Tucson Boulevard Diversion Structure


Award of Merit, Water/Environment

Submitted By: Hunter Contracting Co.

Owner: Pima County, Ariz.

Lead Design Firm: Dibble

General Contractor: Hunter Contracting Co.

When a rotten egg odor began plaguing the El Rio Vista Natural Resource Park, local officials realized that it was coming from a Pima County wastewater sewer structure, which had undergone numerous modifications over the last 50 years. The structure featured a 90-degree bend and six sewer connections of varying diameters, resulting in turbulent flows, eddies and persistent odor problems.

The project team set out to replace the aging diversion structure, where prolonged exposure to excessive hydrogen sulfide gas had caused extensive corrosion, compromising the concrete and rendering the motor-operated stop gates dysfunctional. An outdated system also required risky confined space entry, exposing personnel to potentially lethal mixtures of toxic gasses, including hydrogen sulfide and methane.

During the excavation and exposure of the tie-in point, the contractor discovered a significant misalignment between two pipes. To rectify this issue, crews chased the existing pipe back to the manhole and removed the misaligned 54-in. RCP and 48-in. Hobas pipe at the downstream end. Then, approximately 35 ft of new 48-in. Hobas pipe followed in a straight run, reconstructing the inverts of each manhole with polymer grout for a smooth flow transition. This ensured sewer line alignment, enhancing the overall efficiency and functionality of the system after work was completed in July 2022.