The closed phosphogypsum stack is located in Polk County, Florida. As much as 140-foot high unlined stack had been used for over 30 years to accept phosphogypsum, a byproduct of the fertilizer production process. The stack system, comprising about 900 acres, included a series of process acid water ponds at-grade and on top of the stacked phosphogypsum, and these ponds comprised a large portion of the process system watershed. In order to reduce the source of potential surface and ground water contaminants from the stack, and to reduce the process system watershed on the site, a closure plan was implemented for the stack system. Ardaman & Associates, Inc. assisted throughout the permitting process, providing recommendations for various environmental solutions and design. Ardaman designed the closure plan and assisted in developing a comprehensive and creative process water management plan and innovative phased construction management and scheduling for the stack/pond system. Ardaman also provided QA/QC testing and inspection of all the project elements during construction.

As a result of the closure, the entire contaminated stack system watershed was eliminated (about 800 acres) and the acidic process water inventory was reduced by more than 92% to-date, which included 100% reduction of ponded process water (about 1.9 billion gallons) and more than 78% reduction in water within the pores of the gypsum (about 900 million gallons). Further, the pollutant discharges from the site were all reduced dramatically as the closure progressed. This project is one of the largest phosphogypsum stack system closures in the world.

The project was selected for an Honor Award by the Florida Institute of Consulting Engineers as part of their Engineering Excellence Awards program.