Risk assessment for groundwater: comparison of transient and stationary approach for modelling contaminant leaching in the vadose zone

In recent Italian regulations an appropriate risk assessment has become an essential step in the remediation procedure of contaminated sites. If groundwater must be considered as receptor, the risk assessment will require analysis of leaching from the contaminant source in unsaturated soil into the groundwater. Transport analysis is usually carried out by means of analytical models implemented in calculation softwares. In this study three different analytical models of leaching are compared with reference to a given site geometry and three different contaminant types. The first model is suggested by the Italian regulatory agency (ISPRA) and consists in a simple soil-water partitioning, soil attenuation and dilution. The second is the leaching model implemented by the software RISC4. The third model simulates 1-D flow and solute transport across the vadose zone, considers dilution with groundwater and allows to extend the simulation to an unlimited time span.Illustrative examples are given for the three model contaminants and for the given site geometry