Since 1964, the city of Mesa, Arizona, has been required by the regional wastewater treatment authority to control dissolved sulfides in wastewater to a maximum of 0.5 mg/L. By 1983, the original sulfide control facility was outdated, undersized, and costly to operate. Modeling and wastewater analysis indicated that summertime flows could contain as much as 5 mg/L sulfides–10 times the allowable level. Evaluation and bench-scale testing of 12 chemicals and chemical combinations indicated that ferrous chloride (FeCl2) was the most cost-efficient sulfide control chemical for Mesa. The prototype control station, designed to feed bulk FeCl2 to the sewers, began operation in late 1985. The station was so effective at controlling dissolved sulfides below the 0.5 mg/L limit that Mesa had two similar stations constructed in 1987 to protect other portions of its sewers.