Flushing (in situ) -- cyclodextrin-enhanced flushing. (CDEF)
- Flushing system consisted of eight 4-inch PVC injection/extraction wells - five for both injection and extraction and the other three for extraction only. Wells were screened in the lower 5 feet of the surficial aquifer.
- System operated at an average flow rate of 7,200 gallons per day.
- Cyclodextrin solution (20% by weight) was stored in a 6,500 gallon storage tank and gravity fed into the injection/extraction wells.
- Groundwater extraction wells were used to capture the injectate flushed through the contaminated media.
- Extracted groundwater was passed through a 2 µm sand filter to remove fines.
- Filtered groundwater was then passed through an air stripper to remove TCE from the cyclodextrin-TCE complex.
- A pervaporation unit was also used for TCE removal. The unit operated only for a limited period of time to field test it as an alternative to air stripping.
- The stripped cyclodextrin solution was then recycled using an ultrafiltration unit and reinjected
- The gas-phase waste stream from the air stripper was passed through an activated carbon unit prior to atmospheric discharge.
LANTDIV Remedial Project Manager
1510 Gilbert Street
Norfolk, VA 23511-2699
Phone: (757) 322-4792
USEPA Region III Remedial Project Manager
USEPA Region III
Federal Facilities Branch
1650 Arch Street
Philadelphia, PA 19103-2029
Phone: (215) 814-5129
State Remedial Project Manager
Virginia Department of Environmental Quality
629 East Main Street, 4th floor
Richmond, VA 23219
Phone: (804) 698-4227
VOCs - TCE, 1,1,1-TCA, 1,1-DCE, and chloroform
Waste generated from metal plating operations
Type/Quantity of Media Treated:
- Surficial aquifer is composed primarily of poorly sorted sand with lenses of clay, silt, sand, peat, and shell fragments. The aquifer is generally unconfined and is underlain by a clay confining unit.
- Water table was encountered 7 to 8 feet below ground surface.
- Hydraulic conductivity of the aquifer in the remediation zone was 8 x 10-4 centimeters per second.
Purpose/Significance of Application:
Field demonstration of CDEF to recover chlorinated solvent DNAPLs from soil and groundwater.
Regulatory Requirements/Cleanup Goals:
To achieve greater than 90 percent reduction in DNAPL mass and greater than 99 percent reduction in aqueous TCE concentrations.
Mass reduction in subsurface DNAPL was between 70 and 81 percent. This corresponded to a mass of 39 kilograms and a volume of 30 liters. The average TCE concentration in groundwater was reduced by 78 percent.
The total cost of the demonstration was $863,000, consisting of a capital cost of $448,000, and an operation and maintenance cost of $409,000.
Site 11, Naval Amphibious Base Little Creek (NABLC), Virginia Beach, Virginia encompassed a former plating shop that was operated by the NABLC, School of Music. Chlorinated solvents and other industrial liquids that were stored in tanks at this facility leaked and migrated into the underlying surficial aquifer. Impacted soils, tanks and piping were removed in 1996. The site was listed on the NPL on May 10, 1999. The contaminants of concern at this site include chlorinated solvents such as TCE, 1,1,1-TCA, 1,1-DCE and chloroform. A demonstration of CDEF was conducted at the site to evaluate the effectiveness of the technology to treat the contaminants of concern. The demonstration began in June, 2000 and continued until September, 2000. Treatment goals for the demonstration were to achieve greater than 90 percent reduction in DNAPL mass and greater than 99 percent reduction in aqueous TCE concentrations.
CDEF achieved 70 to 81 percent DNAPL mass reduction and approximately 78 percent reduction in the average concentration of TCE in groundwater. The total capital cost for constructing the CDEF system was $448,000, and the total cost of operation and maintenance for the period of the demonstration was $409,000.
Some problems were encountered during the demonstration. One of the problems was that aeration of the injectant caused iron present in the groundwater to precipitate inside the air stripper, increasing the air stripper's maintenance frequency. In addition, injection wells became clogged by the precipitation of iron in the injectant. These problems were solved by storing the injectant in tanks long enough to allow the injectant's natural oxidant demand to consume any dissolved oxygen.