Permeable Reactive Barriers in Europe - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 278

PRBs can be designed to treat any contaminated fluid, including contami-
nated soil gases, but are most commonly used to remediate contaminated
groundwater within aquifers. The reactive media used in PRBs typically
enhances the chemical or biological transformation of the pollutant(s), or
retards its migration by sorption or immobilization of the pollutant onto the
reactive media (Carey et al., 2002).
13.1.1 Engineered PRBs
The U.K. and German PRB guidance documents stress that a PRB should
be engineered. The U.S. PRB guidance provides a more extended definition,
which includes injection zones. Although the PRB concept was first devel-
oped in North America in the early 1990s, European projects have also played
an important part in the development of the technology. The first full-scale
zero-valent iron (ZVI) PRB in Belfast, U.K., had already been planned and
erected in 1994. The first German full-scale ZVI PRB at Tübingen was erected
in 1998, whereas the full-scale Austrian PRB at Brunn am Gebirge (a suburb
of the Austrian capital Vienna) employed granular-activated carbon (GAC)
in 1999. The total number of active European projects has reached around
50 by 2014, of which more than 25 are full scale. Some European suppliers
offer sophisticated turnkey solutions for PRBs, while numerous research and
development (R&D) trials have been performed since 2000, ranging in scale
from pilot to full-scale applications.
During the evolution of the technology, two general types of construction
emerged:
1. The continuous reactive barrier (CRB) entirely consists of a perme-
able zone of a reactive material that is installed in the path of a con-
taminant plume, for instance in a trench, and captures the entire
plume. Manipulation of the groundwater flow or control over it or
over the reactive material(s) is not possible using this type of con-
struction (Figure 13.2).
2. The funnel-and-gate system (F&G) is characterized by impermeable
walls that intercept the contaminated plume and direct it toward
a permeable section loaded with the reactive material (gate) (see
Chapter 3).
In the early 1990s, it was believed that both design types would work
effectively for several decades in the subsurface, even without maintenance,
once installed. For this reason, it was thought that PRBs did not require easy
access to the reactive material or the groundwater, as malfunctions were
thought to be unlikely.
During subsequent development of the PRB technology, the F&G design
has been significantly modified at numerous sites, especially across Europe,
to address special issues, such as handling a heterogeneous groundwater