Monitoring pollutants in highway runoff

Highway surface runoff discharges may contain pollutants that have accumulated on the carriageway, particularly following periods of dry weather. The Highways Agency, in association with the Environment Agency, commissioned a 5‐year study in 1997 to collect data to improve the understanding of pollutants in highway runoff and the treatment efficiency of drainage systems. The study involved the monitoring of nonurban highway drainage at six sites, each for a minimum of 1 year. The results have been used to identify ranges of pollutant concentrations in highway runoff, relationships between runoff concentrations/loads and both highway and environmental factors, drainage system treatment efficiencies, and impacts on receiving waters. This paper describes the methods used for runoff monitoring, the results obtained to characterise pollutants in highway runoff, and the measured pollutant removal efficiency of a number of drainage system types.