Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 19

concept 'contaminated site', including the soil (upper soil and aquifer) underneath
the surface and the human occupation on the surface.
The focus of this topic is on the threats for the four major protection targets;
these are human health, the ecosystem, the groundwater and Food Safety, as related
to contaminants present in the soil or the groundwater. From this perspective, the
extent of the earth's crust that is relevant in the context of this topic is limited to
that part that impacts human health and the ecosystem, and the groundwater that is
within human reach. More concretely, this primarily relates to the upper, unsaturated
soil layer and the first tens meters of the groundwater layer. To a lesser extent, those
groundwater layers will be considered from which groundwater is extracted (up to
several hundreds of meters). Since this topic relates to compounds that have adverse
effects, these compounds are called contaminants throughout the topic.
Two types of contaminated sites exist with regard to the extent and shape of the
location that is contaminated, namely, diffuse and local contaminated sites. This
extent and shape of a contaminated site is often dependent on the type of source that
is responsible for the contamination. Generally speaking, atmospheric deposition
and, to a lesser extent, large scale agricultural activities lead to diffuse contamina-
tion. Diffuse contaminated sites caused by atmospheric deposition are characterised
by large contaminated areas. Often the contaminant concentration decreases along
regular circles from the source, for example, in the case of lead smelters (e.g.,
Filzek et al. ( 2004 ), who measured the metal concentrations in soil along a transect
from a smelter at Avonmouth, UK), where the concentration contours are possi-
bly stretched according to the wind direction. Diffuse contaminated sites caused by
agricultural practices generally are characterised by a relatively homogeneous con-
tamination pattern. One specific version of diffuse contaminated sites is known as
ribbon contaminations , for example, along roads or railroad tracks.
Locally contaminated sites vary in size from a small back yard of a few square
metres to an industrial site of several tens of thousands of square metres. These
locally contaminated sites generally are characterised by a heterogeneous contam-
ination pattern, often with one or more cores (hotspots) of contamination, related
to the source of the contamination. In many cases, the larger locally contaminated
sites can be considered as a collection of smaller locally contaminated sites. There
is no absolute definition of diffuse or local contaminated sites. Some sites have char-
acteristics of diffuse and local contaminated sites combined, for example, in large
diffusively contaminated sites with contaminant hotspots.
This topic deals with contaminated sites, either diffusely contaminated or locally
contaminated. However, since most chapters of this topic deal with Risk Assessment
tools that can be used for any type of contaminated site, this distinction is not always
relevant.
In principle, the topic does not implicitly deal with agriculturally managed sites.
The reason for this is that agricultural activities often lead to a continuous supply of
contaminants to the soil as part of agricultural business. This means that managing
the contaminant status of agricultural sites, and the related risks, is a matter of bal-
ancing the inputs and outputs of contaminants. Pesticide application, for example,
is focused on administering the applications needed for the goal to be reached (for