Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 49

between acceptable and unacceptable cases of soil contamination. Since the late
1980s, risk-based Soil Quality Standards have been derived in several developed
countries.
Several types of Soil Quality Standard exist, for different purposes. Carlon and
Swartjes ( 2007b ) distinguished three classes of Soil Quality Standards. The first
class of Soil Quality Standards, with the most stringent values, represents the upper
limit for long-term sustainable soil quality, appropriate for prevention purposes or
as remediation objectives. The second class, with the highest values, triggers actions
such as either a more detailed Risk Assessment or Risk Management actions (e.g.,
remediation) when exceeded, and are used for curative purposes, that is, for sup-
porting the risk appraisal for existing contaminated sites. The third class is an
intermediate class, and supports further research actions such as the performance
of more detailed soil sampling.
As was mentioned in Section 1.7.1.3 , Soil Quality Standards are applied to a
whole series of contaminated sites. Therefore, a generic exposure scenario needs
to be defined for a hypothetical site. Generally speaking, such a generic sce-
nario either relates to standard assumptions, as for frequently found contaminated
sites, or to conservative assumptions. The latter must certainly be the case when
'false negatives' (the incorrect assumption that there is no unacceptable risk) get
a higher political negative weight than 'false positives' (the incorrect assumption
that there is an unacceptable risk). Also in a case where Soil Quality Standards
are used as a trigger for possible site-specific Risk Assessments, generic sce-
narios as basis for the Soil Quality Standards need to be based on conservative
assumptions.
A variation on generic Soil Quality Standards relates to 'land use-specific Soil
Quality Standards'. As the term says, it refers to several Soil Quality Standards
for different land uses, for each specific contaminant. One advantage of human
health-based land use-specific Soil Quality Standards is that more realistic exposure
scenarios for the respective land uses can be used. An advantage of ecologically
based land use-specific Soil Quality Standards is that a more appropriate level of
ecological protection can be chosen for the respective land uses. The disadvantage of
land use-specific Soil Quality Standards is that the derivation process is much more
intensive, since a series of Soil Quality Standards must be derived for each con-
taminant. The use of land use-specific values in practice is less convenient, since a
choice needs to be made for each site as to which land use is appropriate. Moreover,
the application of land use-specific Soil Quality Standards may give a misleading
idea of accuracy.
Examples of human health-based Soil Quality Standards are given in Hristov
et al. ( 2005 )for Human Health Soil Screening Levels (CHHSSL) in California,
USA, and in DEFRA and EA ( 2002 )for Soil Guideline Values for metals in the
UK. Examples of ecologically based Soil Quality Standards are given in Canadian
Council of Ministers of the Environment ( 1999 ) for Canada, and in National
Environmental Protection Council ( 2003 ) for Australia. An example of combined
(human health and ecological based) Soil Quality Standards is given in Ministry of
VROM ( 2008 ) for the Netherlands.