Geoscience Reference
In-Depth Information
CHAPTER 1
In-situ
technologies for groundwater treatment: the case of arsenic
Marta I. Litter, José Luis Cortina, António M.A. Fiúza,
Aurora Futuro & Christos Tsakiroglou
1.1
INTRODUCTION:
IN-SITU
TECHNOLOGIES FOR
GROUNDWATER TREATMENT
Conventional technologies for treating contaminated groundwater such as pump-and-treat sys-
tems have several disadvantages due to its high cost, especially when the operation is long lasting
and it becomes impossible to decrease the concentration below the maximum allowable limit
(Benner
et al
., 1999; Harter, 2003; Spira
et al
., 2006). Thus, new
in-situ
technologies are under
development, such as bioremediation, permeable reactive barriers (PRBs),
in-situ
chemical oxi-
dation, multiphase extraction, natural attenuation, electrokinetics (EK), etc. Among all these
methods, PRBs are considered as the most promising ones (Bhumbla
et al
., 1994; Gavaskar
et al
.,
1998; Gu
et al
., 1999; Sacre
et al
., 1997; Waybrant
et al
., 1998).
In-situ
remediation of contaminated soils and aquifers has several advantages compared to
ex-situ
techniques (Eweis
et al
., 1998):
•
the technology is environmental friendly in terms of reducing emission of volatile organic
compounds (VOCs) to the atmosphere compared to excavation, transport and
ex-situ
treat-
ment of the contaminated soil which, by trucks and excavators, contribute to the emission of
greenhouse gases (e.g., VOCs and CO
2
), and hence to global warming;
•
the
in-situ
remediation
may
also
be
applied
if
the
contamination
is
localized
under
roads/constructions or other places that cannot be excavated;
•
in most cases, the total cost of remediation is less using
in-situ
methods in comparison to
excavation and treatment;
•
when extracting contaminated groundwater and treating it above ground (
ex-situ
pump-and-
treat) by a variety of processes (e.g., air stripping, carbon adsorption, bioreactors, chemical
precipitation, etc.) highly contaminated wastes may be produced and have to be disposed in
landfills.
1.2
PERMEABLE REACTIVE BARRIERS
Permeable reactive barriers (PRBs) are a semipassive
in-situ
treatment, which uses a solid reactant
that promotes chemical or biochemical reactions or sorption processes in order to transform or
immobilize pollutants. The technology consists essentially of the construction of a permeable
barrier that intersects the contamination plume, as shown in
Figure 1.1
.
The barrier should allow
a sufficient residence time of the pollutant to allow the occurrence of the reactions with an
acceptable yield (Blowes
et al
., 1996; Burghardt
et al
., 2007; Ludwig
et al
., 2009; Wilkin
et al
.,
2009).
Drilling techniques are normally used to replace the aquifer rock by the reactive material.
The barrier has to be built perpendicularly to the groundwater flow, in the form of a wall. The
materials need to have a high hydraulic conductivity and should intercept the flow; normally,
they consist of a mixture of an inert material with a solid reagent, able to transform the pollutant
1
