Technology Status Report: In Situ Flushing - CLU-IN

2.0 IN SITU FLUSHING SUMMARY
2.1 In Situ Flushing Definition / GWRTAC Report Availability
In situ flushing is defined as the injection or infiltration of an aqueous solution into a zone of contaminated
soil/groundwater, followed by downgradient extraction of groundwater and elutriate (flushing solution
mixed with the contaminants) and aboveground treatment and discharge or re-injection. Figure 1 is a
schematic which illustrates a generalized in situ flushing process at a dense, non-aqueous phase liquid
(DNAPL) contaminated site where a flushing solution is being injected into an unconfined aquifer.
Additional information on “In Situ Flushing” may be found in a GWRTAC Technology Overview “O”-Series
Report by the same title, (TO-97-02), and a Technology Evaluation “E”-Series Report (TE-96-02) entitled
“Surfactants/Co-Solvents”. In addition, two Technology Status “S”-Series Reports (EPA 542-K-94-003
entitled “Surfactants”) and (EPA 542-K-94-006 entitled “Co-Solvents”) were prepared by the U.S.
Environmental Protection Agency (EPA) on the subject on in situ flushing, however, this information has
been updated for this status report. A Featured Technology Summary Report for in situ flushing was also
prepared based on the GWRTAC database as of August 7, 1998, however this information has also been
further updated for this status report. All of these reports are available for downloading in *.PDF format
from the GWRTAC website at http://www.gwrtac.org.
2.2 GWRTAC Database / Scale and Status of Projects
Currently, GWRTAC’s case study database contains a total of 84 in situ flushing projects. It should be
noted that by the above definition, GWRTAC has included case studies where plain water (usually treated
groundwater) is used as the flushing solution. Undoubtedly, with this inclusion, hundreds of projects in
which re-injection of treated groundwater occurs as an alternative to NPDES or POTW disposal routes
would also be considered in situ flushing projects in the strictest sense. For the most part, these projects
are not included in the database as in situ flushing remediation studies; the projects included have
identified the flushing action of water or other flushing solution as an integral part of the cleanup process
rather than as a disposition method. GWRTAC is including plain water flushing solutions as in situ flusing
cases, following the convention previously established by U.S. EPA.
Table 1 provides a summary of pertinent information for the in situ flushing case studies which are
currently part of the GWRTAC database. The case studies are listed in alphabetical order by project
name, (which often indicates project location and/or site owner). Also listed for each site is a unique
identification number assigned by GWRTAC; for reasons involved in development of the database, the
GWRTAC ID numbers are not in consecutive order, and there may be gaps in the sequence. It should be
noted that where several individual but unique pilot-scale demonstrations are planned or have occurred at
the same location (ie., Dover Air Force Base, Dover, Delaware; Hill Air Force Base, Layton, Utah), these
individual efforts are counted as separate pilot-scale case studies. However, for laboratory studies, a
given laboratory research group is typically listed only once as a case study, although many different
related efforts may have been conducted by that research group. Table 1 lists not only the GWRTAC ID
and project name and location, but also lists selected primary organization points of contact for the
categories of 1) Potentially Responsible Party (PRP)/Site Owner; 2) Funding Source/Sponsor; 3)
Regulatory Agency; and 4) Technical Team Member. GWRTAC’s actual database contains additional
contacts as available in each category, including names, addresses and phone numbers for all points of
contact. This information is available upon request from GWRTAC. Table 1 also includes information on
the project scale, contaminants addressed, target media, flushing solution used, and the project status. It
may be useful for the reader to refer to Table 1 while reviewing the remainder of this report.
In most cases, although supporting laboratory studies have taken place prior to pilot- or full-scale
demonstrations, or pilot-scale tests may have been conducted prior to full-scale remediation, only the
“most advanced” scale of the project is included in the GWRTAC case study database. That is, if a pilotscale
demonstration is listed, the supporting laboratory studies for the project are not separately listed as
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