Assessment of metal retention in newly constructed highway embankments.

Newly constructed embankments should provide both a specific bearing capacity to enable trafficability in emergency cases and a sufficient pollutant retention capacity to protect the groundwater. A number of lysimeters were installed along the A115 highway to determine total and dissolved metal concentrations in road runoff and in the soil solution of newly constructed embankments. Dissolved concentrations in soil solution of the embankments did not exceed the trigger values of the German legislation. Depending on the metal, total concentrations in soil solution were more than twice as high as dissolved concentrations. The high infiltration rates lead to increased groundwater recharge beneath the embankments (up to 4100 mm a-1). Although metal concentrations were not problematic from the legislators' point of view, the elevated infiltration rates beside the road facilitated the transfer of high metal loads into deeper soil layers and potentially into the groundwater as well.

Metal leaching in a highway embankment on field and laboratory scale.

Increasing worldwide motor vehicle traffic leads to the question of the possible environmental consequences. This paper aims to analyse metal leaching in a highway embankment using both field and laboratory experiments. Soil, soil solution and road runoff were collected along one of the oldest highways in the world to characterize leaching of the metals Cd, Cr, Cu, Ni, Pb and Zn. Batch, column and adsorption experiments were carried out to study the reliability and transferability of laboratory approaches. Depending on the element, the ratio of particle-bound metals in road runoff varied between 15-90%. Metal levels in embankment soils were significantly higher compared to a reference site in a forest at 800 m distance (up a factor of 30). High metal concentrations in soil solution at 50 cm soil depth were not a direct result of road runoff but rather of elevated concentrations in the soil matrix. The use of batch S4 elution was found to be the best overall laboratory method to predict soil solution concentrations in field. Adsorption experiments showed a relative increase in retention capacity in roadside soil of up to a factor of 20 after nearly 100 years of operation. The input of alkaline dust and organic carbon into roadside soils increases its retention capacity in the long term.

Metals in European roadside soils and soil solution--a review.

This review provides a summary of studies analysing metal concentrations in soils and soil solution at European roadsides. The data collected during 27 studies covering a total of 64 sites across a number of European countries were summarised. Highest median values of Cr, Cu, Ni, Pb, and Zn were determined in the top soil layer at the first 5 m beside the road. Generally, the influence of traffic on soil contamination decreased with increasing soil depth and distance to the road. The concentration patterns of metals in soil solution were independent from concentrations in the soil matrix. At 10-m distance, elevated soil metal concentrations, low pH, and low percolation rates led to high solute concentrations. Directly beside the road, high percolation rates lead to high annual loadings although solute concentrations are comparatively low. These loadings might be problematic, especially in regions with acidic sandy soils and a high groundwater table.