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Easterly Wastewater Treatment Plant Expansion

City of Vacaville, CA

West Yost performed planning and design services for two major projects at the City of Vacaville’s Easterly Wastewater Treatment Plant (EWWTP), a $100 million Expansion/Upgrade Project and a $130 million Advanced Treatment Project.

Major facilities planned, designed, and constructed included a secondary process expansion, with the addition of nitrification and denitrification, construction of tertiary filters, a chlorine contact basin expansion, flow equalization facilities to eliminate blending, administrative/laboratory/O&M facilities, and the demolition and phase out of existing facilities.

The planning work was developed in two phases and culminated in the 2010 Master Plan, which is referred to as the Tertiary Treatment Project Facilities Plan. This planning document is built off of the City’s 1996 Master Plan, also developed by West Yost, that provided a forward-thinking, flexible approach that has stood the test of time from a regulatory and facility planning perspective.

Specifically, Vacaville was faced with a decision regarding if and how the old existing plant (North Plant) should be incorporated into an expanded plant.

West Yost conducted an extensive assessment of the existing structures, which included rigorous cost estimating, to determine the capital expenditures required to bring the old facilities up to comparable performance and reliability expectations of new facilities. This thorough analysis identified a strategy for maximizing the use of existing facilities without investing significant dollars, in order to minimize unnecessary expenditures as the older facilities were phased out/abandoned over a 10- to 15-year period. A new, readily-expandable South Treatment Plant was constructed to operate in parallel with the old (North) plant, with the expectation that the old plant would eventually be abandoned with capacity replaced in the South Plant.

The 2010 Master Plan identified a comprehensive program of improvements that phased out the North Plant facilities and upgraded the South Plant facilities to meet new regulatory requirements that mandated stringent ammonia and nitrate limits, eliminated blending, and enabled compliance with dry weather filtration/Title 22 reclamation standards. The evaluation of nutrient removal facilities included developing a calibrated BioWIN model of the treatment facilities to define the capacity requirements. The blending analysis identified and compared alternatives for eliminating blending, such as providing additional hydraulic treatment capacity to accommodate peak wet weather flow conditions, equalizing flows upstream of the hydraulically-limited systems to ensure capacity is not exceeded, or to provide some combination of equalization and treatment process expansion. The recommended combined strategy resulted in the lowest-cost approach for meeting the blending elimination goals.

West Yost recently designed an acetic acid storage and feed system at Vacaville’s wastewater treatment plant. The system is being used to promote more reliable denitrification at the wastewater treatment plant. This design effort required detailed research on storage and materials requirements for various acetic acid strengths, as our engineers discovered inconsistencies in the then-current engineering recommendations. West Yost is also currently providing engineering services for the design of odor control systems at the Vaca Valley Lift Station and Easterly Wastewater Treatment Plant.

West Yost won the CWEA Redwood Empire Section, 2007 Engineering Achievement Award for this project.

Team Spotlight

Thomas Hendrey, PE

Principal Engineer II

Kathryn Gies, PE, ENV SP

Regulatory and Planning Practice Area Leader, Engineering Manager II