General contractor McCarthy Building Companies Inc. (McCarthy) continues work on the $168 million expansion of the Signal Butte Water Treatment Plant in Mesa, Arizona. The team broke ground in January 2024, and the project is expected to complete in the summer of 2027.
The team split the expansion into two phases. Phase one included constructing an 8-million-gallon potable water reservoir and redundancies to ensure system reliability and provisions for the plant’s future expansion. Phase two will double the plant’s water treatment capacity from 24 million to 48 million gallons per day (MGD) and will enhance plant operations and resiliency for Mesa’s growing East Valley service area.
The team broke ground on phase one in January 2024, while preconstruction began on phase two. Black & Veatch designed the reservoir, which is 234 feet by 234 feet and 25 feet tall. McCarthy was selected as the general contractor through a construction manager at-risk (CMAR) contract at 30 percent designed. The CMAR contract allowed McCarthy to enter the design conversation early in project planning, which was critical to the success of the complex project because it allowed the team to preemptively address challenges.
“Early engagement enabled us to develop a comprehensive plan, gain a clear understanding of the construction requirements, and create a schedule that incorporated every tie-in,” said Oscar Munoz, Project Director for McCarthy Building Companies Water Group. “We leveraged our in-house resources to develop a detailed construction plan early, ensuring we had a clear path before engaging trade partners.”
Constructing the reservoir required excavating approximately 8,300 cubic yards of material to match the depth of an existing reservoir, also constructed by McCarthy nearly two decades ago, just 12 feet from the new reservoir.
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| Ring Power Corporation |
| Ring Power Corporation |
The construction team reviewed as-builts for utilities to understand their location and created plans for rerouting some utilities and shoring others to prepare for the new reservoir. The team drew from its experience constructing the existing reservoir, as well as success on similar projects, to make design suggestions to improve constructability and logistics on the small site, and to save costs for the City of Mesa.
“Through coordinated efforts between McCarthy, Black & Veatch, and the City of Mesa, our team optimized the influent piping and reservoir walls, delivering savings for the city,” said Matthew Schmidt, Project Manager for McCarthy Building Companies Water Group.
Arizona soil conditions typically require a 2:1 excavation slope. For this site, that ratio was too large, as there were only about 12 feet separating the new and existing reservoirs, with a live fiber-optic duct bank and nearby structures in between. To safely work within the limited space, McCarthy engaged a specialist engineer to design a reduced 1.5:1 slope on three sides of the excavation, with a soil nail shoring system implemented on the north side.
“Given the existing structures around the reservoir, we developed a plan to reduce the footprint and provide access via a ramp on the south side,” Munoz said.
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| Linder Industrial Machinery |
| Linder Industrial Machinery |
McCarthy used VDC modeling to plan shoring, slopes, and crane locations to excavate the site without impacting existing infrastructure.
The excavation extended roughly 30 feet below grade. To save on hauling and storage costs associated with the excavated material, McCarthy worked with the City of Mesa to store 20,000 cubic yards of soil in an adjacent park.
Once excavated, McCarthy’s team installed a layer of #57 rock under the footprint of the future tank, executing Black & Veatch’s design. Perforated pipe was placed in four quadrants and tied back to a sump, allowing city staff to pinpoint the source area if a leak were to occur in the future. Geofabric was then placed over the rock and piping.
The sub-slab system required civil and concrete crews to carefully place and shape the rock and geotextile fabric, primarily by hand, in accordance with Black & Veatch’s specifications. McCarthy’s concrete team poured concrete for the reservoir in 40-foot by 40-foot squares sequenced diagonally to allow for expansion joints. Gaining access to the adjacent park opened access to the reservoir, which sped up the concrete schedule.
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| Dobbs Equipment (DXC) |
| Dobbs Equipment (DXC) |
“During excavation, we approached the city to explain that access from only one side was limiting constructability and proposed that we could provide additional value if we were allowed to use a portion of the park for staging and access,” Munoz said. “Access to the park allowed us to reach the site from three sides, enabling multiple pours to be completed simultaneously and providing space to store soil that would be needed later.”
The team installed specialized soil-nails with shotcrete shoring and engineered beam supports to protect the live fiber-optic duct bank while crews tied in new piping below and connected it to the facility.
