IN SITU CHEMICAL OXIDATION OF CARBON DISULFIDE IMPACTED SOIL

Between 1996 and 1998, Witco Corporation (now Crompton Corporation), Environmental Resources Management (“ERM”), Fahrenthold & Associates and Terra Constructors successfully developed and implemented an innovative, and now patented, in situ chemical oxidation treatment technique for carbon disulfide (CS2) impacted soils at the Halby Chemical Superfund Site located in Delaware (“Site”). The project involved technology research and development, laboratory and field treatability testing, and full-scale implementation.The literature suggested that chemical oxidation of CS2 might be viable, although industry experience was limited, especially with high concentrations and large soil volumes, and the reaction could be potentially explosive. Nonetheless, in situ chemical oxidation was pursued as a relatively safe, aggressive and cost-effective approach compared to other alternatives. Laboratory treatability testing was performed to evaluate the efficacy of peroxide-based oxidants, including hydrogen peroxide, sodium percarbonate, and sodium perborate. The treatability testing demonstrated that all three peroxidants could provide 99+% CS2 removal; however, sodium percarbonate was selected for field pilot testing based on ease of application, controlled reaction kinetics, reaction byproducts, cost, and treated soil consistency.Two field pilots (Phases I and II) were conducted to verify the results of laboratory testing. Phase I was conducted using a low-pressure direct injection unit, selected as a less intrusive delivery system. The results of the Phase I pilot showed limited CS2 reduction, which was believed to be caused by the system's inability to deliver sufficient oxidant to the entire soil mass. Phase II was conducted using a Single Auger Mixing (SAM) unit, a six-foot diameter crane-mounted soil auger, which was selected as a more aggressive application method. Phase II demonstrated consistent 99+% removal of CS2 under actual field conditions. Based on these results, full-scale treatment using the SAM unit was initiated.Full-scale treatment was completed in approximately 20 weeks. Over 10,000 cubic yards of soil, with up to 16% CS2, were successfully treated to an average CS2 concentration of approximately 200 mg/kg (1/5 the cleanup goal). The treatment operations were completed safely, including over 10,000 man-hours without a health or safety incident. The cost of this project, including development, field treatability testing and full-scale treatment, was an order of magnitude less than excavation/off-site disposal, and approximately 1/2 to 1/3 the cost of other technologies considered.