Environmental Engineering Reference
In-Depth Information
than when the PRB materials were first conceived in the 1990s and 2000s and
research into newer and better PRB materials may have waned. However,
there likely will be improvements primarily in concert into researching
new PRB treatment materials for emerging contaminants. Hydraulic design
improvements specifically will occur consistent with comprehensive site
characterization programs. With the collection of thorough and complete
subsurface information, higher performance hydraulic designs are more
likely to be developed providing appropriate design techniques where both
engineering and numerical analysis are used. Different geometric designs
that help to capture contaminant plumes without alternating ambient flow
and with less potential for creating hydraulic bypass conditions are not tech-
nological advances, but rather, are the result of developing a better three-
dimensional understanding of the contaminant distribution and hydraulic
characteristics of a site.
With regard to longevity, again, technological advances in materials are
less likely to create longer-lasting PRBs compared to more fully understand-
ing the issues (such as geochemical competition from inorganic constituents,
i.e., nitrate as a cause of reducing performance by ZVI as a treatment media)
that cause PRBs to age more quickly. Design considerations that reduce the
potential plugging from carbonate-shift mineralization will result in a lon-
ger-lasting PRB. New advances in “demineralizing” PRB materials may be in
the future, but most research to date has not provided evidence of effective
and inexpensive rejuvenation techniques, with the exception of reloading
liquid organic carbon into some types of bioremediation PRB systems.
What we still do not have a good handle on is closing and decommission-
ing PRBs, chiefly because few if any PRBs have been closed due to regu-
latory completeness of a remediation project. The expectation is that most
PRBs will remain in place if the treatment material becomes exhausted or
if the remediation program is completed. PRBs are composed primarily of
earth materials or native components and should not negatively impact a
groundwater resource even when exhausted. The exception may be PRBs
used for remediation of radioactive plumes—in this case, it still may be more
appropriate to keep the PRB in place until radioactivity is at a nonproblem-
atic level, or maintain sufficient monitoring to avoid potential problems for
as many years as necessary.
The most well received advances will likely continue to be in the areas of
cost performance. The ability to construct PRBs from local, green, or abun-
dant natural materials will allow the technology to be more universally used
in economically disadvantaged areas to protect important and sensitive
water resources and receptors. The use of green compost—native sorptive
materials such as sawdust and woodchips—and inexpensive construction
methods in areas downgradient of leaking landfills or septic systems will
create a new market for inexpensive PRBs worldwide and thus, reduce the
deleterious nature of contaminant migration for a large part of the world's
population.
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