Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 43

Electrical separation is based on an electric field in the soil between inserted
electrodes, which forces the migration of pore water or groundwater, including met-
als and organic contaminants. It is a relatively new technology and, therefore, still in
the experimental stage, for which further development is necessary. It might, how-
ever, be an alternative for the remediation of clayey soils when 'Pump-and-Treat'
methodologies are not efficient. Amrate et al. ( 2005 ), for example, demonstrated a
successful migration of lead in a highly contaminated soil near a battery plant in
Algiers, Algeria, where EDTA was added to enhance lead transport.
A spectacular extensive remediation technology that has gained enormous popu-
larity since the mid 1990s is based on biodegradation of organic contaminants and
dilution, and is often called Natural Attenuation . Indigenous or cultured organisms
can be used for biodegradation. In spite of the sometimes high starting costs, the
overall budget for this Risk Management procedure is generally low. In addition,
it allows for a minimal disturbance of the natural conditions in the soil or ground-
water, and there are limited engineering activities needed at the site. Moreover, it
even offers opportunities for difficult sites with clayey soils and difficult contam-
inants such as chlorinated hydrocarbons, even under anaerobe conditions. Natural
Attenuation is often combined with ex situ remediation techniques, such as removal
of the source. The adage is: use the natural self-cleaning capacities of the soil as
much as possible, stimulate natural conditions when necessary and use ex situ reme-
diation technologies only when strictly needed. The success of Natural Attenuation
depends primarily on the type of organic contaminant and the performance of the
soil ecosystem. The latter depends on the organisms present. Zytner et al. ( 2006 ),
for example, demonstrated the important contribution of fungal metabolism for the
degradation of branched hydrocarbons. For this reason the chemical and physical
characteristics of the soil and the artificial oxygen and nutrient supply are dominant
factors.
In situ Bioremediation of organic contaminants is especially difficult in low per-
meability soils. Athmer ( 2004 ) described a procedure for integrating electro kinetics
with in situ treatment for the remediation of TCE (trichloroethylene) contaminated
clay soils in Paducah, Kentucky, USA, to address this problem. It generated a
uniform migration of trichloroethylene through the soil to treatment zones.
Peter et al. ( Chapter 22 of this topic) give a detailed description of Natural
Attenuation and of its practical possibilities.
As specific applications, 'bio-screens' are used, that is, zones with an active,
often stimulated, degradation at strategic positions in the soil system, or Funnel-and-
Gates techniques, in which contaminants are led to zones with an active degradation.
Several materials have been proven to be effective in Solidification/Stabilization
(aka: immobilization , or fixation) of heavy metals in soils. A proven method to fix-
ate metals in soils is mixing the soil with lime (liming) or cement. Yukselen and
Alpaslan ( 2001 ), for example, successfully immobilized copper, and iron in soils in
an old mining and smelting area located along the Mediterranean coast in northern
Cyprus. They showed that an additive/soil ratio of 1/15 (on mass basis) resulted
in the optimal immobilization, for both lime and cement. This ratio very much
depends, of course, on the soil type and soil properties, mainly pH. Tlustoš et al.