A Review on In - Situ Chemical Oxidation and Heterogeneity

Chemical oxidants are increasingly being used for in-situ destruction of organic contaminants in ground-water. The most common implementation involves using an injection/withdrawal system to circulate oxidants (e.g., potassium permanganate, hydrogen peroxide, and Fenton’s Reagent) through a DNAPL-source zone. Since the efficiency of chemical oxidation is highly dependent on geological heterogeneities, effective delivery schemes are essential for successful remediation. This paper reviews the impact of heterogeneities on the success of in-situ chemical oxidation. Physical heterogeneities are primarily concerned with the permeable pathways along which oxidants are transported to the zone of contamination. Chemical heterogeneities refer generally to variability in geochemical-related properties that also bear on the efficiency of oxidant flooding. Both types of heterogeneities work against bringing the oxidant to zones of high contaminant saturations. The highly heterogeneous distribution of contaminants and difficulties in characterization make it difficult to target specific zones for treatment. As a result, large volumes of sediments will be often treated whether contaminated or not. Heterogeneities in hydraulic conductivity at most sites provide intensive dose of chemical reagents into permeable pathways and little treatment of low conductivity zones. Large quantities of oxidizable materials in the geologic units are capable of consuming the oxidant during delivery. Reaction products (e.g., CO2, MnO2, Fe(OH)3) tend to plug the porous medium, especially in zones with large contaminant saturations. The oxidant flood is diverted away from these zones making the flooding inefficient. The efficiency of oxidant injection can be deteriorated and subsequent developments to overcome these problems are required.