A significant upgrade to the original facility, this new plant serves the water reclamation needs of the city of Mesa and the towns of Gilbert and Queen Creek, Ariz. The construction manager at-risk project was one of the largest recent municipal wastewater capital improvement projects in the Southwest, requiring 66 months to complete. The scope called for replacing nearly all of the aging infrastructure and installing new structures. Each of the two 66-ft-dia, egg-shaped digesters required significant structural concrete work—3 ft thick and 36 ft tall. The ground slab for these walls was 4 ft thick and 86 ft in diameter.

Photo courtesy of Carollo Engineers Inc.

As an end-of-the-line plant, it was imperative that operations be maintained through all phases of the project. Further complicating this challenge was the replacement of existing programmable logic controllers (PLCs) and variable frequency drives (VFDs), which was done at the same time as installation of new infrastructure to support the expanded facility. Approximately 20 PLCs and 60 VFDs were replaced and reprogrammed.

Photo by Tim Roberts Photography

In addition, COVID-19 required safety protocols and caused interruptions because of supply-chain impacts, resource limitations and travel restrictions. Still, the project, which required 1 million worker-hours, met all regulations and was completed on time and under budget in November 2020 without any unplanned outages.