Jean-Claude J. Bonzongo, PI
Timothy G. Townsend, co-PI
Akua B. Oppong-Anane, PhD Candidate

University of Florida

Anomalously high iron (Fe) concentrations have been reported in groundwater monitoring wells at landfill sites at a number of both lined and unlined facilities in Florida. Based on water quality monitoring data, the native vadose zone soils beneath the landfills and/or the aquifer sediments are likely the main sources of the observed Fe pollution. This is because groundwater samples collected from wells near some of these impacted landfill sites show little to no evidence of tracers of landfill leachate contamination.  In Fe-rich soils found under unlined landfills, reducing conditions could develop as a result of leachate migration into the vadose zone, and/or the diffusion of landfill gases into the pores of heterogeneous unsaturated soils, leading to the reduction of iron previously locked into Fe-(hydr)oxide minerals and transfer to the aqueous phase as Fe2+(aq). However, for sites impacted by lined landfills, it is likely that the reducing conditions and the resulting dissolution of Fe could be attributable to several factors including: (i) changes to the natural hydrology that result from the use of impermeable liners which cut off water infiltration pathways through the vadose zone and oxygen replenishment via rainwater; and (ii) potential leaks of landfill leachate over time, enough to induce reductive dissolution, but without significant leachate contamination signature in the impacted groundwater.  The objective of this research was therefore to investigate the role of selected critical parameters driving the reductive dissolution of Fe, and ultimately, to use obtained results to develop a predictive tool for the determination of the adequacy of soil sites for landfill use.

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