Mineral, physical and chemical analysis of the solid matter carried by motorway runoff water

This study forms part of the physical and chemical study of the runoff water from a motorway catchment area in the Hérault region. The distribution of particle sizes and the physical, chemical and mineral characteristics of the sediment contained in the runoff water were analysed for rainfall between February 1993 and March 1994. On average, 90% of the solid matter by weight was in the form of particles smaller than 100 μm. The main organic and metallic constituents of motorway traffic pollution were contained in this sediment. The analysis of the sediment carried by the runoff showed that it contained mineral and organic matter. The contents of this matter were further analysed using X-ray diffraction, thermogravimetry and specific mass measurement. Particles smaller than 50 μm were composed of clays (56%), quartz (15%), chalk (12%), organic matter (9%), feldspars (5%) and dolomite (2%). The specific mass of the particles decreased with the size of the particles and, simultaneously, the percentage of organic matter increased. Excessive lead and zinc contamination was found in both the organic matter and the clay, which formed the largest fraction of particles smaller than 50 μm.