Low Temperature Thermal Desportion
- Patented I.R.V.-100 LTTD system
- 1.2 million BTU/hr system; six carbon steel treatment chambers (5 cubic yards of soil per chamber capacity)
- Each chamber equipped with 16 propane-fired infrared heaters; soil temperature of 600F
- System operated at under a vacuum of 12 to 20 column inches of water; volumetric air flow of 500 to 1,000 cubic feet per minute per chamber
- Residence Time- 60 minutes for clay soils and 120 to 150 minutes for black stained soils
- Off-gas treatment included two cyclones, two air expansion chambers to cool the temperature of the air from about 120 F to about 90F, and one 4,000 pound activated carbon adsorption unit
- Total actual project cost - $5,402,801, including $4,647,632 in actual costs for McLaren/Hart's application of thermal treatment and other project costs identified by USACE for design and project remediation ($192,827), design contract costs ($249,320), and construction contract management ($312,320)
- The unit cost for the application was $220 per cubic yard, based on 13,986 cubic yards of soil treated
- McLaren/Hart's actual costs of $4,647,632 include $2,622,470 for five modifications to the contract
- USACE subsequently paid McLaren/Hart a total of $3,905,256 for the remediation of the K area soils, as a result of a settlement agreement regarding costs of the modifications
The Letterkenny Army Depot is a 19,243-acre U.S. Army facility located in Chambersburg, Franklin County, Pennsylvania. Since 1942, the Army has used the site to overhaul, rebuild, and test missile systems; store and demilitarize ammunition; and maintain and refurbish equipment and vehicles. Operations at the facility have included degreasing, metal plating, painting and paint stripping, steam cleaning, and petroleum storage. Wastes from these operations were disposed of in landfills, trenches, pits, and surface impoundments at the site. Site investigations identified elevated levels of volatile organic compounds in soil and groundwater in the site, including three areas of soil contamination, also referred to as the K areas. K-1 was a waste disposal lagoon, K-2 was used as a transfer station, and K-3 was an area used to store drums of waste solvent. A 1992 remedial investigation identified elevated levels of TCE, polychlorinated biphenyls (PCBs), metals, and semivolatile organic compounds (SVOCs) in soils in the K areas. A Record of Decision, signed in June 1991, specified excavation of VOC-contaminated soil and on-site treatment using low temperature thermal desorption.
A low temperature thermal desorption system (LTTD), model I.R.V.- 100 designed by McLaren/Hart, was used to treat the contaminated soil from the K areas. The 1.2 million BTU/hr system, operated under vacuum, included a total of six carbon steel treatment chambers used to heat soils to temperatures up to 600F. The unit operated from September 1993 to October 1994. A total of 13,986 cubic yards of soil were treated during this application, including 2,620 cubic yards of "black stained" soils that were encountered during the excavation of areas K-1 and K-3. The black stained soils contained heavy oils, greases, and debris and were stockpiled separately from the "clay soils" for treatment. Approximately 10% of the clay soils and 14% of the black stained soils from the K-1 area were retreated. In addition, a total of about 4,000 cubic yards of treated soils was stabilized prior to disposal. This included treated soil that was above the TCLP metals levels and from the top 6 feet of K-1 area and top 3 feet of K-2 area. The remaining treated soil was backfilled on-site.
According to vendor, the presence of the black stained soils had not been anticipated at the time of the original contract. The adverse effects of these soils on the operation of the unit, from the heavy hydrocarbons in the soil, were discovered during the first demonstration test and required modification to the design and operation of the system, including expansion of the emissions controls. This resulted in increased costs and a delay in the schedule over the original plan.