The International Information Center for Geotechnical Engineers

Vitrification

Case Study II

  • Parsons Chemical /ETM Enterprises Superfund Site (USEPA, 1997c)

The Parsons site is a former agricultural chemicals mixing, manufacturing, and packaging facility. Soils and sediments at the Parsons site were contaminated with pesticides, heavy metals, and dioxins. The site was occupied by Parsons for approximately 34 years, from April 1945 until 1979. 

Figure 9. Site Location

Parsons_site.jpg

In 1979 and 1980 the Michigan Department of Natural Resources (MDNR) colleted sediment samples from the unnamed creek and a ditch located on the north boundary of the site. Elevated levels of lead, mercury, arsenic, and pesticides, including dichloro-di-phenyl-trichloroethane (DDT) and chlordane were detected in the samples. An action memorandum, dated September 21, 1990, was approved by EPA to conduct a removal action at the Parsons site. Several options were considered for cleanup of the Parsons site, including ISV, incineration, and stabilization. ISV was selected as the remedy because this technology was determined to be capable of reducing volume by 20 to 30%, decreasing the toxicity to near zero, and permanently immobilizing the hazardous substances on the sites. 

The ISV process involved excavating a treatment trench and then constructing melt cells in that trench. The contaminated soil was then excavated and consolidated into the melt cells in the treatement trench. The contaminated soil was then treated, in the treatment trench, via a series of application of ISV. A total of eight melts were conducted to remediate the 5400 tons of contaminated soil. The cell walls were built using concrete, cobble, and particle board as shown in Figure 10.

Figure 10. Side View of Typical ISV Treatment Cell

 

SITE_CELLS.jpg

 Each melt cell was 16 ft deep and 26 ft * 26 ft square. 

 

The ISV Technology operates by means of four graphite electrodes, arranged in a square and inserted a short distance into the soil the treated. A schematic of the Geosafe process is shown in Figure 11.

Figure 11. Geosafe in situ vitrification process (USEPA, 1995b)

 

Geosafe_Process.jpg

The vitrification process used threaded graphite electrodes with an outside diameter of 12 in. supplied in 6-ft sections, and spaced up to 18 ft apart in a square array. These were supported using an electrode feed system, which allowed the electrodes to sink into the melt as the vitrification process proceeded. A treatment rate of 4 to 6 tons of soil per hour was attained, with the vitrified zone growing downward at a rate of 1 to 2 in./h (USEPA, 1995b). 

These melts were conducted over approximately a one-year period, with the duration of each melt ranging from 10 to 19.5 days and the electrical power consumed for each melt ranging from 559,200 to 1,100,000 kWh (USEPA, 1995a).

The application of ISV at the Parsons site succeeded in reducing contamination to below acceptable levels. Monitoring of off-gas emissions during the application of the ISV process revealed that emissions of contaminants in the stack gas were well below applicable regulations. Further, the ISV process succeeded in reducing the volume of contaminated soil by 30% (USEPA, 1997c).

The total cost for the ISV treatment at the Parsons site was $1,763,000 with $800,000 going directly to vitrification operations. This results in vitrification costs of $270 per cubic yard. It is notable that pretreatment cost was pretty high in this case, due to the need to excavate and stage the contaminated soil prior to treatment.

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