The Main West Tank Project effectively addresses challenges to deliver an award-winning project for the City of Paso Robles.

Having deferred the replacement of an existing 97-year-old earthen water reservoir, the City of Paso Robles turned to WSC address facility reliability, improve water system hydraulics, and enhance the seismic safety of the water distribution system. WSC served as project manager for the delivery of a new, partially buried water storage tank to support the City’s goal of reducing seismic risk on the water distribution system and enhancing system safety and performance. WSC’s evaluation of rehabilitation or replacement options concluded a new 4 million gallon (MG) partially buried pre-stressed concrete tank on the existing reservoir site provided the greatest value for long-term costs and performance.

The new structure is a partially buried, strand-wound, circular, prestressed concrete water tank per American Water Works Association Standard D110. Because this tank type can be partially buried, it would fit within the physical site constraints and work with the existing system hydraulics. And because the project site required that the existing reservoir be taken offline and demolished prior to the construction of the new tank, the City was without 4 MG of stored water for approximately two years. Significant analysis was done pre-construction to confirm the water system’s ability to handle lost water storage, meet fire flows, and optimize the operation of pumps during construction. To temporarily replace the loss of surge relief that the existing tank provided, the City installed a large stand-pipe that extended above the hydraulic grade line of the water system.

Successful delivery of the community’s new water storage tank included addressing facility, site, and COVID-19 pandemic challenges, including:

• Community impacts: The highly visible tank is on a hill above downtown Pas Robles. Partially burying the tank minimized the site’s visual impact and landscaping was selected and positioned to provide additional site screening. The above ground exterior concrete was stained to reduce visual impacts and to help the structure blend into the hillside.
• Emergency overflow: Providing thoughtful site drainage design to properly address emergency tank overflow scenario, reduce attenuated runoff, and minimize offsite flow.
• Cost control: Reaching out to specialty tank contractors during the early design phases allowed the design team to fully understand the expected costs and supported informed design decisions. High-cost items were eliminated from the design, including products from proprietary suppliers that were overpriced due to limited competition. The resulting selected bid was within 1% of WSC’s engineer’s estimate.
• Continued value through the end: Upon final inspection and prior to commissioning the tank, WSC addressed DDW’s concerns of perceived elevated pH levels due to concrete dust (prior to filling tank) by developing and implementing a testing plan to mitigate concerns and meet the schedule for operations.
• Quality contract documents: The City and WSC worked together to address quality issues from pipeline manufacturer and installation subcontractors. WSC advocated for the City and advanced an alternative that better met the City’s needs and desired level of quality.

In 2022, the American Society of Civil Engineers (ASCE) Central Coast Chapter recognized the Main West Tank Project with their Outstanding Water Project award. The Main West Tank project was also selected for ASCE’s Los Angeles Section Project of the Year. The new water distribution facilities provide the City and its residents with improved water system performance and reliability—creating a better water future ^®.