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GEOCHEMISTRY OF SUBSURFACE REACTIVE BARRIERS FOR REMEDIATION OF CONTAMINATED GROUND WATER
Wilkin*, R T. GEOCHEMISTRY OF SUBSURFACE REACTIVE BARRIERS FOR REMEDIATION OF CONTAMINATED GROUND WATER. Presented at Department of Geosciences, Texas Tech University, Lubbock, TX, 10/13/00.
Reactive barriers that couple subsurface fluid flow with a passive chemical treatment zone are emerging, cost effective approaches for in-situ remediation of contaminated groundwater. Factors such as the build-up of surface precipitates, bio-fouling, and changes in subsurface transport control long-term performance of such Permeable Reactive Barriers. Surface precipitates can impact long-term performance by decreasing iron reactivity, and by decreasing pore space/permeability that may result in detrimental rerouting of subsurface flow paths. Reactive barriers containing zero-valent iron alter ambient groundwater chemistry by increasing pH, PH2, and decreasing the oxidation-reduction potential. Depending on the composition and oxidation state of ambient groundwater, these conditions can favor the precipitation of mixed iron oxyhydroxides, Ca-Fe carbonates, magnetite, or mixed valence Fe(II)/Fe(III) ternary compounds (such as green rusts). In sulfate-rich groundwaters, reducing conditions promote microbial sulfate reduction and the precipitation of iron monosulfides. Results are presented of long-term monitoring studies (groundwater chemistry and soil/iron characterization) from PRBs at two different PRB systems, each with contrasting groundwater compositions