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 An outdated system also required risky confined space entry, exposing personnel to potentially lethal mixtures of toxic gasses, including hydrogen sulfide and methane.