268
Permeable Reactive Barrier
One of the subsamples contained iron that was clumped together, which
could be indicative of mineral precipitation. This subsample returned the
highest percentage of sulfur—0.21%. Assuming that all of the sulfur was
present as FeS, the resultant loss in porosity in the first 0.1 m of the barrier
was estimated to be <0.5%. Carbonate analyses suggested that carbonate precipitates had caused <5% loss in porosity in the first 0.1 m of the barrier, with
lower losses further into the iron. The RAMAN spectroscopy qualitatively
confirmed the presence of carbonate, sulfur, and iron mineral species on the
iron grains. Although, microbial populations—evaluated using standard
microbial enumerations (plate counts) and phospholipid fatty acid (PLFA)
analysis—were found to be larger than those measured in similar studies,
there was no evidence of significant biofouling (EnviroMetal Technologies
[ETI], 2001).
12.9 Full-Scale Reactive Iron Barrier Assessment
The first 19 months of sampling and analysis represented the formal assessment period for the pilot-scale reactive iron barrier. The data were assessed
to evaluate the effect of the site’s high influent concentrations of chlorinated solvents and TOC on the reductive dechlorination reaction kinetics.
Reaction half-lives generally appeared to be higher than those published for
other sites. This was thought to be a result of the relatively high TOC arising
from the site’s historical swampy conditions. However, the overall average
chlorinated solvent MR was 80%–90%. Temporal trends were evident, but
these were not consistent with increasing depth or TOC. Another factor that
reduced apparent MR was the presence of EDC and (to a far lesser extent)
DCM in the inflowing groundwater, which are not known to be degraded
by the ZVI.
This pilot-scale evaluation had demonstrated that ZVI could be used successfully to degrade a broad range of dissolved CHCs in a geochemically
complex aquifer. As a result, Orica began planning the installation of a fullscale reactive iron barrier, up to 300 m long, 0.4 m thick, and 7 m deep, to
protect Springvale Drain. John Vogan of ETI had noted in a CLC meeting
in late 1999 that at that time, a reactive iron barrier of that size would have
been the biggest in the world. It also became apparent that no domestic supplier of ZVI could manufacture the required quantity within a suitable time
frame; so, investigations into sourcing the material from overseas began in
late 2000.
A number of design configurations were evaluated to maximize the interception of the non-EDC plumes, and also minimize the potential impediments to the future development of the land on which the barrier would
be installed. Additional monitoring wells and multilevel piezometers were
Permeable Reactive Barrier
One of the subsamples contained iron that was clumped together, which
could be indicative of mineral precipitation. This subsample returned the
highest percentage of sulfur—0.21%. Assuming that all of the sulfur was
present as FeS, the resultant loss in porosity in the first 0.1 m of the barrier
was estimated to be <0.5%. Carbonate analyses suggested that carbonate precipitates had caused <5% loss in porosity in the first 0.1 m of the barrier, with
lower losses further into the iron. The RAMAN spectroscopy qualitatively
confirmed the presence of carbonate, sulfur, and iron mineral species on the
iron grains. Although, microbial populations—evaluated using standard
microbial enumerations (plate counts) and phospholipid fatty acid (PLFA)
analysis—were found to be larger than those measured in similar studies,
there was no evidence of significant biofouling (EnviroMetal Technologies
[ETI], 2001).
12.9 Full-Scale Reactive Iron Barrier Assessment
The first 19 months of sampling and analysis represented the formal assessment period for the pilot-scale reactive iron barrier. The data were assessed
to evaluate the effect of the site’s high influent concentrations of chlorinated solvents and TOC on the reductive dechlorination reaction kinetics.
Reaction half-lives generally appeared to be higher than those published for
other sites. This was thought to be a result of the relatively high TOC arising
from the site’s historical swampy conditions. However, the overall average
chlorinated solvent MR was 80%–90%. Temporal trends were evident, but
these were not consistent with increasing depth or TOC. Another factor that
reduced apparent MR was the presence of EDC and (to a far lesser extent)
DCM in the inflowing groundwater, which are not known to be degraded
by the ZVI.
This pilot-scale evaluation had demonstrated that ZVI could be used successfully to degrade a broad range of dissolved CHCs in a geochemically
complex aquifer. As a result, Orica began planning the installation of a fullscale reactive iron barrier, up to 300 m long, 0.4 m thick, and 7 m deep, to
protect Springvale Drain. John Vogan of ETI had noted in a CLC meeting
in late 1999 that at that time, a reactive iron barrier of that size would have
been the biggest in the world. It also became apparent that no domestic supplier of ZVI could manufacture the required quantity within a suitable time
frame; so, investigations into sourcing the material from overseas began in
late 2000.
A number of design configurations were evaluated to maximize the interception of the non-EDC plumes, and also minimize the potential impediments to the future development of the land on which the barrier would
be installed. Additional monitoring wells and multilevel piezometers were