Underground sedimentation systems for treatment of highway runoff in dense city areas

Paper in proceeding, 2005

The pollutant characterization, removal efficiency and function of a newly constructed underground sedimentation system for treatment of highway runoff have been investigated. Results from flow weighted sampling, during eight consecutive storm events, show a high inflow of heavy metals and carcinogenic PAHs. The concentrations of carcinogenic PAHs in the inlet water exceeded the Swedish guideline values for polluted groundwater at petrol stations. The relatively high amounts of specific PAHs such as pyrene, fluoranthene, chrysene, and benzo(g,h,i)perylene, indicate road asphalt, vehicle exhaust and tyre rubber as important sources of pollution. In the outlet water, the concentrations of all PAHs were effectively reduced and far below the guideline limits. The heavy metals found in highest concentration in the inlet water were zinc, copper, chromium, lead, cadmium and nickel. They all, except nickel, exceeded the Swedish quality criteria values for watercourses, even in the outlet water to the urban river. The average pollutant removal efficiencies of the treatment system were for TSS ~ 30 %, VSS ~ 25 %, heavy metals 15?35 % and for PAHs ~ 30 %. The results also show that the efficiency of the sedimentation construction could be improved by optimisation of operational conditions such as detention times.