- Soil was pre-screened using a 1 ½ -inch bar screen.
- Pre-screened soil was fed to the direct-fired, rotary kiln-type thermal desorption unit.
- Soil was treated at nominally 700-750°F with a throughput of 50-150 tons per hour.
- Off-gas was treated with a baghouse and recycled to the desorber or thermally oxidized and discharged to the atmosphere.
Conducted under a federal facilities agreement among the EPA, the U.S. Army, Ft. Lewis, and the State of Washington Department of Ecology
|USACE Point of Contact:|
U.S. Army Corps of Engineers
P.O. Box 3755
Seattle, Washington 98124-2255
|EPA Point of Contact:|
Remedial Project Manager
U.S. EPA, Region 10
Washington Operations Office
300 Desmend Street, Suite 102
Lacey, Washington 98503
Telephone: (360) 753-9014
Semivolatile (nonhalogenated) - polycyclic aromatic hydrocarbons (PAHs). PAHs were detected throughout the SRCPP, with individual PAH concentrations as high as 410 mg/kg, and typically not exceeding 2 mg/kg.
Leaks and spills
Type/Quantity of Media Treated:
- 104,336 tons of soil were treated during this application, including 2,200 tons during the field demonstration.
- Soil was classified as various sand and gravel.
- Moisture content was 4%.
Purpose/Significance of Application:
Thermal desorption of a relatively-large amount of soil contaminated with PAHs.
Regulatory Requirements/Cleanup Goals:
- Cleanup levels for this application were 1 mg/kg for the sum of the concentrations for seven carcinogenic PAHs (based on the Record of Decision) and 200 mg/kg for both diesel range and oil range fuel hydrocarbons (based on the Ft. Lewis base management).
- The PAH cleanup level was derived from Washington State Model Toxics Control Act Method B cleanup levels for ingestion of soil containing carcinogenic PAHs.
- Air emission limits for this application were established by the Puget Sound Air Pollution Control Agency as performance standards limiting the acceptable physical operating parameters for the baghouse and thermal oxidizer.
- The LTTD system used at the SRCPP achieved soil cleanup levels and air emission standards during the treatment of the contaminated soil at a desorber temperature generally between 700 and 750°F.
- During the field demonstration test, the system treated soil contaminated with total carcinogenic PAHs at levels ranging from 0.6 mg/kg to 4.2 mg/kg to less than the 1.0 mg/kg cleanup level established for this application.
- During full operation of the LTTD system, samples of treated soil had concentrations of total carcinogenic PAHs ranging from below detection limit to 0.44 mg/kg.
- The total cost for this application was approximately $7,100,000. The unit cost for thermal desorption treatment of contaminated soil was approximately $34 per ton treated, and for the entire RA was approximately $68 per ton treated.
- The original bid for this application was approximately $3,500,000. There were 23 modifications to the bid, resulting in a final cost that was approximately twice the original. Modifications included such items as an increase in the quantity of soil requiring treatment and additional site work.
The SRCPP occupies approximately 25 acres between Sequalitchew Lake and Hammer Marsh on North Ft. Lewis, approximately 12 miles south of the city of Tacoma, Washington. It was operated from 1974 to 1981 as a production and research facility that worked to develop a solvent extraction process to derive petroleum hydrocarbon products from coal via operations such as heat extraction and thermal cracking. Soil at the SRCPP was contaminated by leaks and spills of process materials that occurred during operations at the plant.
On the basis of the remedial investigation and pre-remediation surface soil chemistry survey, 17 areas were identified for excavation of contaminated soil. The thermal desorption system used to treat the soil consisted of a rotary thermal desorber with a baghouse and a thermal oxidizer for off-gas treatment.
Approximately 104,000 tons of contaminated soil were treated during a field demonstration test and full-scale operation of the system. Samples of treated soil had total concentrations of carcinogenic PAHs ranging from below detection limits to 0.44 mg/kg.