Mesa completes new reservoir as part of $168M Signal Butte plant expansion
Construction on the City of Mesa’s $168 million expansion of the Signal Butte Water Treatment Plant has reached a major milestone with completion of a new 8-million-gallon potable water reservoir. McCarthy Building Companies Inc. is serving as general contractor, with Black & Veatch as engineer of record on the multi-phase project.
The expansion is being delivered in two phases on the 84-acre site north of Elliot Road and east of Signal Butte Road, allowing the existing treatment plant to remain fully operational throughout construction. Phase I began in January 2024 and is scheduled for completion in October 2026. It includes the new reservoir, a second reservoir, system redundancies to improve reliability, and infrastructure to support the future Phase II expansion.
The newly completed reservoir sits just south of the existing tank McCarthy constructed nearly 20 years ago. Measuring approximately 234 feet by 234 feet and 25 feet tall, the structure required about 8,300 cubic yards of concrete and careful sequencing to accommodate expansion joints. The close proximity to existing infrastructure, including a live fiber-optic duct bank, required extensive virtual design and construction modeling, deep excavation and specialized shoring systems.
“From the deep excavation and complex shoring to the leak-detection system and elevated deck, the team found solutions and delivered a high-quality structure on a very tight site while keeping the plant fully operational the entire time,” said Gray Wensley, senior superintendent for McCarthy’s Water team, in a press release.
To address soft soils and historic settlement concerns, the City adopted a sub-slab leak-detection system beneath the reservoir to help staff identify potential leaks quickly.
“This reservoir is a critical piece of our long-term water operational strategy for the East Valley,” said Chris Hassert, City of Mesa Water Resources Director, in a press release.
Phase II is expected to complete in early summer 2027 and will double the plant’s treatment capacity from 24 mgd to 48 mgd, adding advanced treatment, disinfection and solids handling improvements to support future growth.