Beoordelingssystematiek bodemkwaliteit ten behoeve van bouwvergunningsaanvragen. Deel III. Methodiek ter bepaling van het actuele risico voor het ecosysteem

In the framework of the Dutch "Woningwet" (housing law) an approach is developed with the aim of assessing ecological risks of contaminated land. This approach is part of a more general decision support system, on which the assessment of soil quality in granting a building permit for a parcel will be based. Theoretical backgrounds of ecological risk assessment of contaminated sites are given. Within the context of the housing law there are very important limitations with respect to data availability and time available for decision making. This restricts very strongly the possibilities for ecological risk assessment of building parcels and forces to make a choice for a very pragmatic approach. Consequently, one is compelled to accept considerable sources of uncertainty. The proposed approach consists of three elements that are integrated in an assessment scheme. (1) The amount of pollution induced toxic stress on the ecosystem. This is estimated by adding pollution units of the individual contaminating chemicals. A pollution unit consists of the soil concentration of a chemical divided by its Hazardous Concentration 50% (HC50). (2) An estimate of exposure judged by the land-use type of the parcel. (3) An estimate of ecological accessibility based on the land-use in the neighbourhood of the parcel. The assessment scheme is based on the supposition that higher pollution induced stress is acceptable in situations with low chance of exposure and scarce ecological accessibility. Risk levels in this scheme should be given by policy makers because reliable technical and scientific arguments are lacking. Uncertainties of the proposed method are discussed and possibilities are given how improvements in reliability can be made