MITIGATING FOUL ODORS FROM AN AGING WASTEWATER STRUCTURE NEAR A POPULAR PARK

In northern Tucson, just steps away from the popular Rio Vista Natural Resource Park, nearly 25 million gallons of wastewater flow through the Tucson Boulevard Diversion Structure each day. This key structure helps Pima County Wastewater Reclamation manage and balance flows between two major interceptor sewers, allowing the County to accommodate growth and maintenance.  

After decades of use and modifications, the existing diversion structure became an odorous, corroded, and dangerous facility to manage. Park-goers and residents in the area complained about the odor, which was more than a nuisance; it was a symptom of the excessive hydrogen sulfide (H₂S) gas produced within the structure, where the corrosive, noxious gas wreaked havoc. The corroded diversion gates became non-functional, and entering the structure to adjust flows required extensive safety precautions. Addressing these issues—odor, corrosion, and safety—was a top priority for the County.  

In the existing system, multiple flow activities occurred in a single confined space—bends (including a tight 90-degree bend), expansions, contractions, and merging flows—all at high flow rates. This configuration created a roaring turbulent mix that produced excessive amounts of H₂S gas.

To address this root issue, Dibble designed a new system that substantially improves hydraulic performance. Bends and diversions now occur in three separate structures, and the diversion structure is designed so flow normally stays below the diversions. This design approach reduces energy losses, turbulence, and off-gassing, which in turn mitigates odors, reduces corrosion, and improves safety.

To further avoid corrosion, the new structures are constructed of innovative non-corrosive materials including pre-cast polymer concrete and fiberglass. Dibble also designed the new diversion structure with stop gates accessible through a large access hatch. Operating the stop gates no longer requires a confined space entry into a potentially hazardous environment, and the new structure is safely maintainable.  

This massive, complex new system required close coordination among the County, Dibble, and Hunter Contracting Co. (CMAR) throughout design and construction. Extensive wastewater bypass, tight workspace, and unexpected soil conditions made installation complicated. But working together, the team overcame supply chain issues, mitigated permitting challenges, and minimized bypass pumping duration.

This award-winning project was completed on time and within budget, with minimal inconvenience to residents and businesses. Now the County and the community can breathe easily, and the new Tucson Boulevard Diversion Structure can provide value for decades to come. 

Project Lifecycle