Executive Summary
Currently over 600 million tons of phosphogypsum, hydrated calcium sulfate produced as a by-product during the manufacture of phosphoric acid, are stockpiled on the ground in Florida. The material could represent a significant resource if practical and environmentally sound uses could be found for it. One possibility is in the construction of roads, where it might be used in pavement, as fill, or especially in the road base. In order to determine the engineering properties of phosphogypsum in roads, and to determine any impacts of its use on the local environment, in 1986-87 two test roads were built incorporating the material. White Springs Road in Columbia County and Parrish Road in Polk County were reconstructed by local authorities, working under the guidance of the Civil Engineering Department of the University of Miami. Their research showed first that phosphogypsum was a suitable building material from an engineering standpoint. To determine any environmental impacts, chemical or radiological, studies of air, groundwater and soil were done by the university before and after construction. Monitoring wells were drilled to the surficial aquifer along both sides of both roads, and water samples collected monthly to define over two dozen parameters, including radium. Since phosphogypsum is known to be elevated in radium content as compared to background soils in Florida, in addition to water radium the research included measurements of soil radium, air and soil radon gas, and gamma radiation at both sites. The university work showed that the presence of the phosphogypsum did not cause any appreciable change in the quality of air, soil, or water at the local sites.
The question arose as to whether or not there might be any long-term trends in environmental quality caused by the phosphogypsum used in the roads. Thus the environmental studies established by the university were continued for an additional 2 and 1/2 years by the staff of the Institute. Site visits were made every 2 or 3 months from mid 1988 to late 1990, with air, water and soil being tested for the same chemical and radiological parameters as studied by Miami. Whereas the university had focused on a comparison of parameter levels before and after road construction, the work of the Institute focused on changes in parameter levels over time. In Polk County, during the last year of the Institute’s work, water contaminants in the lakes on either side of Parrish Road were determined and compared with groundwater results. A comparison of levels found with water quality standards also was made when possible. Trends were determined by plotting parameter levels, mainly in water but also in air and soil and for external gamma, against elapsed time since the inception of the Institute work. Regression lines were calculated for each parameter at each well, and for parameters at all other air and soil monitoring sites except for soil radium. Whenever the slope of any line differed significantly from zero, i. e. from the horizontal, then a trend was said to exist.
Trends data are presented in several manners. They are summarized for all wells, for “inner” versus “outer” wells, and for wells lying east of each road versus those lying west. Finally, individual trends data are presented for water parameters that might be indicative of phosphogypsum, i. e. calcium, sulfate, fluoride, and radium. Trend analyses were also performed for gamma, both on and adjacent to each road, and for air and soil radon. All data are summarized in both tabular and graphical forms in this report, and additionally all data points are provided in the Appendix.
For the majority of parameters at the majority of sampling locations, no trends were established over the 2 and 1/2 years of the study. Levels found were highly variable in time and space, and random differences generally more pronounced than differences associated with elapsed time. However, in Polk County most wells showed an upward trend in calcium, possibly indicative of some leaching of phosphogypsum into the groundwater, but possibly influenced by high levels of calcium in the lakes on both sides of the road. Trends in sulfate were both up and down; hence not necessarily indicative of leaching, although in Polk County groundwater sulfate was higher than that found in the adjoining lakes. There were far fewer trends for the other contaminants, with many of those that were seen being downward. Trends among wells in Columbia County were fewer, more random, and more mixed than in Polk. Drinking water standards exist for 14 of the water analysis studied. These were exceeded often for iron and pH, and sometimes for manganese, but rarely exceeded for anything else, including phosphogypsum constituents. The few exceptions were for individual data points, not averages. Trends in air and soil radon were not significant at either road; levels found at Parrish Road were typical of background in the vicinity of mineralized lands, and at White Springs Road were typical of the Florida background. Soil radium levels found were typical of levels expected in the two areas. Direct gamma over the pavement was elevated at both roads as compared to readings taken adjacent to the roads, but still typical of background in the respective areas. Average gamma levels at all locations were below limits for indoor residential exposure as recommended by the Florida Department of Health and Rehabilitative Services.
Gordon D. Nifong and Jon K. Harris - Florida Institute of Phosphate Research