Quality of Sediment in Detention Basins–Mapping of the Danish National Road Network

Use of the road infrastructure brings wear of the road surface and vehicles and loss of fuel components. This leads to pollution of the environment near the roads, due to run–off of road surface water to lakes and streams. The two thousand detention basins along the Danish main road network act as delaying basins for sudden large amounts of water and also collect substances which are injorious to the environment, before the water is led to lakes and streams. The Danish Road Directorate has examined the content of substances injorious to the environment in the sediment of 70 basins distributed in the whole country. Analysis of hydrocarbons, PAH, heavy metals and NaCl have been made. The analysis are used to determine the degree of pollution of the sediment in relation to the criteria set out by the Danish Environmental Protection Agency. The results show that at least 90 per cent of the detention basins have sediment which is defined as slightly polluted and at least 61 has sediment which is polluted. These high values are due to the content of hydrocarbons. The second largest source of pollution is nickel and the concentrations show that 20 per cent of the basins have sediment which is polluted by nickel. The highest concentrations of substances injorious to the environment are around Copenhagen and Odense and on the stretch between Kolding and Randers. The content of PAH and heavy metals has been compared to analysis from 38 natural Danish lakes. The analyses shows that there is no marked difference between the measured levels of pollution in detention basins and natural lakes. Hydrocarbons have been compared to two natural lakes and here the difference is very considerable.