Re-cycling of remediated soil – Evaluation of leaching tests as tools for characterization

In Sweden, leaching tests with deionized water (D.W.) are utilized in risk assessment of materials entering landfills, but implementation of these results to evaluate the risk of spreading of pollutants in the environment is difficult. One problem is that most leaching procedures only consider heavy metals release, whereas organic pollutants are left out. The aim of the present study was to assess the possible pollutant mitigation in four remediated soils, three with heavy metals and one with polycyclic aromatic hydrocarbons (PAH) contamination. The mitigation was evaluated by standardized batch and column leaching tests utilizing three different leaching solutions: D.W., a weak ionic solution (0.001 M CaCl2) and an artificially made soil water (ASW). In general, batch leaching tests implied larger contaminant removal than column leaching test, possibly due to the more rough treatment of the soil particles, and guidelines would at times be exceeded by the batch leaching test but not by column leaching tests. Utilization of CaCl2 was found to release less heavy metal than D.W., whereas the metals mobilized by ASW were removed from solution by the filtration of soil leachates. Low molecular weight PAH was most efficiently mobilized by CaCl2, while D.W. worked better for high molecular weight PAH. Despite very low initial PAH-concentrations, tap- and groundwater criteria were exceeded by all leaching solutions.