On the basis of the data from the study site and the conceptual model of the ecosystem, it is possible to run models to estimate the contaminant concentrations in all the environmental media; this estimation is necessary in order to subsequently estimate the level of exposure of each receptor to those contaminants. The concentrations estimated in each medium and each receptor are essentially determined by the initial concentrations in the soil, the physico-chemical properties of the contaminants and the defined conceptual model.

Data modelling therefore consists of two distinct steps:

• The modelling of concentrations in the various media
• The modelling of exposure and risks for the various ecological receptors.

These steps constitute the essentials of the conventional process of risk assessment by mathematical modelling. The consideration of biotest results can be added to this approach. In addition to the assessment by mathematical modelling, TerraSys™ can estimate the risks for various ecological receptors based on the results of biotests performed on soil or water samples taken from the study site.

You may use one or the other of the approaches (mathematical modelling and biotests) to assess the risks related to the contamination of a particular site. You may also use TerraSys™ to "integrate" the results of the two approaches, in such a way as to benefit from their complementary aspects. TerraSys™ offers a function for the integration of the two sets of results that accounts for the strengths and weaknesses of each approach, and considers the level of confidence attached to each result.