Technology Status Report: In Situ Flushing - CLU-IN

In Situ Flushing Project Summaries
GWRTAC Case Study Database
nonyI-phenol ethoxylate, and I percent phosphate ester of nonylphenoI ethoxylate was pumped
through the 3-meter-thick contaminated section of the cell to evaluate surfactant-enhanced
remediation."
"The surfactant was injected in five wells on one side of the cell and extracted from five wells on
the other side. The wells were screened over the entire contaminated zone, which was kept
saturated throughout the experiment. The concentration of tetrachloroethylene (PCE) in the
effluent increased from its aqueous solubility of about 150 parts per million (ppm) to over 4,000
ppm when the surfactant was added. The increase in concentration illustrates the efficiency of the
surfactant process. The surfactant solution used provides a solubility of PCE of about 12,000 ppm;
values in excess of 11,500 ppm were observed in several sampling points on the five multilevel
monitoring wells in the cell. This illustrates that the surfactants provided the same soIubilization
power in the field as predicted in the laboratory."
"The system performed as expected, solubilization was high, surfactant breakthrough was
indistinguishable from that of a conservative tracer indicating sorption was veny low (the aquifer
has no significant clay or organic content) and the air stripper separation was effective. Several
modifications had to be made to the air stripper, however, to prevent foaming; very low air
velocities were eventually employed."
The DNAPL concentration was rapidly reduced in the cell in areas of high hydraulic conductivity.
The residual PCE in the top 1 m was reduced from an initial value of 10% to a value of 1% after
14.4 PVs. At a depth of 2.5 to 3 m, where the ground was either saturated or at 20% saturation
with PCE initially, the PCE saturation was reduced to 3% after 14.4 PVs. Approximately 80% of
the total material was recovered, with the remaining material lost to volatilization or remaining in
dead zones within the formation. The surfactant solution was initially injected into the wells with a
constant-head system on each well; this later was changed to peristaltic pumps due to plugging of
the injection wells.
"The concentration of PCE in the multilevels dropped to a few ppm within 14 pore volumes, except
for the multilevel ports right on the aquitard. These data indicated that the DNAPL had been
removed over nearly the entire aquifer. This was confirmed by analysis of cores taken prior to the
start of the experiment, after seven pore volumes had been circulated, and after 14 pore volumes
had been circulated. These analyses showed that:
I. Nearly all the PCE was removed by 14 pore volumes.
2.The layers of high PCE concentration, which represent perched lenses of PCE, remained at the
same height throughout the experiment indicating the lenses did not drop due to vertical
mobiIization.
3.The persistence of PCE along the aquitard indicates that complete removal would require an
extended treatment time.
After having circulated almost 20 pore volumes of solution, and elevated concentrations of PCE
still occurred in the multilevel at the top of the aquitard.
The base of the aquifer has slightly dipping layers of sand and silt. The PCE is apparently
Ground-Water Remediation Technologies Analysis Center
Operated by Concurrent Technologies Corporation
Appendix - Page 5 of 164
Copyright GWRTAC 1998
Revision 1
Tuesday, November 17, 1998