The city of Goodyear, Ariz., is home to Arizona’s largest municipally owned and operated reverse osmosis plant, which treats 3.5 million gal per day (mgd) of drinking water. That treatment also produces 500,000 mgd of brine concentrate, composed of 9,000 to 11,000 ppm salinity and containing high concentrations of arsenic, fluoride, nitrates and selenium.
Due to pollution controls, the brine cannot be discharged into U.S. waters. The plant previously sent the brine to the city’s reclamation facility, hampering operations and monopolizing space for new development. It was time for another tactic.
Out of the many options Goodyear considered for disposing of the brine—including pumping it to the Yuma, Ariz., desalting plant, deep well injection, evaporation ponds, and more—the city decided on wetland disposal because of its cost-effectiveness and ease of operations and maintenance.
With help from the U.S. Bureau of Reclamation, the city decided to place the wetlands in the Maricopa County Estrella Mountain Regional Park, which offered enough space for 30 acres of constructed wetlands, and embraced the addition of a lake that would be used for blending the brine water.
While the wetlands remove selenium, arsenic and nitrates from the brine, evaporation and transpiration increase its salinity as it flows through them. The engineering team required a strategy to blend the water to ensure its quality prior to discharging it into the Gila River.
The project team chose three means of blending: remediated groundwater, reclaimed water and underground storage. To complicate the situation, each of these water supplies originated in different areas of the city of Goodyear, thereby requiring several infrastructure systems for delivery and pretreatment them before blending them with the wetland discharge.
Other challenges during the project included engineering the wetlands so they could be easily removed and replaced when they became saturated, and obtaining the federal and state permits needed for the Gila River discharge.
In addition to nutrient removal, the wetlands offer environmental benefits, including enhancing the river environment and river water quality; keeping the river channelized; abating invasive salt cedar trees; and helping with flood control.
On top of these benefits, the project also will provide recreational and educational benefits to Goodyear residents. Pedestrians can walk and bike in the wetlands area and interpretive kiosks and signage also will be available. Graduate students from Arizona State University, the University of Arizona and Northern Arizona University will have the opportunity to conduct research at the wetlands. Lastly, as wetlands are attractive to bird life, birding opportunities will be plentiful.