Technology Status Report: In Situ Flushing - CLU-IN

In Situ Flushing Project Summaries
GWRTAC Case Study Database
to as a Waterloo Barrier system. The poorly sorted sand and gravel aquifer is approximately 15 to
20 ft below the surface to the clay aquitard. Four injection and three extraction wells are located on
the opposite 3 m sides of each cell. Well screens are variable from the clay layer to above the
water table. In the interior are 12 evenly spaced sampling wells, each with nested ports at 5
vertical depths. The saturated zone pore volume (PV) within each cell is variable from 1,000 to
2,500 gallons per cell. The hydraulic conductivity of the saturated potion of the upper sand and
gravel unit at OU1 is 10-1 to 10-2 cm/sec based on aquifer test data, and 10-2 to 10-5 cm/sec
based on slug test data. For all of the flushing experiments (those with surfactants, cosolvents,
and cyclodexdrin), the flushing rate will be approximately one pore volume per day. Prior to and
after treatment of each cell, a partitioning tracer test has or will be performed. The mix of tracers
will be designed according to the expected volume of NAPL within the cell before and after
treatment. Among the tracers, hexanol and dimethylpentanol may be included.
For the test at Cell 8, OU 1, conducted in the summer of 1996, a field trial involving flushing with a
microemulsion precursor (a mixture of a nonionic surfactant and alcohol) was conducted. A
mixuture of 3.5 wt% Brij 91 [Polyoxyethylent (10) Oleyl Ether]) and 2.5 wt% n-pentanol was used to
generate a stable, single-phase microemulsion (SPME) of LNAPL in the aqueous solution. In the
single-phase microemulsion SPME process, a surfactant and co-surfactant (alcohol) mixture is
added to the subsurface, where a water-continuous, low-viscosity, oil-in-water microemulsion forms
on contact with residual NAPL. This Winsor Type I microemulsion can be diluted in water and
transported through porous media as a single-phase, low-viscosity fluid. In contrast with micellar
solubilization, which typically requires 10 - 20 pore volumes of flushing and selectively solubilizes
NAPL components, fewer pore volumes of the surfactant/alcohol mixture are needed to
microemulsify all NAPL components uniformly. The SPME study was divided into three separate
phases: Laboratory Precursor Selection, Field Implementation, and Numerical Simulations.
The first phase of this study was to select a surfactant and cosurfactant which together form the
microemulsion precursor, which would produce a low-viscosity, single-phase microemulsion on
contact with the complex, multi-component NAPL found at the field site. Eighty-six surfactants and
a number of alcohols were screened, with enhanced NAPL solubilization and low-viscosity (