What are the scenarios for the present and future situation
In order to carry out a risk-based approach for the megasite of concern, it is necessary to assess the current and future risks to receptors, and possible effect of risk reduction measures. A representation of the sources, pathways and receptors related to the groundwater system at the megasite, as well as prediction of the concentrations and mass fluxes of prevailing contaminants at specified locations over time, requires development of a quantitative (mathematical) model. Such a model allows for appropriate description of groundwater flow and transport of contaminants in groundwater (see figure below). A stepwise approach to modelling is recommended. To go from a comparatively simple model to more complex models requires more effort and data. The model simulations may be carried out in various contexts and with different objectives, in particular:
- to quantitatively summarize the state of knowledge about the megasite groundwater system including fate and transport of contaminants,
- to assess existing risks and to predict future development,
- to predict the effects of different scenarios of mitigating measures
As a result, the decision-support tool is provided for the selection of alternative risk reduction measures or strategies.
This section provides guidance for carrying out contaminant fate and transport modelling at megasites, including interpretation of results and validation. The relevant facts and aspects of modelling are presented in a summarized form, focusing on issues that particularly need to be considered when dealing with megasites. The general presentation of modelling herein is a synthesis of a modelling protocol.
Output
The output of this step is detailed determination and characterization of the contaminants pathways from diverse sources to the receptors within the defined clusters, by means of the fate and transport modelling tools.
