Environmental Engineering Reference
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• Characterize the degradation products (to confirm contaminant
destruction and to determine whether any more harmful substances
might be formed)
• Quantify Eh and pH changes (although the redox potential of the
groundwater samples changed following sampling and transport to
Canada, the step change in Eh as the groundwater passed through
the ZVI was a relevant parameter to monitor to evaluate the PRB
performance)
• Monitor changes in inorganic geochemistry (in part to indicate
whether mineral fouling of the reactive iron barrier might occur)
• Characterize microbial activity (which could result in biological
fouling of the reactive iron barrier might occur)
• Compare Australian-sourced granular iron reactivity and perfor-
mance (including potential longevity)
• Provide predesign data for a potential pilot-scale reactive iron barrier
ETI issued results of the completed column trials to Orica in August 1998.
The trials concluded that the principal target contaminants CTC and PCE
were degraded, but the reaction half-lives higher than ETI had previously
experienced with other sites' groundwater and other iron sources. ETI attrib-
uted the slower degradation rates to the presence of very high concentra-
tions of DOC (>500 mg/L) in the Botany groundwater. ETI postulated that
the DOC could be coating the iron surface or entraining PCE in solution,
preventing reaction. The column trial results also indicated typical Eh val-
ues, but the groundwater pH—in both the influent and effluent—was lower
than at other clients' sites. There were no signs of biological fouling or min-
eral precipitation, which were important considerations for barrier longev-
ity. Importantly, an Australian iron source—Master Builders Australia Pty
Ltd—was also validated.
12.5 Pilot-Scale Barrier Design
As indicated above, the column trials were also intended to provide pre-
design data for a potential pilot-scale reactive iron barrier. On the basis of
ETI's calculations of contaminant half-lives (45 h for PCE and 1-2 h for CTC)
and the site conditions (such as groundwater velocity), the following design
parameters were recommended:
• Barrier width (i.e., perpendicular to the groundwater flow): 5 m
• Barrier height: 3.5 m (installed 4 m bgs)
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