Stormwater runoff quality on an urban highway in South Africa

Roadway sediment and stormwater runoff were sampled from a 15 km section of the R300 freeway located in the greater Cape Town area, South Africa. Grab samples were collected over a four-month period in 2016 and analysed for metals, hydrocarbons and nutrients. The metal concentration profiles were similar in sediment and runoff samples. The primary pollutants identified in the highway runoff were aluminium, copper, lead, manganese, nitrogen, phosphorus, zinc, total suspended solids (TSS), and oil and grease. The concentrations of each of these elements, barring lead, exceeded the national effluent water quality guidelines. Large volumes of macro pollutants such as cigarettes, plastic and packaging were also observed. The results of this research indicate that Sustainable Drainage Systems (SuDS) should be used in conjunction with highways, particularly where runoff may influence a sensitive or valuable aquatic ecosystem, as it can be a significant non-point source of pollution.