Thermal Desorption at the Rocky Flats Environmental Technology Site, Golden, Colorado

Site Name:

Rocky Flats Environmental Technology Site


Golden, Colorado

Period of

July - August 1997


Full scale


Ron Hill
McLaren Hart
9323 Stockport Place
Charlotte, NC 28273
Phone: (704) 587-0003

Thermal Desorption
- The McLaren Hart IRV-150 Batch Thermal Desorption Unit was used, including four ovens
- Each oven is 8-feet wide by 18-feet long by 1.5-feet high, and includes two removable trays, with a capacity of 2.25 cubic yards of soil per tray
- The desorber was operated at 180oF and a soil residence time of 2.5 - 3.5 hours
- Off-gases were treated with HEPA filtration, condensation, and vapor-phase GAC
- Condensate was treated using chemical precipitation, microfiltration, neutralization, dewatering, ultraviolet/peroxide oxidation, ion exchange, and liquid-phase GAC adsorption

Cleanup Authority:
- DOE Final Action Memorandum 3/97

Site Contacts:
Norma Castaneda
Rocky Flats Field Office
10808 Highway 93, Unit A
Golden, CO 80403
Phone: (303) 966-4226

Tom Greengard
10808 Highway 93, Unit B
Golden, CO 80403
Phone: (303) 966-5635
EPA Contact:
Tim Rehder
U.S. EPA Region 8
999 18th Street, Suite 500
Denver, CO 80202
Phone: (303) 312-6293

Halogenated Volatile Organic Compounds (VOCs)
- Tetrachloroethene (PCE) was the primary VOC, with concentrations as high as 760 mg/kg
- Trichloroethene (TCE), carbon tetrachloride, and methylene chloride were not detected above their cleanup goals in any soil samples

Waste Source:
Burial of drums of waste

Type/Quantity of Media Treated:
- 724.5 cubic yards of soil from two groups: (1) above claystone/sandstone layer; and (2) weathered claystone/sandstone material
- Soil in first group consisted of clay (15-50%), silt (10-40%), sand (20-30%), and gravel (10-40%)
- Soil in second group consisted of clay (45-90%), silt (40-85%), and sand (5-55%)
- Moisture content of both groups ranged from 10-18%

Purpose/Significance of Application:
Thermal desorption of soil contaminated with halogenated volatile organic compounds

Regulatory Requirements/Cleanup Goals:
Cleanup goals for treatment of soil were identified for PCE (6.0 mg/kg), TCE (4.0 mg/kg), carbon tetrachloride (2.0 mg/kg), and methylene chloride (5.77 mg/kg)
- Based upon air dispersion modeling results, stack monitoring for radionuclides was not required

Except for two batches, all treated soil samples met the cleanup goals on the first pass, with all results below detection limits
- The two batches that did not meet the treatment goal for PCE were re-treated met the goals after re-treatment

Cost Factors:
A total of $2,316,000 was expended for cleanup of this site, including $580,000 for planning and site preparation, $210,000 for project management, and $1,526,000 for excavation, treatment, waste disposition, and site restoration. Information about the portion of the $1,526,000 for excavation, treatment, waste disposition, and site restoration that was directly attributable to thermal treatment was not available. Therefore, a unit cost for treatment of contaminated soil was not calculated. DOE considers information about the amount expended for thermal desorption treatment confidential business information.

The U.S. Department of Energy (DOE) used the Rocky Flats Environmental Technology Site (RFETS) to fabricate components for nuclear weapons from 1951 to 1989. Hazardous mixed wastes generated from the associated machining operations were disposed at various locations at the site, including the Mound Site. Approximately 1,400 drums containing hazardous mixed waste, including uranium, beryllium, hydraulic oil, carbon tetrachloride and PCE were placed at the Mound Site between April 1954 and September 1958. These drums were covered with soil thus generating a "mound". Over time, contamination leaked from these drums into the surrounding soils and groundwater.

Thermal desorption technology was selected to treat contaminated soils from the Mound Site. A batch process design was selected based on the relatively small volume of soil to be treated, and a desire to minimize size reduction activities because of the presence of radionuclide contamination. This application included several enhancements to the McLaren Hart thermal treatment system, including use of trays to hold the soil instead of placing the soil directly into the ovens, and use of a preheater in the off gas treatment train between the condenser and the HEPA filters to raise the temperature of the off gas leaving the condenser above its dew point. Treated soil samples met the cleanup goals on the first pass, with results below detection limits for all but two batches. These two batches were re-treated and met the goals after re-treatment. Information was not available about the cost for thermal desorption treatment at this site.