Chlorinated solvent contaminated soils and groundwater: field application of the solvent extraction residual biotreatment technology - Bioremediation of Recalcitrant Compounds - page 100

~22 Months Post-Flush

~25 Months Post-Flush

C7 C7

C3

C4 C3

C4

MW-512

MW-512

MW-514 MW-513

MW-514 MW-513

C2

80000 ug/L

MW-505 C2

MW-505

C1 C1

70000 ug/L MW-506

MW-506

MW-509
MW-510
MW-511

MW-509
MW-510
MW-511 60000 ug/L

MW-507

MW-507

50000 ug/L

40000 ug/L

~28 Months Post-Flush

~31 Months Post-Flush

30000 ug/L

20000 ug/L

10000 ug/L

C7

C7

0 ug/L C3

C4 C3

C4

MW-512

MW-512

MW-514 MW-513

MW-514 MW-513

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 5.17 PCE contour plots over the groundwater monitoring period (80,000
μg/l = 480 μ M ).

of ethylene show a consistent trend of formation in the same wells that
showed relatively high ethanol concentrations over time (MW-505, MW-509,
C1 to C3, RW-3, and RW-7). The contour plots for this data indicate the area
of main activity is from the injection/extraction area downgradient to well
C2 (Figure 5.27 to Figure 5.29).
The formation of the daughter products of PCE is an indication that in
situ reductive dechlorination is beginning to occur. The process appears to
have begun initially in the area where the cosolvent extraction was con-
ducted and later in locations downgradient of the targeted source area.
Production of chloride is concomitant with the reductive dechlorination
of PCE, and because it is a relatively nonreactive anion, one would expect
to see an increase in chloride concentrations over time. Background chloride
concentration was less than 10 mg/l except in the injection/extraction zone,
where concentrations were as high as 20 mg/l. Overall, there was a trend
of increasing chloride concentrations over time (Figure 5.30). In particular,
monitoring wells that showed the formation of cis-DCE also had an increase
in chloride concentrations. Data from the RWs did not show this relationship
and had more variable concentrations of both cis-DCE and chloride. Contour
plots of chloride do show an increase in concentrations in the area immedi-
ately downgradient of the injection/extraction zone within 1 month of the
cosolvent flushing test (Figure 5.31 to Figure 5.33). After approximately 1
year, this area of higher chloride concentrations appears to have moved
farther downgradient to the area of C1 and C2.
The maximum measured chloride concentration was approximately 2
m M , which is almost four times the maximum measured PCE concentration
of 500 μ M . This compares well to the complete dechlorination of PCE, which