The International Information Center for Geotechnical Engineers

Soil Remediation Techniques: Examination of In Situ Chemical Oxidation

 

1. Introduction

In Situ Chemical Oxidation (ISCO) is the procedure in which a chemical oxidant is introduced into the site’s subsurface with the purpose of transforming groundwater or soil pollutants into safer species (Hueling & Pivetz, 2006).  Through chemical oxidation the oxidation state of a substance is decreased by accepting an electron to oxidize the target species. The target species is then put in a oxidized state which can eliminate the toxicity of the original contaminant. 

Figure 1 provides a simple example of an oxidation-reduction reaction where copper is being reduced by gaining electrons and Magnesium is being oxidized by giving its electrons to Copper. This redox reaction is what takes place in the field with the addition of an oxidant. The oxidant being introduced into the field would act as the Copper by accepting electrons from the contaminant which then oxidizes to a less harmful species. It should be noted that there is In Situ Chemical Reduction Technology available as well in which the chemical introduced would reduce the contaminant into a safer species.

Figure 1Figure 1: Oxidation Example (Clark, 2013)

 

ISCO technology is appealing as this reaction takes place in the field without the direct removal of the contaminant from the soil or groundwater. The four major oxidants used for ISCO are permanganate, persulfate, hydrogen peroxide, and ozone (Watts & Teel, 2006). Site characterization is critical for using the proper oxidant and implementation method.  A complete understanding of the soil properties, hydrogeology, and geochemistry is essential for successful remediation using ISCO technology. The main target of ISCO remediation techniques are organic chemicals (Hueling & Pivetz, 2006). ISCO is typically used where contaminant concentration is high and it is usually introduced to the contaminant by pumping the oxidant into wells in the contaminated area.  Figure 2 depicts the process of injecting an oxidant into a contaminated area.

Figure 2Figure 2: In Situ Oxidation Application (Groundsure 2005)

Bench-scale studies can be useful in selecting the appropriate ISCO technique to be used. Although these studies can offer valuable insight to technique feasibility, its limitations in relation to field-scale studies need to be recognized and its results heavily analyzed (Hueling & Pivetz, 2006). In addition, pilot-scale studies are used when a larger volume of soil or groundwater needs remediation (Hueling & Pivetz, 2006). These help with the design and implementation of the final full-scale ISCO application.

The response time associated with this methodology is dependent upon numerous factors from the contaminated area, such as homogeneity of the soil, hydraulic conductivity and soil characteristics, groundwater flow or water table, and the longevity of the specific oxidant being used. This can be on the order or a few months to several decades resulting from a combination of these factors. 

A detailed assessment of ISCO performance evaluation and rebound is necessary during and after remediation is completed. Hence, monitoring plays an important role in the final remediation results.

Permitting is generally not extensive for ISCO deployment. Regulatory issues associated with ISCO include state or federal programs associated with underground injection control and air quality (Interstate Technology and Regulatory Council, 2005). Each oxidant has health and systems specific to each and should be treated as such. Some oxidants are more hazardous than others such as permanganate and persulfate dust. With ISCO technology, there is potential for uncontrolled exothermic reactions or migration of oxidants and/or contaminants (Interstate Technology and Regulatory Council, 2005).

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