Technology Status Report: In Situ Flushing - CLU-IN

In Situ Flushing Project Summaries
GWRTAC Case Study Database
by thick clay deposits that form a capillary barrier to DNAPL migration. The hydraulic conductivity
of this alluvium is in the range of 10-2 to 10-3 cm/s. This aquifer contains tens of thousands of
gallons of DNAPL, seventy percent of which is TCE.
Based on extensive laboratory testing, a chemical system including sodium dihexyl sulfosuccinate
(8 wt%), isopropyl alcohol (8 wt%) and sodium chloride was selected for the field study. Laboratory
work indicates that this system generates a micellar solution that can effectively carry 600,000 mg
of TCE per liter and reduces interfacial tension by approximately two orders of magnitude.
Laboratory work also was conducted to select tracers to be used in Partitioning Interwell Tracer
Tests (PITTs), which were conducted prior to Phase I chemical delivery (May), prior to Phase II
chemical delivery (August), and after Phase II delivery.
A demonstration area was developed during the Spring of 1996 by installing a set of three injection
wells (SB-2, SB-3 and SB-4) and three extraction wells (U2-1, SB-1 and SB-5) in a 3 x 3 line-drive
geometry. This well field also contained one hydraulic control (injection) well (SB-8) to prevent the
upgradient flow of tracers and surfactant, and one interwell monitor well. The distance between
injectors and extractors was 20 ft; the distance between individual injectors and individual
extractors was 10 ft; the water table depth was approximately 25 ft below ground surface; and there
was a 4-ft thick zone of free-phase and residual DNAPL approximately 45 ft below ground surface.
The screened intervals of the injectors and extractors were completed in this DNAPL zone and
extended some distance above it. Prior to the demonstration, about 500 gallons of free-phase
DNAPL were pumped from the recently-installed well field and sent for incineration,
The demonstration was conducted in two phases. The first of these phases comprised a
partitioning interwell tracer test (PITT) followed by a DNAPL solubilization test, both of which were
conducted in May and early June 1996. The PITT determined the spatial distribution and volume
of DNAPL in the test zone of the alluvial aquifer. The solubilization test verified the efficiency of
the selected surfactant, determined if the surfactant would cause the deflocculation and
mobilization of fine-grained particles resulting in a reduction in permeability of the aquifer, and also
addressed the issue of the effect of the surfactant-rich effluent on the efficiency of the steam
stripping system at the site. This test involved the injection of an 8% surfactant solution into one
injection well at 2 gpm for 0.6 days, producing an interfacial tension of 0.1 dynes/cm between the
surfactant solution and the OU2 DNAPL.
"Preliminary evaluations of the chemical delivery/recovery systems and the delivery sequence
were conducted using the numerical model UTCHEM. UTCHEM is described in detail by Delshad,
et al. (1996).
Overall, the field demonstration involved the following sequence of fluid delivery and recovery:
Phase I PreTest Waterflood (1.4 PV)
Initial Partitioning Interwell Tracer Test (4.3 PV)
Phase I Chemical Delivery (0.4 PV SB-2 Only) Phase 1 Water Flushing (3.2 PV)
Phase I Post-Test Recovery Only (2.9 PV)
Ground-Water Remediation Technologies Analysis Center
Operated by Concurrent Technologies Corporation
Appendix - Page 42 of 164
Copyright GWRTAC 1998
Revision 1
Tuesday, November 17, 1998