Chemical oxidation uses chemicals called “oxidants” to help change harmful contaminants into less toxic ones. It is commonly described as “in situ” because it is conducted in place, without having to excavate soil or pump groundwater for aboveground cleanup. In situ chemical oxidation, or “ISCO,” can be used to treat many types of contaminants like fuels, solvents and pesticides. ISCO is usually used to treat soil and groundwater contamination in the source area where contaminants were originally released. Following ISCO, other cleanup methods, such as pump and treat or monitored natural attenuation, are often used to clean up the smaller amounts of contaminants left behind.