Permeable Reactive Barriers: Cost-Effective and Sustainable Remediation of Groundwater - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 12

(VOCs) without bringing it to the surface. The target contaminant groups
for this technology are halogenated VOCs, semivolatile organic compounds
(SVOCs), and fuels. A circulation pattern is created in an aquifer by drawing
water into and pumping it through a well and then reintroducing it without
reaching the surface (Khan et al., 2004). PRB is a passive remediation technol-
ogy installed in situ , allowing groundwater to flow under the natural gradi-
ent through a reactive cell where a reactive medium degrades or captures
the contaminants (Thiruvenkatachari et al., 2008). Pump-and-treat systems
(PTS) have been used for more than 20 years in the remediation of ground-
water contamination. In these systems, the contaminated groundwater is
extracted from the ground, treated above ground, and finally discharged or
reinjected (Naidu, 2013; USEPA, 1999a,b).
Other groundwater remediation technologies are summarized in Table
1.2. These vary from passive to active remediation technologies and have
significant differences in their nature of operation and cost (FRTR, 1998).
For a variety of reasons summarized below, it is currently difficult to
develop accurate comparisons of remediation technology costs in many situ-
ations (National Research Council, 1997).
• Costs reported under a set of local conditions (technology costs are
sensitive to site-specific geological, geochemical, and contaminant
conditions, especially for in situ technologies).
• Technology vendors report costs using a variety of different metrics
that cannot be compared directly (costs may be reported as $ per vol-
ume treated, reduction in contaminant concentrations achieved, con-
taminant mobility reduction achieved, mass of contaminant removed
or surface area treated).
• Technology providers do not report the variable costs just “up
and running” costs are given. This may be acceptable if the user
only wants to compare the cost of installed operations, but the user
is usually interested in the overall project cost. If certain remediat-
ion technologies have large and variable initial costs, they may
not be competitive, even if the “up and running” costs appear
competitive.
• Inconsistencies in the way costs are derived. Comparisons of unit
costs have little meaning unless there is uniformity in the underly-
ing methodologies and assumptions used in calculating the costs.
For example, if different interest rates are used to estimate the costs
of a cleanup system over its entire life cycle, conclusions about the
cost competitiveness of a technology can vary widely.
This loss of compiled cost information greatly hinders dissemination of
consistent cost data and makes it difficult for a new technology provider to
develop comparative cost information. Furthermore, even where information