Reduced Permeability in Groundwater Remediation Systems: Role of Mobilized Colloids and Injected Chemicals

The success of pump-and-treat or in situ remediation of contaminated aquifers depends in part on the ability to maintain the permeability of the aquifer, withdrawal wells, and delivery systems at a reasonable cost while moving significant quantities of water. We have considered one case in which a previous bioremediation effort at Eglin Air Force Base in Florida was halted due to delivery system failure at tributed to iron precipitation. Laboratory solutions and groundwaters from the Eglin site were passed through packed columns of aquifer material also obtained from the site. We investigated the effects of iron oxidation state and concentration, the pres ence of colloidal materials, and the effects of nutrient solutions and hydrogen peroxide in the feedwater on the permeability of the aquifer material. Our experi ments show that reduced permeability of the aquifer near delivery systems was likely caused by the re-deposition of colloids mobilized in the aquifer and by gas binding due to bacteriologically catalyzed hydrogen peroxide decomposition rather than to iron precipitation.