Ecological Risk Assessment of Diffuse and Local Soil Contamination Using Species Sensitivity Distributions - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 679

14.14.4.2 Approach
The first steps that need be made according to the current Dutch soil appraisal
approach are to define land uses and land use zones, and to compile contamina-
tion levels for each zone. An example of the different land uses within the area of a
municipality (Gouda, the Netherlands) is given in Fig. 14.17 (top).
A municipality can thus discriminate between different land uses and different
soil qualities, and check whether the current or future land use is “at risk” given
the contamination levels present or expected. If risks appear, due to a mismatch of
soil use and soil contamination class, the responsible authorities can start a process
to alter land use or to reduce risks in other ways. The Risk Toolbox supports this
evaluation, since potential mixture effects are accounted for in the assignment of
soil quality classes.
After the soil use zonation map is made and compared to soil contamination class
boundaries (concentrations), land use and soil contamination may be consistent (i.e.,
actual land use is not hampered by exceedances of land use related risk limits) or not.
In the latter case, the exceedances of the soil-class limits does not yet specify
which exposure scenarios would result in acceptable risk. This can then be fur-
ther investigated with the toolbox and subsequent Risk Management of the existing
situation.
An additional step is triggered when there is a need for soil transfer, such as dur-
ing building activities. To support soil transfer, a soil transfer exploration matrix is
made, looking at sources and possible sinks of soils in an area. Soils can be trans-
ferred to a site in the same quality class (e.g., “residential”) or to a site with a higher
permissible contamination (e.g., “industry”), so that there is no increase in risk (as
could, for example, occur when transferring soil from a site in the class “Industry”
to a site in the class “Residential”).
14.14.4.3 Conventional Risk Assessment Results
The Risk Toolbox is of help to local soil managers if there is concern about current
use of a soil zone in relation to exceedances of the soil quality standards. In that
case, the Risk Toolbox provides insight into the local magnitude and type of risk,
such as in Fig. 14.17 (bottom) using a Hazard Index approach.
Thereafter, the toolbox was used to quantify the local chronic toxic pressure
on soil biota in a soil use with moderate ecological protection (M), in the soil
use zone “Residential”. The toxic pressure of the local mixture was calculated as
21% (msPAF-NOEC). This implies that the mixture exposure probably results in
less protection than the 95%-protection criterion. Such a toxic pressure level may
be considered by local authorities as not extremely serious for a residential area
(msPAF-NOEC does not necessarily imply species loss), for example because the
level is at least lower than the 50%-toxic pressure level used earlier in the remedia-
tion policies (the HC50 used as trigger implied a chosen PAF of 50% or higher for
remediation, per compound).