Two Decades of Application of Permeable Reactive Barriers to Groundwater Remediation - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 35

installations involving construction may involve substantial capital invest-
ment. However, the benefit of low or negligible costs post construction allow
a life cycle analysis to conclude that economic value comes from designing
the PRB for successful operation over as long a time as possible.
An important lesson with respect to overall costs for a PRB is that it is
much easier to test the functionality of PRB treatment media under labora-
tory conditions than it is under field conditions. However, this does not pre-
clude the occasional “investment” of a small-scale pilot test to assure a final
PRB design that will meet long-term remedial objectives. We anticipate that
cost performance data will be collected from a greater number of sites—in
particular those involving novel reactive media—to better confirm the long-
term efficacy of PRB technology for treating groundwater plumes. Finally,
while a return on investment (ROI) is important for any application, past
experience indicates that compared to active energy-intensive remedies, the
ROI likely is only a few years compared to the overall several decade life of
typical contaminated site.
2.4 Recent Advances
When considering what recent advances in PRB technology have been valu-
able, what future improvements would be beneficial is also an important
exercise. Because the PRB technology now is approaching 25 years in use,
and many may consider the technology to be a “developed” remedial mea-
sure, we may in fact find more utility in discussing potential future improve-
ments. In this vein, a discussion of future improvements may follow the
outline of advancement categories proposed herein and as considered by
ITRC in its 2011 PRB Technology update (ITRC, 2011):
• Construction methods
• Reaction rates
• Hydraulic design improvements
• Monitoring improvements
• Treatment of mixed plumes and emerging contaminants
• Longevity enhancements
• Cost performance improvements
• Closure and decommissioning methods
Over the past 20 years, we have seen improvements in construction meth-
ods by use of one-pass trenching, injection methods, and the use of recycled or
“green” treatment materials. Reaction rates are generally not much different