Modified Fenton's processes for effective in‐situ chemical oxidation—Laboratory and field evaluation

Fenton's reagent in its conventional form, although effective for contaminant treatment, is impractical from an in-situ field application perspective due to low pH requirements (i.e., pH 3-4), and limited reagent mobility when introduced into the subsurface. Modified Fenton's processes that use chelated-iron catalysts and stabilized hydrogen peroxide have been developed with the goal of promoting effective in-situ field application under native pH conditions (i.e., pH 5-7), while extending the longevity of hydrogen peroxide. Laboratory experiments conducted in soil columns packed with organic soil to compare modified Fenton's catalysts with conventional catalysts (acidified iron [II]) indicated superior mobility and sorption characteristics for modified Fenton's catalysts. Furthermore, the acidic pH of a conventional catalyst was buffered to the native soil range, leading to increased iron precipitation/adsorption following permeation through the soil column. The chelates present within the modified Fenton's catalyst showed greater affinity toward iron compared with the native soil and, hence, minimized iron loss through adsorption during the permeation process even at pH 5-7. Field effectiveness of the modified Fenton's process was demonstrated at a former dry-cleaning facility located in northeast Florida. Preliminary laboratory-scale experiments were conducted on soil-slurry and groundwater samples to test the process efficacy for remediation of chlorinated solvents. Based on successful experimental results that indicated a 94 percent (soil slurry) to 99 percent (groundwater) reduction of cis-1,2-DCE, PCE, and TCE, a field-scale treatment program was initiated utilizing a plurality of dual-zone direct push injection points installed in a grid fashion throughout the site. Results of treatment indicated a 72 percent reduction in total chlorinated contamination detected in the site groundwater following the first injection event; the reduction increased to 90 percent following the second injection event. © 2002 Wiley Periodicals Inc.