Site-Specific Ecological Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 711

Table 15.3 Scheme for supporting ERA with respect to determining the urgency of remediation
at seriously contaminated sites in the Netherlands (VROM 2008 , modified and currently under
discussion). Depending on the land use, it is not necessary to take measures when the horizontal
dimensions of the unpaved contaminated area within the contour for the Toxic Pressure (TP) is
smaller than indicated. Two levels for the TP are used, i.e. TP

= 0.2 or TP = 0.5

Unpaved surface area
contamination
(TP MMec50 ∗ >0.2)

Unpaved surface area
contamination
(TP MMec50 ∗ >0.5) Land use

< 500 m 2 <50m 2

Sensitive:
nature (including Ecological Main
Structure and Natura 2000 areas)

< 5.000 m 2 < 500 m 2

Intermediate:
agriculture, (vegetable) garden, green
areas with 'nature values' ∗∗

< 50.000 m 2 < 5.000 m 2 Insensitive:

other green area's, strips in build areas,
infrastructure and industry

∗ TP MMec50 is the Toxic Pressure, which is calculated from the mixture of contaminants in soil
samples (Box 15.1 ). The TP is calculated on the basis of total concentrations in the samples, and
related to EC50 data from the literature and a mixed model for mixture effects (De Zwart and
Posthuma 2005 ). Background concentrations of substances are subtracted from the soil sample
concentrations. All concentrations are corrected for a standard soil (see Swartjes 2010). More
details about the calculations can be found in Rutgers et al. ( 2008b ).
∗∗ Outside the Ecological Main Structure and Natura 2000 areas 'nature values' are considered
relevant, unless particularly stated in the petition on the land use.

about the land management regarding the contamination. In these cases, additional
effort via application of the Triad approach in a subsequent tier to further improving
ERA is recommended. For application of the Triad practical guidance is available
(Jensen and Mesman 2006 ;Mesmanetal. 2007 ; Rutgers and Den Besten 2005 ).

15.6.2 Examples of the Lines of Evidence in the Dutch
Remediation Criterion

In the Netherlands, a practical Triad approach has been developed (Mesman et al.
2007 ). In Box 15.1 some examples of methods and calculation tools are presented.
The three lines of evidence are described below, together with the collection of basic
tools recommended for this tier of the Remediation Criterion (VROM 2008 ):

1. Chemistry: Model and parameters are equivalent to those at tier 2 of the
Remediation Criterion (Rutgers et al. 2008b ;VROM 2008 ). It consists of a cal-
culation of the Toxic Pressure from the mixture of contaminants in soil samples
from the contaminated site. The two-step mixed-model approach for mixture tox-
icity is used, combining concentration-additivity and response-additivity models
(De Zwart and Posthuma 2005 ). In order to arrive at a number for the Toxic