In situ chemical oxidation, or ISCO, is one of the more rapid methods for treating subsurface contamination. Sites with contaminated soil and groundwater are a serious concern in the U.S. and around the world; tens of thousands of such sites exist, often the result of improper or illegal disposal of hazardous wastes such as chlorinated dry cleaning solvents, gasoline, dioxins, or PCBs.
In situ means in place; ISCO treatments are injected into the ground through wells to destroy contaminants within the subsurface, without the need to excavate contaminated soil or pump out contaminated groundwater for treatment. Chemical oxidation refers to the type of chemical reaction that is common to all ISCO processes; it can be defined as a loss of electrons or a gain of oxygen. Oxidation transforms organic contaminants into other, usually less hazardous compounds, including water and carbon dioxide. The four most common ISCO technologies are permanganate, ozone, activated persulfate, and CHP, which stands for catalyzed H2O2 propagations or catalyzed hydrogen peroxide and was formerly known as modified Fenton’s reaction. ISCO treatment is usually more rapid than alternative processes such as pump-and-treat, bioremediation, natural attenuation, air sparging, or soil vapor extraction.
Our research has shown that in addition to chemical oxidations, activated persulfate and CHP ISCO processes also include chemical reductions and nucleophilic substitutions among their mechanisms, which broadens the range of contaminants they are able to treat. These ISCO processes have also been shown to treat difficult or recalcitrant contaminants, including highly oxidized compounds, sorbed contaminants, and contaminants found in dense nonaqueous phase liquid (DNAPL) pools.
For a more detailed overview of the four major ISCO technologies, please see our review article:
Watts, R. J., Teel, A. L., 2006. Treatment of contaminated soils and groundwater using in situ chemical oxidation. Pract. Period. Haz. Waste Manag., 10(1), 2–9
and the recent book:
In Situ Chemical Oxidation for Groundwater Remediation (SERDP/ESTCP Environmental Remediation Technology Volume 3). R.L. Siegrist, M. Crimi, and T.E. Simpkin, Eds. Springer, 2011.