Michel Legret

Comparison of the hydraulic behaviour and the quality of highway runoff water according to the type of pavement

This paper presents the results of an experimental investigation aimed at determining the impact of the type of pavement, whether conventional or porous, on the hydraulic behaviour and on the quality of runoff water. Data obtained from a French highway both before and after the replacement of a conventional asphalt by a porous asphalt are compared. Statistical tests have been used to evaluate the significance of the differences detected. Firstly, the differences in hydrological behaviour between the two types of pavement is highlighted (retardant effect on the evacuation of water into the outlet, peak flow attenuation, mitigation of splashing by the pervious pavement). Secondly, the impact on water quality is investigated. The retention of particulate pollution by the porous pavement, which acts as a filter, is clearly demonstrated. This study also shows the probable impact of the type of pavement on the pollutant content in a dissolved form.

Heavy metal pollution of road dust and roadside soil near a major rural highway.

The concentrations of lead, copper, cadmium, zinc, nickel and chromium were measured in road dust and roadside soils from a French major highway. The profiles of total levels in the soil as a function of distance from the road edge and as a function of depth were investigated. Lead, zinc, copper and, to a lesser extent, cadmium contamination were found in samples taken on the surface and in the immediate vicinity of the road. The observed concentrations decreased rapidly with distance and depth. Soil samples appeared to exhibit little nickel and chromium pollution. The geochemical phases on which heavy metals (lead, copper, zinc, cadmium and chromium) were fixed preferentially, as well as the potential mobility of the different metals under certain physical and chemical conditions were evaluated. Sequential extractions and single extractions with different reagents were performed. Chromium, which was present mostly in residual form, was mainly of natural origin in the studied samples and was not highly mobilisable. Cadmium was the most easily exchangeable element in case of variations in the physical and chemical conditions but the quantities involved remained small. Lead and copper did not appear to be highly mobile. Only drastic conditions, such as those that may be produced by accidental spillage of a chemical product (acid or complexing agent), mobilised them quantitatively. A significant risk of mobilisation was to be feared only in the case of zinc, which is very sensitive to acid pH.

Size Fractionation of Heavy Metals in Highway Runoff Waters

Highway runoff waters may contain pollutants that have accumulated on the carriageway. Numerous field surveys have demonstrated that heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) are common pollutants in highway runoff waters that degrade the quality of natural water bodies [1–6]. These hazardous pollutants have been found to be attached to particles, especially finer particles than 100 μm, usually quantified by dissolved, suspended and settleable solids measurements [7]. Clay minerals, very fine silts, metallic oxy-hydroxides and organic matter were identified as main components of the composite particulate matter [8, 9]. The knowledge of partitioning of trace metals between the different solids fractions is crucial for stormwater management. The pollutant size distribution determines the efficiency of runoff water treatment by settling in detention basins. Moreover, the toxicity and bioavailability metal characteristics also depend on the speciation of pollutants that could be discharged into natural water bodies. Partitioning of pollutants is also challenging nowadays due to issues of colloid-mediated transfer of heavy metals, as it was already shown for roadside soils impacted by runoff waters [10].

Evaluation of platinum distribution between different soil components

PurposeMore attention has been given to the determination of background levels of platinum group element (PGE) in an urban environment. But, few studies have been conducted for its environmental behaviour. The necessity to understand the PGE behaviour in environment increases due to the increase in platinum (Pt) emissions. The aim of the study is to evaluate the adsorption and the distribution of Pt within soil and sediment components. This study investigated the Pt adsorption on kaolinite, hematite and humic acid.Materials and methodsA batch experiment was used to determine sorption of Pt. The experiments were carried out on the three solids and on two mixtures of iron oxide and kaolinite, with two ratios 25:75 and 75:25. An elemental distribution of Pt was determined on the mixtures iron oxide–kaolinite by micro-X-ray fluorescence.Results and discussionThe highest concentrations of Pt were found on kaolinite, followed by hematite and humic acid. Kaolinite exhibited the highest adsorption capacity. The sorption capacity of both mixtures was lower than that of kaolinite and iron oxide. Moreover, the shape of isotherms, for both mixtures, tends towards that of kaolinite. The elemental distribution maps of mixtures showed, for both ratios, a high enrichment of kaolinite with Pt opposite to a slight enrichment of hematite.ConclusionsThe results showed that Pt is adsorbed mainly on kaolinite, which suggests that Pt was mainly associated with clay in soil. The results allowed the evaluation of the impact of the matrix of soil or sediment on the ability to retain or promote Pt dispersion in an urban environment.