The contribution of highway surfaces to urban stormwater sediments and metal loadings

Abstract A 0.05 ha highway subcatchment located within a larger 243 ha separately sewered residential estate in NW London has been investigated to evaluate the relative pollutant contribution of highway surfaces to total urban runoff discharges. Mass balances for both solid and soluble metal loadings for the subcatchment are ‘scaled-up’ to estimate the potential impact of rooftop, road surface and roadside gullypots on stormwater loadings discharged to the receiving stream from the parent catchment. The scaling-up procedure predicts a 46%, 78%, 47% and 13% contribution of total Cd, Cu, Pb and Zn loadings respectively from road runoff with ratios of soluble to insoluble metal being 4.0, 1.8, 0.2 and 3.0 respectively for these metals. The analysis confirms the importance of belowground, in-pipe processes in modifying the inherent geochemical characteristics of road runoff quality as well as highlighting the potential deleterious effect of uncontrolled highway discharges on receiving stream quality.