EPP(Expanded Polypropylene) media with a large surface area was developed to treat the first flush of storm water from motorway. A series of studies have been carried out concerning the main mechanism of physical characteristics with the filtration and adsorption of EPP media in EcoTank system in order to evaluate the performance risk for treating trace metals (Cd, Cr, Cu, Pb and Zn) under uncertainty. In view of quantitative and qualitative risk analysis, this study assesses the uncertainty analysis involved in predicting of treating heavy metals from road runoff using an EcoTank system. Results of treatment performance estimation after the treatment of trace metals using an uncertainty analysis were 50.0.% probability (class 3; moderate) for Cd, 52.0% probability (class 4; high) of Cr, 47.1% probability (class 3; moderate) for Cu, 44.4% probability (class 3; moderate) for Pb and 51.2% probability (class 4; high) for Zn, respectively. The performance risk values of all the heavy metals satisfied the acceptable criteria.