Environmental Engineering Reference
In-Depth Information
all affected groundwater at a site flows through the PRB. More accurately, the
primary use of a PRB is to eliminate or substantially reduce the mass flux of
the target contaminant(s) to areas located immediately downgradient of the
PRB alignment. The PRB is not, in its typical intent, used as a source remedia-
tion technology; but is more correctly a source control remediation technology.
The PRB may also be used as a receptor protection technology if its primary
purpose is to protect sensitive receptors located either near or far from a
potential contaminant source.
As remediation technologies for contaminated groundwater have pro-
gressed since the 1980 genesis of the U.S. Superfund Program, the intended
movement away from energy-intensive groundwater pump and treat, to
hydraulically passive treat-in-place, or in situ , methods, has allowed technol-
ogies such as the PRB to develop from purely a research-and-development
exercise to a proven remediation technology used worldwide. While pump-
and-treat still is used for many groundwater remediation projects, the general
progression from active to passive technologies has occurred for a number
of reasons including the intent to find less expensive, more focused, more
resource conservative methods to protect environmental receptors from
being negatively impacted by groundwater contaminants.
As introduced above, the PRB technology, which has been the focus of
hundreds if not thousands of technical articles and publications is consid-
ered, for example, a “remediation concept” whereby affected groundwater is
allowed to flow through, or is routed through, an emplaced subsurface zone
of treatment media that has geochemical or biochemical properties appro-
priate for either destroying, immobilizing, or altering the molecular form of
the contaminant sufficiently enough to render it harmless.
Early versions of the PRB concept were used to neutralize acidic water
using limestone filters off of mine tailings piles (Pearson and McDonnell
1975); the first commercial PRB using granular iron metal was con-
structed in 1994 to destroy chlorinated aliphatic compounds in ground-
water (Warner et al., 1998) following the development of the technology by
researchers at the University of Waterloo (Gillham and O'Hannesin 1994),
and a number of pilot tests of PRBs for treating radioactive constituents in
groundwater were attempted in the mid- to late 1990s (Naftz et al., 2002).
Reasonably, it makes sense that since the early 1990s, several hundred
pilot tests and fewer, though still a substantial number, of the full-scale
remedies involving the PRB concept have been implemented worldwide.
Today, with the focus on sustainable and green remediation, the PRB is
arguably one of the most sustainable approaches considering that the old-
est systems, now more than 15 years later, have functioned successfully
since their installation to treat contaminated groundwater in situ without
the need to apply energy or pump water—a claim that few other treatment
methods can make.
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