The International Information Center for Geotechnical Engineers

Soil Remediation Techniques: Examination of In Situ Chemical Oxidation

 

4. Site and Contaminant Compatibility

The appropriateness of ISCO technology is dependent on the effectiveness of, and ability to control the ISCO reaction with contaminants and the effective delivery of the reagents to the zone to be treated (Interstate Technology and Regulatory Cooperation Work Group, 2001). Depending on the choice of oxidant and site conditions, the natural oxidant demand can be several times the target compound oxidant demand. 

 

Total Oxidant Demand = Target Compound Oxidant Demand (soil+water) +Natural Organic Oxidant Demand + Natural                                                             Inorganic Oxidant Demand                                                                 (19)

 

When determining if a site is feasible for ISCO technology, careful site characterization and screening test should be performed. Specifically, test for hydraulic conductivity and test for heterogeneity within the contaminated zone should be undertaken. A hydraulic conductivity of greater than 10-7 cm/sec is recommended (Interstate Technology and Regulatory Council, 2005). This is important because lower hydraulic conductivity can cause pockets of untreated contaminants within the area being remediated. When applying liquid oxidants to the saturated and vadose zone, there is the potential to release contamination to the groundwater as the oxidant consumes organic matter in the soil. This is dependent on the permittivity of the soil (Interstate Technology and Regulatory Council, 2005). The greater the permittivity, the greater chance for the release of contaminants to the groundwater because the oxidant may not have had enough time to react with the contaminants (Interstate Technology and Regulatory Council, 2005). Table 1 outlines the specifications for site compatibility with each of the commonly used oxidants. Along with these specifications, the soil porosity, free product, and iron content should be evaluated. Free product must not be present because they limit the success of the oxidant. Iron and other heavy metals should be accounted for in the groundwater because they can interfere with the movement of the groundwater during remediation process (decrease in hydraulic conductivity). 

 

Figure 5

Table 1: Considerations for In Situ Treatment with ISCO (Interstate Technology and Regulatory Council, 2005)

 

As shown in Table 1, different oxidants are preferable for certain dominant characteristics of the soil. While these are all comparable for vadose zone treatment, they have different potential negative impacts as well as different levels of persistence.

Each of the previously mentioned processes have particular characteristics which could make them appropriate or not to use in a specific site cleanup. The appropriate process must be decided as product of site characterization (Table1) and investigation of the contaminants needing remediation (Table 2). The persistence of the oxidant in the subsurface is a crucial component because this affects the contact time for advective and diffusive transport and therefore the ability for the oxidant to oxidize the targeted components of the site subsurface being investigated (Huling & Pivetz, 2006).

Figure 6

Table 2: Characteristics of major ISCO processes (Watts & Teel, 2006)

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