Environmental Engineering Reference
In-Depth Information
21.1 Introduction
21.1.1 Background of In Situ Remediation
In the early 1990s,
In Situ remediation
of contaminated sites started to develop
as it became clear that many sites are too large to excavate and treat thereafter.
Especially In Situ bioremediation attracted attention after the first publications
by McCarty on the sequential biodegradation of TCE (trichloroethylene) at the
St. Joseph site near lake Michigan (McCarty et al.
1991
) and the prosperous out-
look for bioremediation shortly thereafter (McCarty
1991
). Besides bioremediation,
physical technologies were also developed in that period, such as
pump and treat
,
soil vapor extraction
and
air sparging
(Hutzler et al.
1991
; Mackay and Cherry
1989
; Marley et al.
1992
). Subsequently, bioremediation and physical technologies
were combined, such as pump and treat technologies which were used to introduce
nutrients or co-substrates to stimulate bioremediation, and soil vapour extraction
and air sparging were combined with bioremediation into bioventing technologies
(Hoeppel et al.
1991
; Malina et al.
1998
).
Also more energy intensive technologies were proposed, such as
electro reclama-
tion
(Lageman et al.
1989
), and
thermal treatment
and
vitrification
(Dragun
1991
).
However most In Situ applications in the 1990s were in the field of bioremediation
combined with physical removal strategies.
Since the early 1990s, when the first In Situ field studies were performed, it
became clear that In Situ processes are rather slow and residual concentrations
were often above legal Remediation objectives. Together with the rapidly increasing
number of sites detected as contaminated, a transformation in policies and in field
applications was observed from removal of all contaminants to reduction of risk at
affordable costs. The
bioavailability
of contaminants is a key factor in Risk Based In
Situ bioremediation. From the risk perspective, bioavailability determines whether
there is a risk for specific receptors. From the remediation perspective the availabil-
ity of contaminants determines whether in-situ remediation, and to what residual
concentration, is possible (Cuypers et al.
2000
; Semple et al.
2003
; Volkering et al.
1998
).
In research, technologies for the concept of Source-Path-Receptor of con-
taminants in soil and groundwater started to develop. Especially in the period
1995-2005 most attention was paid to mobile contaminants like BTEX (ben-
zene, toluene, etheylbenzene, xylene) and chlorinated solvents. Many concepts in
blocking the path of the flow of contaminants within the groundwater were devel-
oped, such as bioscreens, biobarriers, funnel and gate systems, permeable reactive
barriers.
Technologies for removal of hydrophobic organic contaminants, such as PAHs
(polycyclic aromatic carbons), PCBs (Polychlorobiphenyls) and chlorinated pesti-
cides, received less attention in this period. However, this development was also
the result of many availability studies in which it was shown that many hydropho-
bic organic contaminants are often tightly bound to soil organic matter. When such
contaminants are tightly bound to soil, the risk for uptake by a receptor is assumed
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