Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 45

Incineration, Mechanical soil aeration, Neutralisation, Open burn/Open detona-
tion, Physical separation, Phytoremediation, Soil vapour extraction, Soil washing,
Solification/Stabilization, Solvent extraction, Thermal desorption, and Vitrification.

1.6.4.4 Barriers

Barriers are used to isolate contaminants at contaminated sites from the sur-
roundings and, hence, to protect any protection targets in the surroundings of the
contaminated site. Compacted soil materials are recognized liners. Clay, or clayey
soil material, is the most obvious natural barrier material. They both have a low
hydraulic permeability and a chemical buffering capacity through adsorption. Kabir
and Taha ( 2004 ), for example, demonstrated an effective barrier function of com-
pacted sedimentary granite residual soil material for the isolation of contaminants
in landfills. They showed that this material has a hydraulic conductivity lower
than the suggested limit (1 10 − 7 cm/s) of the various waste regulatory agencies

in the USA. In addition, it has adequate strength for stability, and exhibits small
shrinkage potential upon drying. Qian et al. ( 2002 ) specified the requirements of
soil materials as effective barriers, in terms of contribution of silt and clay, plas-
ticity, and limitations to the contribution of gravel-size materials and chunks of
rock.
Several waste materials such as fly ash could be used a barrier material.
Sivapullaiah and Lakshmikantha ( 2004 ), for example, demonstrated that the addi-
tion of bentonite to fly ash improves the chemical buffering function and the
geotechnical properties of the barrier. Kaolonite and bentonite (a commercially
available high swelling clay) are artificial alternatives for barrier materials.

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1.6.5 Ecological Recovery

A problem with many remediations, especially ex situ remediation measures, is
that the soil ecosystem, vegetation and above-ground fauna generally are nega-
tively impacted, at least on the short term. In case of Dig-and-Dump technologies,
the habitats, the organisms and the seed pool are removed from the site. Ex situ
thermical treatment results in total elimination of soil organisms and organic mat-
ter. Especially when a remediation is triggered because of unacceptable ecological
risks, the question is relevant if the ecological benefits on the longer term counteract
the negative impact on the short term. The possibilities and timeframe for ecolog-
ical recovery strongly depend on the type of soil that is applied in the final stage
of the remediation. Especially clayey soil material high in organic matter speeds
up the recovery process. The application of comparable soil as the wider environ-
ment, however, improves the development of a regionally appropriate ecosystem.
The effects on above-ground fauna can be reduced through a stepwise remediation
procedure, in which in different stages only a part of the site is remediated, so that
recolonisation of organisms in the 'new soil material' can take place from the parts
that have not yet been remediated.