Environmental Engineering Reference
In-Depth Information
Table 5.2
Core Sample Locations for Direct Molecular Analysis (16S and PLFA)
1-Year
Posttest Core
(1999)
2-Year
Posttest Core
(2000)
Pretest Core
(1998)
Location
DNAPL target area,
between RW-6 and RW-7
C6
C10, C19
C36
Background, near MW-2
C5
C11
C35
Upgradient, well C7
C7
C20
C37
Downgradient, well C1
C1
C16, C17, C18
C31
Downgradient, well C2
C2
C14
C32
Downgradient, well C3
C3
C15
C33
Downgradient, well C4
C4
C12, C13
C34
with plastic caps. Materials used to handle these cores were sterilized with
isopropyl alcohol between core sections. Cores were immersed in a liquid
nitrogen canister for 5 min and stored frozen until analysis. A compilation
of the core locations and times of collection is given in Table 5.2.
5.4.2.3 Cosolvent flush and partitioning tracer tests
The pilot-scale field test of
in situ
alcohol flushing was conducted in August
1998 as described by Jawitz et al. (2000). The alcohol flushing began on
August 9, 1998, and ended on August 15, 1998. The injection/extraction
system was designed so that the IWs were screened deeper than the RWs to
promote an upward flow of the injected fluids. The configuration of injec-
tion/extraction wells was selected based on numerical model simulations
conducted by Sillan (1999). A total flow of 15.1 l/min was distributed equally
to the three IWs. The interior recovery wells (RW-3, RW-4, RW-6, and RW-7)
had extraction rates of 5.9 l/min, and the outer two wells (RW-2 and RW-5)
had extraction rates of 3.4 l/min, which resulted in a 2:1 extraction-to-injec-
tion ratio. Steady-state flow was maintained so that the water table position
remained constant during the tests. The test zone was flushed with 34 kl
(equivalent to 2 pore volumes) of a 95% ethanol/5% water mixture over the
3-day period. In the initial 10 hours the ethanol concentration was ramped
from 0 to 95% to minimize density problems. Posttest hydraulic containment
began on August 15, 1998, and continued until August 25, 1998, after the
ethanol concentration in the treatment system influent dropped below the
10,000 mg/l termination criterion (LFR Levine Fricke, 1998).
A partitioning tracer test conducted prior to the alcohol flushing was
used to estimate approximately 68 l of PCE in the zone swept by the injec-
tion/recovery well system (Jawitz et al., 2000). A postflushing partitioning
tracer test indicated that approximately 26 l of PCE remained in the swept
zone, so approximately 42 l of PCE was removed during the cosolvent flush.
A more detailed description of the tracers used and data evaluation is given
in Jawitz et al. (2000).
