In Situ Chemical Oxidation of Chlorinated Pesticide Soil Impacts

Problem

A former tree farm was purchased for commercial redevelopment. An area of approximately 1/3 acre was found to be impacted with chlorinated pesticides at concentrations up to 65,000 ug/Kg. The site development plan is stalled until the chlorinated impacts have been removed or treated to less than 2.2 mg/Kg for DDT and 0.3 mg/Kg for Dieldrin. Remedial options consisted of; excavation and offsite disposal of all impacted soils (i.e., the top 12 inches of soil are impacted), or on site in situ treatment.

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Solution

Pelorus was contracted to perform in situ chemical oxidation of the surficial soil contamination at the site. A laboratory feasibility test was performed to evaluate various chemical oxidation/reduction reagents. A number of formulations and combinations were evaluated including; Fentons reagent, permanganate, persulfate, and zero valent iron. The most efficient process was chemical oxidation with Fentons Reagent.

Pelorus engineered a landfarming application of hydrogen peroxide and catalysts to achieve chemical oxidation of the target constituents. Because of the hazards associated with the use of high strength hydrogen peroxide in a surface application the project health and safety plan became a critical aspect of project implementation. Workers were outfitted in rubber acid resistant suits, rubber gloves and steel-toed rubber boots. In addition, full faced supplied air respirators were used by field team members working within the exclusion zones.

Catalysts, stabilizers and rate enhancing reagents were applied in solid form and tilled into the soil to a depth of 12 inches. The soil was then irrigated to achieve the pre-defined soil moisture content. Hydrogen peroxide was then applied to the treatment zone using an anhydrous ammonia injector specially modified for compatibility with hydrogen peroxide.

After a single application, 2/3 of the treatment area had been remediated to below the target levels for DDT and Dieldrin. The remaining area has received two additional applications to with DDT below the cleanup standard. Dieldrin on the other hand has reached an asymptotic level averaging 0.5 mg/Kg. The apparent resistance of Dieldrin is a function of the very high organic carbon content of the soil. Therefore, more frequent applications of chemical oxidant will be required to achieve the standard.

To date the client has saved $1.2 million over the excavation and offsite disposal option.

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