McCarthy completed the reservoir at the end of 2025, two months earlier than anticipated. The early completion is due to the construction team being highly involved in the design of the new and existing reservoir, access to the park, and finding unique ways to commission equipment earlier than scheduled.
“Many team members were part of preconstruction, and we carried that team into field operations and the execution of work,” Schmidt said. “This results in a seamless transition, as team members are familiar with the project and able to reflect on past conversations and agreements.”
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| Linder Industrial Machinery |
| Linder Industrial Machinery |
With the reservoir complete, McCarthy is working on the next phase, which includes expanding the plant from 24 MGD to 48 MGD along with infrastructure for system redundancies, improved operations, and increased resiliency — while keeping the plant operational.
“One of the main challenges is working on an active plant while executing more than 150 maintenance and plant operations [MOPO],” Schmidt said. MOPOs are critical system tie-ins and installations that occur while the plant is still operating.
The team creates a plan specific to each MOPO, which requires working closely with other stakeholders like the City of Mesa and Black & Veatch. The city schedules two water treatment plant shutdowns each year, and McCarthy aims to schedule many MOPOs during those times to avoid conflicting with plant operations. One of the shutdowns occurred in spring 2026.
During shutdown periods, the team takes advantage of every minute to complete MOPOs, and they meet daily with the City of Mesa to discuss progress.
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| Pinnacle Central Co Inc |
| Pinnacle Central Co Inc |
“Executing those plans is a team effort, with proactive communication, transparency, and alignment,” Schmidt said. “We plan well in advance to look at all tie-in points with the city, ensuring transparency on procurement status and the progress of each MOPO.”
Phase two will double the plant’s water treatment capacity and includes adding a mirrored sand-ballasted flocculation, ozone generation, and sodium hypochlorite generation disinfection process. It also improves solids handling and adds six filters.
The ozone system is the “heart of the plant,” according to Schmidt. The team was unable to use the same ozone system manufacturer as the original phase, creating a significant integration challenge. Through close coordination and ongoing design efforts, the team is working to implement a new system that fully integrates with the existing technology.
“We needed to be sure we could integrate two systems to make sure they would be fully functional,” Schmidt said. “It takes a lot of coordination between the new vendor and the existing vendor, getting cooperation from both ends to deliver fully coordinated systems.”
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| Linder Industrial Machinery |
| Linder Industrial Machinery |
The team meets weekly with the vendors to coordinate the integration, as well as a third-party programmer to ensure system reliability.
McCarthy recently poured concrete for two main structures, an approximately 13,500-square-foot water treatment complex and a more than 9,000-square-foot filter complex. The facilities required a total of more than 5,000 cubic yards of concrete.
The concrete pours for the structures in phase two took place during Arizona’s unseasonably hot conditions, with temperatures regularly exceeding 100 degrees Fahrenheit. To manage the heat, the team coordinated with the concrete supplier, City of Mesa inspectors, and plant operations to begin pours at 2 a.m.
“Managing the concrete temperature requires an ever-changing ratio of nitrogen and ice,” Schmidt said. “That’s where having McCarthy’s full team of concrete experts provides a real advantage.”
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| Beard Equipment Co - AL |
| Beard Equipment Co - AL |
| Tractor & Equipment |
| Tractor & Equipment |
To successfully deliver such a complex project, McCarthy relies on continuity in team members, high levels of experience in its workforce, and constant communication among all project stakeholders.
"There are team members who built the original reservoir 20 years ago, and that familiarity greatly benefits our work here,” Schmidt said. “Additionally, many of our team members and superintendents have built similar structures and bring valuable experience to the project."
The team expects to deliver phase two in the summer of 2027. The original water treatment plant opened in 2018 and was master planned to accommodate future expansions as demand grew in southeast Mesa. This project marks the first expansion.
- Ozone system/ballasted flocculation by Veolia Water
- Sludge thickener equipment by WesTech
- Plate settler treatment by WesTech
- Sodium hypochlorite by DeNora
- Vertical diffusion vane pumps by Trillium
- General Contractor: McCarthy Building Companies Inc., St. Louis, Missouri
- Engineer of Record: Black & Veatch, Overland Park, Kansas
- Electrical: Industrial Power Solutions LLC, Glendale, Arizona
- Concrete Reinforcing: Suncoast Post Tension, Phoenix, Arizona
- Shoring: Buesing Corp., Phoenix, Arizona Photos courtesy of McCarthy Building Companies
