Technology Status Report: In Situ Flushing - CLU-IN

In Situ Flushing Project Summaries
GWRTAC Case Study Database
contaminants and assessing contaminant biodegradation and toxicity. Soil biotreatability was also
verified and validated. The goal of the on-site demonstration was to evaluate the effects of
surfactants and washing on biological activity, to assess and optimize the well points in controlling
the treatment, and to assess the effect of nutrients and other environmental factors on biological
activity.
Laboratory Results
Using an experimental computer-designed multifactorial plan, the lab studies optimized the
selection of surfactants as a function of the percentage of hydrocarbons extracted. The results
were used to formulate a mixture of surfactanats with no mutagenic effect on E. Coli. Also, the soil
contains a microbial flora that is able to biodegrade contaminants marked with heterotrophic cell
counts on the order of 106 bacteria/gm. Of this number, about 6% of the microorganisms are
BTEX degraders. Respiratory activity in the soil indicates that it is biologically very active. Onecolumn
soil assays identified a condition conducive to a significant 25% reduction in MOG over a
30-day period.
Washing Test Results
Varying conditions of soil saturation were experimented. The distribution of solutions thorugh the
network of well points, with no surface infiltration, provided better hydraulic control of the injected
solutions. Low surfactant concentrations were nonetheless measured outside the site and in the
rock below the experimental plot of land. In a general sense, surfactant showed low efficiency in
extracting hydrocarbons. It appears that the complexity of the geological conditions of the site
influenced these results. Washing with surfactants had little or no effect on either the toxicity of the
soil or groundwater. Moreover, following the washing, mean concentrations of heterotrophic and
specific bacteria were equivalent to those obtained prior to washing, except in groundwater, where
a sproradic increase was noted. Lastly, a reduction or absence of effect on respiration and on
hexadecane mineralization was observed.
Tracer Test Results
A tracer test was done after the washing tests, but before the biological phase, so as to ensure that
the injected solutions were distributed throughout the lot. Horizontal and vertical distribution were
shown to be almost total. Only one characterized zone, possibly containing silt heterogeneities,
was not reached. The vertical migration of the injected solution was generally limited to the
experimental lot. Low concentrations were measured in rock.
Biodegradation Test Results
Oxygen consumption, measured by an in situ respirometric test, varied from 0.1% per hour to 5.1%
per hour. Using a kinetic rate of zero, an estimate of the hydrocarbon degradation rate was
obtained, which, at best, was 137 mg/kg-j. Analysis of gaseous oxygen in the soil pointed out the
unequal distribution of oxygen during aeration: certain zones, possibly containing silt
heterogeneities, remained anaerobic. The vertical and horizontal migration of nutrients is not
limited to the experimental plot of land. Concentrations of NO3- and NH4+ were measured in
unsolidated deposits and in rock off the site.
Ground-Water Remediation Technologies Analysis Center
Operated by Concurrent Technologies Corporation
Appendix - Page 76 of 164
Copyright GWRTAC 1998
Revision 1
Tuesday, November 17, 1998