Formatted Title
New Technology Proves Effective at Quickly and Economically Abiotically Converting Recalcitrant Chlorinated Pesticides to Nontoxic Byproducts
Background/Objectives
A redevelopment housing project tasked with the construction of over 300 single family homes found itself in need of a technology that could quickly remediate building sites impacted with chlorinated pesticides historically applied to control termites. The scope was to excavate the foundation/dripline areas and stockpile those soils for subsequent sampling. 15,612 cubic yards were excavated, and roughly 6,244 cubic yards exceeded critical PCLs, requiring treatment. Of the 6,244 cubic yards above the residential PCL, some would have passed TCLP allowing it to be taken to a nearby Class II LF, but the rest would have likely required disposal as hazardous waste. The alternative of landfilling at a facility over 200 miles distant was grossly expensive and would produce an exponential carbon footprint when considering the effluent of exhaust by heavy duty diesel truck engines. Added complications included the fact that the remediation phase had to be completed on schedule so as not to interfere with the pace of home building. Considering the evolution of chlorinated hydrocarbon remediation at the time, excavation appeared to be the only option. However, such was not the case.
Approach/Activities
Technology had been developed, proven (by field applications), and patented that caused organochlorides to immediately chemically convert to the nontoxic byproducts of carbon dioxide and chloride ion as they came in contact with the chemical reagent. In situ, while aggressively destroying the chlorinated pesticides, the reactions did not create heat and were not reactive with human skin or tissue. Thus, the safety of the technology was assured and had also been proven under field applications. This technology is referred to as Nucleophilic Substitution (SN).
In classical chemistry terms, the SN mechanisms are reduction reactions (not oxidation reactions) as is popularly thought, and the active species is the hydroxide ion (OH-) not the hydroxyl radical [OH]• as is the case with oxidation reactions. The SN reaction rate depends upon the concentration of the substrate and the concentration of the nucleophile (hydroxide ion) (OH-). Environmentally, in the treatment of halogenated contaminants, this mechanism circumvents the chemical oxidation mechanisms and thus, obviates the need for consideration of the effect of oxygen demand from soil oxygen demand (SOD) or natural oxygen demand (NOM) sources. The reaction involves the production of a carbonium cation (R-C+) intermediate and is commonly seen in reactions of secondary or tertiary alkyl halides under basic conditions. With primary alkyl halides (chlorinated solvents or chloro-alkyl compounds), the reaction byproducts are commonly carbon dioxide and chloride ion.
Results/Lessons Learned
Based on the work conducted at the Site, WSP and DeepEarth Technologies, Inc. have demonstrated the effectiveness of the treatment at significantly reducing concentrations of organochlorine pesticides in soils. To date, organochlorine pesticide impacted soils have been successfully treated in-situ to below Site critical PCLs at 79 of 89 treated former residence locations. Four former residence locations were successfully re-treated to below critical PCLs at a designated Soil Management Area and roughly 6,244 cubic yards of impacted soil excavated from a separate area have been treated to below critical PCLs. The assessment and treatment activities at the Site have resulted in significant savings compared with excavation and disposal of impacted soils that may be classified as hazardous or Class 1 or 2 non-hazardous waste at an off-site facility. The findings from our current work will lead to a significant increase in efficiency and cost effectiveness when WSP and DeepEarth Technologies, Inc. begin a similar scope of work for the client at an adjacent site at the beginning of 2024.