Environmental Engineering Reference
In-Depth Information
to be minimal. Ironically, an increasing number of research papers show that, if the
risk for uptake in the food chain is minimal, also the chance for removal of contam-
inants is minimal. This implies that high residual concentrations, when proven to
be non-available, should not lead to a high risk for human beings, soil organisms,
groundwater or agricultural crops. Such a strategy was also studied for heavy metal
immobilization at field scale. Different soil additives with a high binding capac-
ity for heavy metals had a positive impact on re-vegetation in highly heavy metal
contaminated sites (Vangronsveld et al. 1996 ).
In 1997, Natural Attenuation (NA) caused a breakthrough at the “International
Symposium In Situ and On Site Bioremediation”, in New Orleans. A devel-
opment of Natural Attenuation to Monitored Natural Attenuation (MNA) and
Enhanced Natural Attenuation or Engineered Natural Attenuation (ENA) was
observed in the subsequent symposia in the USA as well as in Europe at the ConSoil
conferences.
Technologies for In Situ source treatment by chemical oxidation of soil contam-
inants were initially introduced at the laboratory scale, such as (Gates and Siegrist
1995 ) and (MacKinnon and Thomson 2002 ) who performed lab scale experiments
with MnO 4 - for oxidation of PCE (Perchloroethylene) pools of pure product. It
was stated by ISTRC ( http://www.estcp.org /) that up to 1999 no field designs were
available for In Situ oxidation. Also the use of Fenton's reagent was known for
many years as oxidant in waste and wastewater treatment, and was reported to acti-
vate the per sulphate oxidation for removal of TCE at lab scale, in 2004 (Liang
et al. 2004a , b ). Since about 2002, field scale applications of source treatment by In
Situ Chemical Oxidation (ISCO) were performed with success (Plaisier et al. 2003 ),
leading to a review of the use of Fenton reagent for soil remediation (Pignatello
et al. 2006 ).
21.1.2 Scope
In this Section, first the principles of In Situ remediation will be discussed
with respect to equilibrium and non-equilibrium conditions. The primary focus
is on In Situ remediation of organic contaminants in the subsoil of the vadose
and water saturated zone. No attention is paid to phytoremediation or to In
Situ treatment of sites contaminated with heavy metals, nitrates, cyanides or
ammonia.
Non-equilibrium conditions are required for remediation, which can be reached
by changing specific environmental factors. Often, environmental factors may limit
the remediation at a specific site. Therefore, environmental factors are key to the
success of an In Situ remediation. The role and possible engineering of several
environmental factors will be discussed. Thereafter a variety of Risk Based In Situ
technologies will be discussed that can be applied at the source, along the path or
at the receptor of the contamination. Finally, an outlook is presented on the combi-
nation of In Situ remediation with other societal processes in industrial and urban
areas.
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