Environmental Engineering Reference
In-Depth Information
~22 Months Post-Flush
~25 Months Post-Flush
C7
C7
C3
C3
C4
C4
MW-512
80 mg/L
MW-512
MW-513
MW-513
MW-514
MW-514
C2
MW-505
C2
MW-505
C1
C1
70 mg/L
MW-506
MW-506
MW-509
MW-510
MW-511
MW-509
MW-510
MW-511
60 mg/L
MW-507
MW-507
50 mg/L
40 mg/L
30 mg/L
~31 Months Post-Flush
~28 Months Post-Flush
20 mg/L
10 mg/L
C7
C7
0 mg/L
C3
C3
C4
C4
MW-512
MW-512
MW-513
MW-514
MW-513
MW-514
C2
MW-505
C2
MW-505
C1
C1
MW-506
MW-506
MW-509
MW-510
MW-511
MW-509
MW-510
MW-511
MW-507
MW-507
Figure 5.33
Chloride contour plots over the groundwater monitoring (80 mg/l = 2.26
m
M
).
since ethanol is the parent product (Equation 5.2). After the significant
decrease in ethanol, it is expected that the microbial population would shift
to using acetic acid as the electron donor so that there would be a decrease
in these concentrations as well. The acetic acid contour plots show this trend
(Figure 5.35 to Figure 5.37). The highest measured concentration of acetic
acid was approximately 2.5 m
M
, which is 100 times less than the maximum
ethanol concentration of 260 m
M
. This would indicate that a significant
amount of the ethanol is being completely degraded to carbon dioxide and
hydrogen gas.
The hydrogen gas survey conducted approximately 1 year after the
cosolvent flushing test indicated that high levels of hydrogen were being
produced (Figure 5.38). Concentrations of hydrogen gas in wells near the
injection/extraction area were more than 2 μ
M
, and downgradient loca-
tions measured from 5 to 30 n
M
. Hydrogen gas is produced from the
oxidation of ethanol and can be utilized by microorganisms responsible
for the catabolic and cometabolic reductive dechlorination of PCE and its
daughter products.
Background concentrations of sulfate at the site were approximately 40
mg/l. All locations showed a decrease in sulfate concentrations over the
monitoring period (Figure 5.39). Sulfate was removed from the area imme-
diately downgradient and including the injection/extraction zone within 3
months of the cosolvent flushing test (Figure 5.40 to Figure 5.42). After
approximately 14 months, the area of sulfate removal expanded to include
most of the downgradient wells. Even MW-506, which was located upgra-
dient of the flushing area, showed a decrease in sulfate concentrations. The
contour plots of this data depict the sulfate removal and give a strong
