Design of a sand filter for highway runoff in the north of Spain

Urban and highway runoff has negative environmental and ecological effects on the waters that receive it. Highway runoff mobilises heavy metal elements and suspended solids from atmospheric deposition and traffic, as well as road degradation and maintenance. A pilot sand filter is designed to reduce metals, hydrocarbons and suspended solids from a highway reach in Fene, Spain. This unit filters a percentage of highway runoff, reducing the mobilised loads of pollutants through filtration and sorption. A monitoring programme is developed to characterise runoff pollution of the pilot catchment. Runoff is found to be heavily polluted with sediments, high chemical oxygen demand, total phosphorus, copper and zinc. Field data are also used to develop a calibrated hydraulic model of the catchment with the storm water management model. From the long-term simulations using this model, the filtration device is designed for an average spill frequency of about 20 events per year and to capture and treat approximately 90% of the average annual stormwater runoff.