Metal distribution in first flush in highway runoff of one of the busiest motorway junctions in the UK

Although the 'first flush' phenomenon has been extensively studied, there is still a niche remaining for a further contribution to this topic. The work reported in this paper addresses the challenges connected with the first flush from junction 24 of the M1 motorway in the UK. The event monitoring indicated that such factors as ADWP, rainfall intensity plus the catchment cleanliness and the loss of roughness, acting in combination, are the key factors in determining the presence of pollutants in the first flush. In addition, this study has also helped us to better understand the mechanism of iron release due to the presence of anaerobic and aerobic conditions - it showed the greatest proportion of its mass (73.6%), compared to other pollutants, in the first 30% of the runoff volume, which would suggest that the local conditions of the catchment can confound such a simple theory as that of pollutant dilution. The unexpectedly high presence of dissolved iron could be attributed to dissolved organic carbon, humic substances and anaerobic microbial activity. We observed an unexpectedly high proportion of Fe 2+ dis in accumulated highway runoff, which could be attributed to local catchment characteristics.