Transport of stormwater pollutants through a roadside grassed swale

Abstract

Investigations of the pollutant trapping capability of a grassed swale receiving runoff from a road with a traffic intensity of 8,000 vehicles/day were carried out in central Luleå, Sweden. Transport and retention of suspended solids, particles and heavy metals (copper, lead and zinc) were analysed. The sampling was carried out during seven rain events. The results show that once pollutants are trapped in a grassed swale they are not permanently bound to vegetation or soil. A roadside grassed swale may be regarded as a stormwater treatment facility that attenuates the peaks in pollutant loads, without being capable of producing consistently high removal rates.

Keywords:

• Heavy metals
• Pollutants
• Road runoff
• Stormwater
• Suspended solids
• Swale
• Vegetative control

Acknowledgements

This work was supported by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas), the Swedish Council for Building Research (BFR), Swedish Association of Local Authorities (SK), the Swedish Water and Wastewater Association (VA-forsk), Knut and Alice Wallenbergs Foundation, and the local authority of Luleå, which are gratefully acknowledged. The authors are also grateful to Mr Roger Lindfors and Mrs Kerstin Nordqvist for the technical assistance during this project. Finally, the contribution from Professor Jörgen Hanaeus is highly appreciated.