Chemical and Physical Changes in the Subsoil of Three Waste Landfills

Drilling through two industrial and one mainly domestic waste landfill offered the opportunity to study the changes and migration of leachates in clayey bedrocks. The mineralogical composition and spectrum of clay minerals of the bedrocks varied considerably between the three sites, but, with one exception, no mineralogical changes caused by the leachate were observed. In this one case the clay minerals were destroyed in the uppermost 5 cm by the effects of the highly concentrated leachate of the industrial waste during 25 years. Below this depth the scanning electron microscope investigations showed no disturbances of the microtexture of the bedrock that might have caused higher permeabilities. Heavy metals like copper and zinc are immobilized in the uppermost strata. Water soluble chloride diffusively migrates through the clayey bedrocks. The diffusion constants calculated from the measured profiles indicate retardation mechanisms that hamper the migration of soluble compounds by factors of 20 to 60. The permeability of natural clayey bedrocks does not seem to be affected by the leachates.