Environmental Engineering Reference
In-Depth Information
cis-DCE Formation
70000
60000
50000
y = 52.702x
R
2
= 0.6131
40000
30000
20000
10000
y = 1.0906x
R
2
= 0.489
0
−
200
0
200
400
600
800
1000
1200
Time (Days)
C2
C3
MW-510
MW-514
Linear (MW-510)
RW-007
Linear (C2)
Figure 5.47
Production of cis-DCE from PCE by microbial reductive dechlorination
supported by the residual ethanol from the cosolvent flush at the Sage's site.
If we include the mass of residual DNAPL PCE (26 l) that was estimated
to remain in the swept volume and use the average rate of cis-DCE produc-
tion of 5.54 μg/l/day, it would take more than 1000 years for complete
removal. This calculation assumes that there are no mass transfer limitations.
Similar analysis of PCE removal rates for the RW-wells gives an average
rate of -37.9 μg/l/day, which is more than six times the rate of cis-DCE
formation (Figure 5.48). Table 5.7 is a compilation of the rates of PCE removal
and correlation coefficients for the individual wells. Using the average rate
of removal for the RW-wells, it would take approximately 3 years for com-
plete removal of the dissolved phase PCE and approximately 200 years for
complete removal of the residual DNAPL PCE. Again, it is assumed that
there are no mass transfer limitations.
5.5.5.4 Total mass removal
The total masses of cis-DCE and PCE were calculated for each sampling
event based on the Surfer contour plots. The masses were put on a relative
basis by dividing by the initial mass measured before the cosolvent flushing
test. Rate constants for each compound were obtained by fitting a linear
regression to the data (Figure 5.49).
The rate constant for PCE was -0.56/year and for cis-DCE was 0.81/
year for the site. Converting these rate constants to half-lives gives values
of 1.2 and 0.9 years, respectively. These values indicate that the activity
