Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 15

Residential land use could be subdivided into 'residential with garden' (important
with regard to exposure through vegetable consumption) and 'residential without
garden' (no exposure through vegetable consumption). Moreover, several activities
are covered by more than one land use. Housing, for example, is a prominent activity
in Residential land use, but also occurs in Agricultural land use.
Risks for human health are strongly related to human behaviour. And human
behaviour is highly impacted by the land use and activities taking place on the
site. The degree to which risks are evaluated is mainly a policy decision. Generally
speaking, the protection of human health risks warrants a greater weight in areas
that are meant for human residence. It would be an option to give greater weight to
human health protection in more densely populated areas, possibly with the weight-
ing being proportional to the number of persons impacted, but this rarely occurs in
existing contaminated site management frameworks.
In many countries with a high population density, land use changes in a relatively
short term. The transformation from agricultural land to nature reserves and residen-
tial areas is especially common in many industrialised countries. In Europe, at least
2.8% of the land was subject to change in use between 1990 and 2000 (European
Commission 2009 ) A change in land use has a profound effect on contact possi-
bilities with the soil and on soil properties such as pH, organic matter dynamics
(Römkens 1998 ) and, hence, mobility of contaminants and risks for humans, the
ecosystem, the groundwater and Food Safety.
1.2 Soils and Sites
1.2.1 Soils
1.2.1.1 Definition
According to a broad definition, soil is the upper layer of the earth's crust or, in
geological terms, the exterior weathered part of the earth's rocks. It has been formed
out of rock material by physical, chemical and biological soil-forming processes
over millions of years. Since climatical and geographical conditions varied over this
long span of time, natural soils are typically characterised by a layered structure, that
is, by the presence of soil horizons . According to a more popular definition, soil is
the 'skin of the earth, representing the inheritance of human history'. This metaphor
reflects the vital nature of soil, while at the same time referring to the presence of
historical soil contamination.
Most natural soils have a darker coloured upper layer, the A horizon, with higher
organic matter levels. In many regions of the world, there is a loose organic matter
layer of humus of a few centimetres on top of this A horizon, called an O horizon.
Soil, structured or non-structured, consists of three different phases, namely,
a solid (mineral and organic materials), a liquid ( pore water ), and a gas phase
( soil gas ). Moreover, it contains plant roots and an enormous number of different