Technology Status Report: In Situ Flushing - CLU-IN

In Situ Flushing Project Summaries
GWRTAC Case Study Database
PCE. The surfactant solution was recycled. Phase II was similar with one well being replaced. In
Phase III a new surfactant was used. In Phase IV a smaller area was tested.
Surfactant was added to the extracted groundwater at the surface, injected through an array of
distribution wells, and then removed via extraction wells. The contaminants were separated by air
stripping, and the stripped solution mixed with surfactant. The surfactant solution was then reinjected;
the concentration of surfactant used was 1% in this pilot test. The surfactant was not a
food-grade additive, but is approved for use in "food preparation procedures", has low toxicity, and
is readily biodegradable under both aerobic and anaerobic conditions. The cycle of extraction,
aboveground treatment and mixing of surfactant and re-injection of surfactant was repeated
throughout the test.
The project was conducted in four separate phases. In Phase I (June 1991 to August 1991), a 1%
surfactant solution was delivered through six distribution wells, and removed via one central
extraction well. In Phase II (March 1992 to June 1992) a new extraction well was utilized as one
original extraction well was rendered unusable by sanding. During Phase II, the original surfactant
was subjected to a high sorption rate, and biofouling of surface tanks and delivery wells occurred.
In Phase III (June 1992 to October 1992), because of the issues encountered in Phase II, the
surfactant was changed. In Phase IV (January 1993 to February 1993), a smaller area comprising
the northern half of the original test area was utilized, due to low flow rates due to a depressed
regional water table.
In the first two phases, completed in 6/91-8/91 and 3/92-6/92, respectively, the surfactant was
found to sorb considerably and biofouling of the above ground tanks occurred resulting in the
change of surfactant. The initial concentrations in monitoring wells were 200-300 mgL with
concentrations jumping to 800-900 mg / L at the point that the surfactant reached 0.5% in the
monitoring wells (i.e., about 1 PV). The average concentration of CTET in the solution recovered
was 790 and 219 mg / L for Phases I and II, respectively. After 12.5 pore volumes, a total of 73
gallons of CTET were removed.
Prior to the test, CTET was found at >1,000 ppm in both soil core and water samples from the test
zone. During the in situ flushing test, the average effluent concentration of CTET decreased from
790 ppm (Phase I) to 219 ppm (Phase IV). A total of approximately 73 gallons of CTET was
removed during the project, after injection of 12.5 pore volumes of flushing solution. DNAPL
removal progressed at a rate more rapid than would be expected with standard pump and treat
technology, based on analysis of three monitoring well nests within the DNAPL source area. It was
concluded that although initial capital costs would be greater than pump and treat, the reduction in
time required to complete remediation greatly reduces the O&M costs.
Report(s)/Publication(s) (Additional Information Sources):
Fountain, John; Hodge, D., Project summary: Extraction of organic pollutants using enhanced
surfactant flushing: Initial field tests, Part I, NY State Center for Hazardous Waste Management,
February, 1992.
Fountain, J. C. “A pilot scale test of surfactant enhanced pump and treat, in Proceedings of Air
and Waste Management Association’s 86th Annual Meeting, Denver, Colorado, June 13-18, 1993.
Fountain, J. C.; Waddell-Sheets, C., A pilot field test of surfactant enhanced aquifer remediation:
Ground-Water Remediation Technologies Analysis Center
Operated by Concurrent Technologies Corporation
Appendix - Page 10 of 164
Copyright GWRTAC 1998
Revision 1
Tuesday, November 17, 1998