Consolidating simplified risk assessment models for pollutant leaching to and migration across groundwater

Abstract

The major objective of this study is to investigate simplified risk assessment models for pollutant leaching to and migration across groundwater. Data for this study were gathered through bibliographic research and experts’ advice. Three European countries were selected for this investigation: Italy, United Kingdom and Walloon Region. In the first part, the procedures are compared from a theoretical point of view. The Thesis then identifies the tools used by countries and applies them on a synthetic and real case. A sensitivity analysis is performed as well. The cases have highlighted differences in terms of decision-making and shown which parameters mostly affect results. Basing on the results of this research, it can be concluded that all the countries perform Concentration based risk assessment relying on simplified analytical equations and that the way of assessing risk is quite similar. Major differences could be noticed in the choice of factors and relative adjustments for modelling leaching in the vadose zone and in the way to obtain the remedial objectives. Types of solutions for modelling the transport of contaminant across groundwater differ as well. The synthetic case study brings to light some noticeable aspects. Firstly the difficulty in choosing parameters, particularly for the saturated zone, so as to respect the mass balance between saturated and unsaturated condition. Secondly, the fact that some factors, used by countries to simplify the movement of pollutants (i.e. dilution factor), actually have a great influence on results. Therefore, their physical consistency and reliability should be further investigated by comparing results of traditional RA tools with numerical models. Finally, the sensitivity analysis has shown that Mass flux approaches may bring additional contribution to the way the presence of Risk is assessed and that research should evolve in this direction.