Environmental Engineering Reference
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MWG107B
Upgradient
MWG101B
Denit. PRB
MWG112B
between
MWG104B
ZVI PRB
MWG110B
Downgradient
Monitoring well
FIGURE 7.11
TOC concentrations measured along cross-section C-C′ for the B series wells.
elevated viscosity, and precipitation. In the most recent round of monitoring,
only a slight organic odor could be noted within some monitoring wells of
the dentirification PRB. This may indicate that either the excess carbon has
been flushed out of the system or more likely it is being consumed by bac-
teria within the system, with the sawdust now providing the predominant
source of carbon within the system.
Yet another factor to be noted is the low concentration of TOC measured in
monitoring well MWG112 at all depths, located downgradient of the denitri-
fication PRB and upgradient of the ZVI PRB. This suggests that the natural
aquifer material present between the two PRBs is acting as a buffer and is
resulting in a reduction of TOC concentration in the influent groundwater to
the ZVI PRB. This will likely minimize the potential passivation of ZVI due
to DOC emanating from the denitrification PRB.
7.9 Nitrate Concentrations
Nitrate (as N) concentrations measured during the quarterly monitoring pro-
grams for B series wells along the plume centerline (Section C-C′ in Figure
7.10) are presented in Figure 7.12. The results indicate that the denitrifica-
tion PRB is effectively removing more than 99% of the nitrate (as N) from
the influent groundwater at this depth. This ensures that passivation of the
downgradient ZVI PRB by nitrate will be minimal.
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