In Situ Remediation Technologies - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 961

Run-off

Path oriented
Technologies:

Receptor oriented
technologies:

Source Oriented
Technologies:

Quality standards /
Thresholds based on
chemical status/ trends /
Interception measures

Groundwater Directive
Prevent / Limit
Measures

Ecological Quality Status aquatic
and terrestrial ecosystems, drinking
water standards,
Human health risks

Fig. 21.3 Source-path-receptor approach and source, path and receptor oriented technologies

Physical techniques like removal of a floating layer by pumping are described in
the literature, e.g., pump and treat , slurping or bioslurping (Alleman and Leeson
1997 ). Especially, removal of floating layers with pure product is very efficient as
further spreading in the environment will be avoided. However, pump and treat
technologies are less efficient when only the dissolved fraction in the groundwa-
ter can be removed (Hoffman 1998 ). In this situation the use of steam injection
(Smart 2005 ), surfactant enhanced cleaning (Hayworth 1997), or co-solvent flush-
ing (Ramakrishnan et al. 2005 ) may be useful. After the first applications of pump
and treat in the early 1990s, it became clear that continuous pumping was often
not cost-effective, as a large fraction of contaminants was tightly bound to the soil
matrix, especially for contaminants with a high K d value as is shown in Fig. 21.1 .
Thereafter intermittent pumping of contaminated groundwater was applied as an
alternative.
Physical techniques for volatile contaminants were developed in a similar way, as
continuous stripping of soil gas was soon followed by intermittent soil gas removal,
like venting and intermittent venting. One of the disadvantages of severe strip-
ping was that, after treatment, catalytic thermal treatment or biofiltration had to
be applied to the stripped soil gas. Shortly thereafter, it became clear that biodegra-
dation could also be applied by the endogenous microbial population in the vadose
zone, and technologies such as bioventing were introduced (Malina et al. 2002 ). The
extra gas that was introduced in the soil was not specifically directed to strip the
volatile contaminants, but the introduced oxygen that came with the air was used
for enhanced biodegradation for BTEX contaminant as well as for other volatile
TPH compounds. For the saturated zone, volatile contaminants can be removed by