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Abstract. The Toxic Substance Control Act (TSCA) of 1976 authorizes the Environmental Protection Agency (EPA) to obtain production and test data from industries on selected substances and mixtures, and to regulate these substances when needed. Currently, phosphogypsum, a waste byproduct of phosphate ore processing, is being regulated under TSCA. To obtain a better understanding of the environmental effects caused by phosphogypsum stacks, the Tuscaloosa Research Center investigated the effects of a synthetic rainwater and a process cooling pond water on the mobility of metal and nonmetal ions through an inactive phosphogypsum stack in Florida. Twenty-one groundwater monitoring wells were installed in a 160 acre, 30 year old inactive phosphogypsum stack in the Central Florida Phosphate Mining District. The wells were placed in the stack in clusters of three, with the wells being 17, 27, and 37 ft deep, respectively. ·well core samples were taken every 5 ft for characterization studies and column leaching tests. These wells were monitored monthly with samples analyzed for pH and metal and nonmetal ion concentrations. Two leach solutions, a synthetic rainwater to simulate natural rainfall and a phosphate plant process cooling pond water were used in the laboratory column leaching experiments. Leachate from these column leaching tests using phosphogypsum from the well cores was found to contain metal and nonmetal ions. Such tests indicate that metal and nonmetal ions contained in the phosphogypsum have the potential for migrating into surrounding surface waters and groundwater.

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