-578-2385