Environmental Engineering Reference
In-Depth Information
5.4.2.4 Hydrogen gas analysis
In July 1999, hydrogen gas analysis was conducted on groundwater from
selected monitoring wells. Monitoring wells were pumped at a rate of 250
to 300 ml/min through a 250-ml gas sampling bulb containing a gas pocket
of approximately 20 ml volume. A 2-ml gas sample was collected from the
gas pocket with a gas-tight syringe and injected into an RGA3 Reduction
Gas Analyzer. Samples were collected and analyzed over time until equilib-
rium was reached at individual wells.
5.5 Accomplishments
5.5.1 Solvent extraction (SE) pilot test
The cosolvent flushing pilot test activities were completed on September 10,
1998, with the collection of posttest groundwater samples. More detailed
information concerning the cosolvent flushing test and an evaluation of the
partitioning tracer data can be found in Jawitz et al. (2000) and LFR Levine
Fricke (1998).
Enhanced dissolution and solubilization of PCE was demonstrated as
a result of cosolvent flushing. Analytical data from the recovery wells,
except for RW-5, show that the peak PCE concentrations were 3 to 80 times
larger than the initial PCE concentrations (Figure 5.9). According to the
partitioning tracer test, RW-5 showed very low amounts of DNAPL present
in the swept zone, and the precosolvent flush groundwater PCE concen-
tration was 1 mg/l. During the cosolvent flush, the maximum concentration
of PCE in this well was 2 mg/l, with a maximum ethanol concentration of
4% (Figure 5.9d).
The partitioning tracer test indicated that the other recovery wells con-
tained a significant volume of DNAPL in the individual swept zones. These
were 3.2 l for RW-2, 11.6 l for RW-3, 4.6 l for RW-4, 7.2 l for RW-6, and 14 l
for RW-7. RW-3 (Figure 5.9b), RW-4 (Figure 5.9c), and RW-6 (Figure 5.9e)
showed peak PCE concentrations that were approximately 25 times the
initial concentration. RW-7 showed the greatest increase in PCE concentra-
tion, which was more than 80 times the initial concentration (Figure 5.9f).
The PCE concentrations in RW-2 were variable at the beginning of the cosol-
vent flush and reached a concentration of approximately two to three times
the initial concentration (Figure 5.9a). The maximum ethanol concentration
in these wells ranged from 18 to 45%.
Groundwater concentrations of PCE in all of the recovery wells
decreased to initial concentrations following the cosolvent flushing test.
Comparison of average groundwater concentrations in the recovery wells
prior to and post cosolvent flushing showed a high degree of variance and
only 4% decrease in concentrations (Table 5.3). This same comparison for the
three injection wells gave a 99% decrease in concentrations and a similarly
large variance. Averaging the concentrations for both the recovery and injec-
tion wells showed a decrease in average concentration of 62% (Table 5.3).
