Sonora Regional Wastewater Treatment Facility

PROJECT UPDATE – DECEMBER 1, 2021

Construction of the new Sonora Regional Wastewater Treatment Facility Project is in progress.  Kiewit Infrastructure West Co., the contractor hired for this project, is currently constructing two, 65-foot diameter, 18 foot deep, secondary clarifiers. The clarifiers incorporated in the design are part of the treatment process and are Secondary Clarifiers, meaning, they are located downstream of a biological treatment process. Once completed, wastewater will flow from two new aeration basins into the clarifiers.  From there, floating solids, such as oil and grease, float to the top and are skimmed off and removed, and settleable solids, more commonly known as sludge, settles to the bottom of the clarifier basin and is collected by a rotating rake system and removed.  Some of the sludge is conveyed back to the aeration basins where the cycle repeats.  The remaining sludge is thickened and conveyed to the aerobic digestion process where the sludge is processed and hauled offsite.  The clean effluent leaves the clarifiers for filtration and disinfection before entering the Quartz Reclamation System in Jamestown.

The photos above show the excavation of the slab and central footing of the clarifiers.  Once the slab is placed, will form and place the 1-inch-thick walls of the clarifiers. 

 PROJECT BACKGROUND

Tuolumne Utilities District is excited to announce that new construction is underway at the Sonora Regional Wastewater Treatment Facility.

Built in the 1970’s, the existing Sonora Regional Wastewater Treatment Facility (SRWWTF) is approaching 50 years of service and while it has undergone several process upgrades over the decades, the facility needs replacement. The District Board has awarded a construction contract to Kiewit Infrastructure West, Co., of Fairfield, Ca. in the amount of $35,025,010.

The Project started in October 2021 and includes constructing a new wastewater treatment facility capable of treating an average of 2 million gallons of wastewater per day that will meet the current California Title 22 Standards for Disinfected Tertiary Treated wastewater. Specific improvements include a new septage receiving facility, new headworks screening and grit removal system, secondary treatment process consisting of extended aeration, secondary clarification, tertiary filtration, disinfection, an emergency storage basin, rehabilitation, and conversion of existing secondary anaerobic digester vessels to aerobic digesters, new sludge screw press for solids dewatering, along with emergency standby power, and a new administrative/operations building. The project site is contained within the footprint of the existing treatment plant located at 1400 Southgate Drive in Sonora.

Most of the project cost will be covered thanks to a United States Department of Agriculture (USDA) grant/loan package that includes over $8.5 million in grant dollars, and approximately $24.9 million as a low-interest loan. TUD will contribute approximately $8.8 million of its own funds from wastewater reserves.

Project partners include Pacific Advanced Civil Engineering, Inc. (PACE), Kiewit Infrastructure West Co. (Kiewit), United States Department of Agriculture (USDA), Mountaineering Engineering, Condor Earth Technologies and Municipal Capital Markets.

Construction is scheduled to be completed within two years (2023).

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