Thermal Desorption at the Rocky Flats Environmental Technology Site, Trenches T-3 and T-4, Golden, Colorado

Site Name:

Rocky Flats Environmental Technology Site


Golden, Colorado

Period of

June - August 1996


Full scale


Ronnie Hill
Principal Construction Manager
McLaren-Hart, Inc.
9323 Stockport Place
Charlotte, NC 28273
(704) 587-0003

Vacuum-enhanced low temperature thermal desorption
- IRV-100 system manufactured by McLaren-Hart
- 6 treatment chambers (18 feet long, 8 feet wide and 5 feet high; operating capacity of 5yd3 per chamber)
- Each chamber equipped with 16 propane units
- Energy output of total system (infrared energy) - 1.5 MM Btu/hr
- Vacuum condition in treatment chamber - 500 mm Hg
- Air flow rate - 1,000-3,000 cfm
- Residence time - 5.25 hours
- System throughput - 1 yd3/hour
- Soil temperature - 250°F
- Emissions controls - two dry particulate filters (in series), a condenser, and a granular activated carbon unit

Cleanup Authority:
CERCLA - Removal
- Action Memorandum Date - January 18, 1996

EPA Contact:
Tim Rehder
Rocky Flats Project Coordinator
U.S. EPA Region 8
999 18th Street, Suite 500
Denver, CO 80202-2466
(303) 312- 6293
State Contact:
Steve Gunderson
CDPHE Rocky Flats Cleanup Agreement Coordinator
4300 Cherry Creek Dr. South
Denver, CO 80246-1530
(303) 692- 3367
DOE Contact:
Hopi Salomon
Rocky Mountain Remediation Services, LLC
Rocky Flats Environmental Technology Site
P.O. Box 464
Golden, CO 80402- 0464
(303) 966-2677
Fax: (303) 966-8244

Chlorinated solvents, ketones, and low level radionuclides
- The highest concentrations of VOCs in trench T-3 were TCA at 13,000 mg/kg, acetone at 5,100 mg/kg, methylene chloride at 2,400 mg/kg, and carbon tetrachloride at 700 mg/kg
- The highest concentrations of VOCs in trench T-4 were TCE at 680 mg/kg and acetone at 120 mg/kg
- Subsurface soils contaminated with low levels of radionuclides including uranium, plutonium, and tritium

Waste Source:
Burial of drums and debris in trenches on the site

Type/Quantity of Media Treated:
Soil and debris - 3,796 cubic yards
- Soils consist of sandy and clayey gravel
- Moisture content approximately 8%

Purpose/Significance of Application:
Application of thermal desorption to treat soils contaminated with VOCs and low levels of radiation

Regulatory Requirements/Cleanup Goals:
Cleanup goals specified for 12 VOCs:
- Goal of 6 mg/kg each for TCE, TCA, PCE, DCE, DCA, chloroform, carbon tetrachloride
- Goal of 10 mg/kg each for benzene, ethylbenzene, toluene
- Goal of 160 mg/kg for acetone and 30 mg/kg for methylene chloride

- A total of 58 batches (3,796 yd3 total) of soil were treated during this application
- Of the 58 batches treated, 52 met the cleanup goals on the first pass, including 20 batches where all 12 VOCs were below the detection level
- Six batches did not meet the cleanup goals on the first pass, exceeding the level for PCE. These batches were retreated and met the cleanup goals
- Concentrations of six VOCs (TCA, DCE, DCA, carbon tetrachloride, chloroform, and ethylbenzene) were below the detection level in all 58 batches
- According to the vendor, there were no exceedances of the applicable air emissions standards

Cost Factors:
The total cost for this project was $1,934,203, including $1,328,600 in costs directly associated with the thermal treatment.
- The calculated unit cost was $350/yd3 based on the treatment of the 3,796 yd3 of contaminated soil and debris
- The original contract cost was $1,200,000, based on treating 2,200 yds3 of contaminated soil. Two change orders were issued for the remediation of additional soil volumes, changing the total amount of soil treated from 2,200 yd3 to 3,796 yd3, with a final project cost of $1,934,204.

From 1951 to 1989, the U.S. Department of Energy (DOE) used the Rocky Flats site to process and store plutonium, manufacture components for nuclear weapons, fabricate, machine, and assemble components from metals, and store solvents used in the manufacturing processes. Hazardous and radioactive wastes were stored and disposed of at various locations at the site, including on-site trenches. Waste handling practices at the site also included recycling of hazardous materials. Trenches T-3 and T-4 were used for the disposal of sanitary sewage sludge contaminated with uranium and plutonium and miscellaneous debris, primarily flattened drums contaminated with volatile organic compounds (VOCs), uranium, and plutonium. Subsurface soils in trenches T-3 and T-4 were found to contain elevated levels of VOCs, semivolatile organic compounds, and metals, along with low-level radiological contamination. A Proposed Action Memorandum (PAM) was issued in January 1996 calling for thermal treatment of the T3/T4 soils. Prior to treatment, each load of excavated soil was screened using a Field Instrument for the Detection of Low Energy Radiation (FIDLER) to identify "potentially radiologically contaminated material". Soil with readings above 5,000 counts per minute (cpm) was segregated and treated separately from the soil that was not considered to be potentially radioactive. A total of about 380 cubic yards of soil were identified as potentially radioactive.

The thermal desorber used at this site, an infrared radiation-heated unit manufactured by McLaren-Hart (the IRV-100 system), was a modular, batch- operated vacuum system, equipped with six treatment chambers. The system was operated under a vacuum of approximately 500 mm Hg and soil was heated to temperatures of 250°F. Thermal treatment operations were conducted from June to August, 1996. A total of 58 batches (3,796 yd3 total) of soil were treated during this application. Fifty-two of the batches met the cleanup goals on the first pass. The six batches that did not meet the cleanup goals were retreated and met the cleanup goals. The total project cost was $1.9 million with the cost for the thermal treatment application being $1.3 million or $350/yd3 (based on 3,796 yd3 of contaminated soil and debris). According to vendor, the total project cost would likely be less for a similar application at sites where radiological engineering controls were not required.