Technology Status Report: In Situ Flushing - CLU-IN

In Situ Flushing Project Summaries
GWRTAC Case Study Database
of 3 to 5 ft / day. The saturated zone was at a depth of less than 10 ft below the surface. The soil
and groundwater at the site was found to be contaminated with low concentrations of a mixture of
PCE, TCE, and weathered jet fuel (methylated alkanes). The compounds treated were PCE and
aviation fuel at up to 1000 µg / kg and 1000 mg / kg, respectively. PCE in the ground-water was
typically at 10 µg / L. The low concentrations were the result of previous remediations activities
conducted at the site. Fluids were introduced to the target area via an upper well screen and
recovered via a lower well screen located in the same casing. The innovative hydraulic system
both injects a surfactant solution and extracts the ground-water/contaminant/surfactant fluid from a
single borehole. Simultaneous injection to, and extraction from, a common vertical borehole
creates a circulating flow pattern that can be used to capture mobilized contaminants that migrate
vertically. In addition, a total of four monitoring wells (one upgradient, three downgradient) were
installed. Each of the monitoring wells was screened over the top five feet of the saturated zone.
Two piezometers were installed at different depths adjacent to the VCW. The shallow piezometer
had a 2-foot screened section intercepting the seasonal water table; the deep piezometer has a 2foot
screened section coinciding with the bottom 2 feet of the VCW. The demonstration area was
10 feet by 10 feet and the depth to ground water is 15 feet. The Dow Chemical Co., a
manufacturer of surfactants, has formed a partnership with the investigators to promote the
development of this technology. The surfactant used was Dowfax 8390 at a delivered
concentration of 36,000 mg/L (10 times the cmc value (3.8 wt%)). Dowfax 8390 has FDA approval
for use as an indirect food additive. Prior to surfactant delivery a tracer test was performed using
fluorescein and sodium chloride.
The delivery/recovery sequence consisted of the following steps:
Injection of 540 gallons of Dowfax 8390 Solution (36,000 mg/L) at a rate of 1 gpm,
1 hour later, recovery of 40 gallons of surfactant/water solution,
20 hours after surfactant delivery, freshwater cycling.
It was found that due to the high hydraulic conductivity at the site, the extraction rate necessary to
capture the surfactant and solubilized contaminants had to be about 10 to 15 times the injection
rate. Produced fluids were analyzed at intervals to document surfactant mass removal. The
analytical results showed that the surfactant increased the contaminant mass extracted by 40-fold
and 90-fold for the PCE and jet fuel constituents, respectively. The surfactant solution
demonstrated minimal sorption (retardation) and did not precipitate in the subsurface formation.
Mass recovery for the surfactant solution exceeded 95 percent for the demonstration study. PCE
concentration in the effluent was increased by more than two orders of magnitude (from 5 ug/L up
to a high of 800 ug/L); LNAPL constituent concentrations were increased by more than an order of
magnitude (from 10 mg/L up to 974 mg/L).
A portion of the produced fluids were concentrated using micellar-enhanced ultrafiltration and then
disposed of by a licensed contractor. The remainder of the effluent was sent to a carbon treatment
system currently in operation at the site. At present, there are no known plans for further testing of
surfactant systems at the Traverse City site.
Researchers made the following recommendations as a result of this study (See Knox, et al., 1997
for more detail).
Ground-Water Remediation Technologies Analysis Center
Operated by Concurrent Technologies Corporation
Appendix - Page 104 of 164
Copyright GWRTAC 1998
Revision 1
Tuesday, November 17, 1998