Technology Status Report: In Situ Flushing - CLU-IN

4.0 SUMMARY / ISSUES IDENTIFIED / RESEARCH FOCUS
As noted in the previous sections of this report, the majority of pilot-scale demonstrations of in situ flushing
to date known to GWRTAC have involved the use of surfactants and cosolvents. In the U.S., where fullscale
site remedies have utilized in situ flushing, plain water has typically been used as the flushing
solution. Halogenated VOCs are the most frequently targeted contaminant based on projects of all
scales. Some sources of information to GWRTAC have indicated a reluctance of regulatory personnel to
the use of injectants for site remediation due to toxicity concerns. Research efforts underway at some
institutions are focusing on the development of low toxicity, biodegradable, or U.S. Food and Drug
Administration (FDA)-approved food additive flushing reagents, to address this concern. In addition to
toxicity concerns relative to injectants, persons responsible for implementing or regulating in situ flushing
projects are concerned with containment, since the alteration of hydraulic and chemical properties, if
uncontrolled, could exacerbate the contamination problem at a site. These two are the most likely
technical reasons for the small number of full-scale projects using surfactants, and why many of the
enforcement sites flush within physically contained subsurface zones, such as sites first bound by slurry
walls. Economically, recycling and reuse of surfactants or other flushing additives is also of concern,
especially to site owners or PRPs. At one site in Pennsylvania, although in situ flushing was identified as
accelerating PCB removal from groundwater via a spring outfall from fractured sandstone, in situ flushing
was discontinued after pilot testing largely due to the lack of focus on how to economically treat the
elutriate. Some research projects are specifically addressing recycling and reuse, as well as modeling of
the flushing process. At least one regulatory agency personnel expressed concern that commercially
available models often failed to compensate for the narrow features of slurry walls and infiltration trenches,
and it often can not be proven that all the water being infiltrated can indeed be captured.
Ground-Water Remediation Technologies Analysis Center © GWRTAC
Operated by Concurrent Technologies Corporation Page 8 Revision 1 11/17/98