Tres Rios Water Reclamation Facility


Using the construction management at-risk delivery method, MWH Constructors provided Pima County with preconstruction and construction services to upgrade an existing operational pollution control facility.

Pima County | Tucson, Arizona


Project Overview

MWH Constructors was the construction manager at-risk (CMAR) on this plant expansion project, increasing capacity from 37.5 to 50 mgd, and upgrading an outdated plant with a state-of-the-art water reclamation plant. The new facility produces high quality effluent that is used to water parks and other areas, which is an important consideration for this desert community. This fast-tracked project included two new digesters, a new blower building, and a new 25-mgd ammonia/nitrogen/nutrient removal process system (5-stage Bardenpho) to replace an existing 25-mgd HPO train.The 5-stage Bardenpho aeration process biologically removes not only organic matter, but also nitrogen and phosphorous from the wastewater stream. MWH Constructors was responsible for self-performing procurement, installation of process piping and equipment, instrumentation and control, and commissioning and startup. This project addressed a long-standing community issue, as well, involving nuisance odors emitted from various Pima County wastewater treatment facilities. MWH Constructors developed a system-wide odor control master plan that called for state-of-the-art odor control systems.

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Aerial image of Tres Rios

 Project Scope

All construction activities took place within an existing operational plant. The project team successfully addressed safety concerns including lock-out/tag-out procedures, fall protection, trenching and excavation, and working in confined spaces while maintaining the safety of the plant staff. Also, during the design phase, the project team discovered that parts of the plant were sitting on a veritable historical treasure: an irrigation and canal system dating back to the San Pedro period, between 1250 B.C. and 750 B.C. An archeological team was brought in to evaluate and document the 3,000-year-old findings, which increased their understanding of the life ways of the ancient people of the Tucson Basin in what Archaeology Magazine named one of the top 10 finds of 2009.

Millions of dollars in savings

Electrical switchover tie-ins without incident

Artifacts donated to Arizona State Museum

Mechanical tie-ins without incident

“Overall, the [ROMP Ina Road Expansion Project] was a success! The team completing this job was the right team for the job.”

Jaime Rivera

Program Manager, Pima County