Abstract: Infiltration is gaining acceptance, and is even being encouraged, as a practical way to manage storm water on site. To prevent potential groundwater contamination, though, tools are required to predict the potential for contamination due to this infiltration for many site conditions. Infiltration should be encouraged in areas having the least potential for causing groundwater contamination. Factors that influence contamination potential include the pollutant concentration in the runoff directed to the infiltration device (after any necessary pre-treatment) and the ability of the underlying soil to remove the pollutant. This paper presents two levels of modeling for predicting whether groundwater contamination is a concern and whether pre-treatment should be considered.