Verification of laboratory–field leaching behavior of coal fly ash and MSWI bottom ash as a road base material

A theoretical relationship between the desired level of protection of soil and groundwater and the results of laboratory leaching tests forms the basis for the Dutch Building Materials Decree (BMD). The assumptions made in this Decree were verified by field measurements after about 10 years of field exposure at two locations where well-characterized secondary raw materials have been used in road construction. The results of release predictions based on laboratory leaching tests have been compared with release estimates derived from concentration decrease in the building material, from soil profile analysis (including analysis of collected percolation water), and leaching of already exposed material. A reasonable to good agreement between prediction and measured release in the field has been observed, in spite of sometimes-large uncertainties in field release estimates. Modifications in the release prediction are proposed to account for observed discrepancies between lab and field for specific constitutents or specific conditions, such as the degree of water saturation in soil.