In Situ Thermal Desorption at Rocky Mountain Arsenal Hex Pit Denver, Adams County, Colorado

Site Name:

Rocky Mountain Arsenal

Location:

Denver, Adams County, Colorado

Period of
Operation:

October 2001 to March 2002

Cleanup
Type:

Full-scale

Technology:
In Situ Thermal Desorption (ISTD)
- The system design involved a total of 266 thermal wells (210 H-O wells and 56 H-V wells), installed to depths of 12.5 ft below ground surface in a hexagonal arrangement covering an area of 7,194 ft2
- Dewatering wells were installed several feet below the ISTD thermal well field
- Each thermal well was equipped with an electrical heating element designed to reach maximum temperatures between 1,400 and 1,600 degrees Fahrenheit
- A vacuum pressure of approximately 20 inches of water column was maintained along the boundaries of the treatment area to capture steam and contaminant vapors
- The captured off-gas was conveyed to an off-gas treatment system that consisted of a cyclone separator, a flameless thermal oxidizer, a heat exchanger, a knock-out pot, two acid gas dry scrubbers, two activated carbon adsorption beds, and two main process blowers

Cleanup Authority:
CERCLA - Remedial Action
Record of Decision issued in June 1996

Technology evaluated under the U.S. Environmental Protection Agency (EPA) Superfund Innovative Technology Evaluation (SITE) program

Contacts:
EPA Contact:
Kerry Guy
U.S. Environmental Protection Agency Region 8
999 18th Street, Suite 300
Denver, CO 80202-2466
Telephone: (303) 312-7288
E-mail: guy.kerry@epa.gov

EPA SITE Program Contact:
Marta Richards
U.S. Environmental Protection Agency
Office of Research and Development
26 West Martin Luther King Drive
Cincinnati, OH 45268
Telephone: (513) 569-7692
E-mail: richards.marta@epa.gov

Vendor Contact:
Ralph S. Baker, Ph.D.
TerraTherm, Inc.
356 Broad Street
Fitchburg, MA 01420
Telephone: (978) 343-0300
E-mail: rbaker@terratherm.com

Contaminants:
Organic pesticides and herbicides (hex, aldrin, chlordane, dieldrin, endrin, and isodrin)

Composite soil sample contained the following mean pretreatment contaminant concentrations (expressed in milligrams/kilogram [mg/kg]): hex, 7,600; dieldrin, 3,100; total chlordane, 670; endrin, < 280; isodrin, < 200; and aldrin, < 170.

Waste Source:
Disposal of distillation products and other residues that were primarily generated during the production of hex, a chemical formerly used in pesticide manufacturing. The waste was disposed in an unlined earthen pit.

Type/Quantity of Media Treated:
Soil
- The volume of waste in the pit was approximately 3,200 cy, and the waste included solid and semisolid layers of tar-like material
- The contaminated portion of the pit extended over an area of approximately 7,000 ft2 and its depth varied from 8 to 10 ft

Purpose/Significance of Application:
To evaluate the performance of full-scale application of ISTD to treat soil contaminated with hex and other organochlorine pesticides

Regulatory Requirements/Cleanup Goals:
- Remediation Goal I: meet or exceed the ROD requirement of 90 percent destruction removal efficiency (DRE) for the six contaminant of concerns (COCs) that include hex, aldrin, dieldrin, endrin, isodrin, and chlordane
- Remediation Goal II: reduce the mean concentration of the six COCs below the ROD human health exceedance criteria

The performance of the technology was also evaluated according to a number of secondary objectives.

Results:
- The ISTD system at the Hex Pit operated for 12 days. The system was shutdown because portions of the aboveground piping had been corroded by hydrochloric acid that was generated during heating of the organochlorine contaminants. Shutdown of the system prevented the evaluation of the effectiveness of the technology at this site.
- During operation and post-treatment monitoring, sampling and analysis of air emissions indicated that none of the hourly average air quality standards for off-gas emissions had been exceeded during system operation or during the extended well field cool-down period.

Cost Factors:
The total cost of design and construction of the ISTD system was approximately $1.9 million. Because of the short period of system operation, no operation and maintenance (O&M) costs are available.

Description:
Rocky Mountain Arsenal (RMA) near Denver, Colorado, was established in 1942 as a chemical agent and munitions facility, and was later used in the manufacture of pesticides. The disposal of pesticides in drums that later corroded or ruptured resulted in contamination of soil, surface water, and groundwater at the facility. In 1987, RMA was placed on the National Priorities List. One of the contaminated areas of RMA, the Hex Pit, was an unlined, earthen disposal pit used for the disposal of distillation products that were generated during the production of hex, a chemical formerly used in pesticide manufacturing. In addition, other organochlorine pesticides were disposed of in the pit. The 1996 ROD selected innovative thermal technology for remediation of the Hex Pit. The ROD required the application of specific criteria to evaluate the innovative thermal technology. The criteria included greater than 90 percent DRE for hex, dieldrin, and chlordane, and a cost lower than off-site incineration. Several thermal technologies were evaluated and ISTD was selected as the remedial technology because it could meet the criteria specified in the ROD.

The ISTD system was implemented to treat approximately 3,200 cy of contaminated soil. Installation of the system began in October 2001 and was completed in February 2002. The system design involved a number of H-O wells, H-V extraction wells and dewatering wells. The system was started up on March 3, 2002, and was expected to run for 85 days until the end of May 2002. However, because portions of the aboveground piping became corroded by hydrochloric acid that was generated during heating of the organochlorine contaminants, the system was shut down on March 15, 2002, 12 days after system startup. Following shutdown, the Hex Pit site was buried under approximately 3 ft of imported fill material, and the application was evaluated, and lessons learned noted.

The total cost of design and construction of the ISTD system was approximately $1.9 million. Because of the short period of system operation, no operation and maintenance costs are available.