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In situ mechanical-pneumatic clean-up of contaminated low permeability soils

At many contaminated sites the estimated remediation time for the clean-up is much longer than originally expected. One of the reasons for this behaviour is the subsurface heterogeneity. One way to overcome this limitation is through the new method of in situ mechanical soil mixing. The release rates before and after the mechanical treatment were determined by a series of large-scale laboratory column experiments. The data obtained from these experiments show that in situ mechanical mixing in the saturated zone cannot be recommended. However, in situ mechanical mixing in the unsaturated zone combined with soil vapour extraction (mechanical-pneumatic clean-up) increases the flux of VOC (volatile organic compounds) extensively due to high flow rates of air and thus leads to very short remediation times of less than an hour. The remediation times depend on the diffusion rate constant D a /a 2 which is strongly influenced by the mechanical-pneumatic treatment.