- Stockpiled soil was treated in 85 yd3 batches using solvent extraction in specially-constructed lined treatment cells.
- The system was operated in a fill-and-drain mode, with 1 day/treatment cycle and 8 treatment cycles/batch.
- The solvent was reclaimed on site through a molecular sieve, and burned on site after the treatment was completed.
- Solvent extraction was chosen over thermal desorption and soil washing on the basis of cost-effectiveness and the relative logistics of mobilizing treatment equipment to the isolated site.
Air Force Installation Restoration Program. The cleanup was negotiated by the Alaska Department of Environmental Conservation (ADEC) and target levels were agreed upon mutually by the Air Force and ADEC.
|Regulatory Point of Contact:|
State of Alaska Department of Environmental Conservation
Contaminated Sites Remediation Program
555 Cordova Street
Anchorage, AK 99501
Bernard T. Gagnon
U.S. Army Corps of Engineers, Alaska District
P.O. Box 898
Anchorage, AK 99506-0898
Air Force Project Manager
Elmendorf Air Force Base, AK 99506
Semivolatile (halogenated) - PCBs. PCB concentrations in untreated soil analyzed during the treatability study ranged from 13 to 346 mg/kg, with an average concentration of 80 mg/kg.
Transformer storage, transformer maintenance, and drum storage
Type/Quantity of Media Treated:
- 288 yd3
- Gravel with fines and likely little or no clay
- Moisture content 9%
Purpose/Significance of Application:
Application of an innovative technology to treat PCB-contaminated soil at a remote site in Alaska.
Regulatory Requirements/Cleanup Goals:
A target cleanup level of 15 mg/kg for PCBs in soil was established for this application.
The contractor was required to perform sampling of the soil at the surface and the bottom of each treatment cell.
Concentrations of PCBs in the reclaimed solvent were required to be less than 2 mg/L before the solvent could be burned on site.
Average concentrations of PCBs were reduced from 80 mg/kg in the untreated soil to 3.27 mg/kg after treatment.
- Concentrations of PCBs measured in samples from the tops and bottoms of each of the five batches of treated soil were reduced to below the 15 mg/kg target cleanup level.
- The concentrations of PCBs in treated soil varied among the batches by one order of magnitude. This variation was attributed to the variations in the concentrations of PCBs in the untreated soil.
- PCBs were not detected at concentrations above detection limits (0.1 mg/L) in the reclaimed solvent.
- Based on a mass balance, approximately 33.8 pounds of PCBs were transferred from the 441,000 kg of contaminated soil to 4,772 pounds of molecular sieve (used to reclaim the solvent), resulting in a contaminated material mass reduction of almost 100 to 1.
- The total cost of this application was $828,179, including $602,530 for mobilization and demobilization, and $225,649 for the solvent extraction. This was less than one-half of the estimated cost of $1,908,545 to transfer all of the contaminated soil to the Defense Reutilization Marketing Office.
- The cost for solvent extraction corresponds to a unit cost of $780 per cubic yard of soil treated.
- Because of its remote location, the site was only accessible by air. Therefore, transportation costs for both mobilization and demobilization were a major factor in the overall cost of the project.
The Sparrevohn LRRS was constructed in 1952, and is one of ten Aircraft Control and Warning sites constructed as part of the air defense system in Alaska. The site is located approximately 200 miles west of Anchorage and is accessible only by air. It is currently operated by the Air Force as a Minimally Attended Radar facility and consists of a lower camp (elevation 1,700 feet) that includes support facilities and an upper camp (elevation 3,300 feet that houses radar equipment.
In 1986, PCB contamination was delineated at the site. In 1989, approximately 450 tons of PCB-contaminated soil from the lower camp were excavated and transported off site for disposal, and approximately 600 tons of PCB-contaminated soil from the upper camp were transported to the lower camp and stockpiled.
A treatability study was conducted on the stockpiled soil in 1995, and as a result of the study, the stockpiled soil was treated in batches using solvent extraction between June and August of 1996. Closure and site restoration activities at the site were completed in September 1996.