Experimental assessment of soil and groundwater contamination from two old infiltration systems for road run-off in Switzerland

Surface and sub-surface infiltration systems for road run-off at two sites in Switzerland were investigated by sampling and analysing the run-off sludge and soil found in the systems. The infiltration systems were between 12 and 45 years old. Measured pollutant parameters included the heavy metals Cr, Co, Ni, Cu, Zn, Cd and Pb, a number of polycyclic aromatic hydrocarbons (PAH) and adsorbed organically bound halogens (AOX). Total concentrations were measured to assess the extent of soil contamination. Further, metal concentrations were measured in equilibrated aqueous extracts to simulate naturally occurring concentrations in percolating water. In the infiltration systems the pollutant concentrations decreased rapidly to background levels within depths less than 1.5 m. The potential for groundwater contamination from infiltration of road run-off appears to be limited, but soil and run-off sludge found in infiltration systems can be heavily contaminated. Noteworthy, the run-off sludge itself plays an important role as pollutant source and sorbent.