Innovative in situ treatments of NAPL source zones

Contaminated sites with non-aqueous phase liquid (NAPL) source zones are persistent due to the slow release of the dissolved phase in the generated plume. The groundwater quality criteria for many NAPL chemical compounds are very low, making complete remediation difficult.  Most of the ‘easy’ sites with shallow and accessible source zones were remediated using excavation and off site treatment or landfill, leaving the deep, complex and buried source zones under infrastructure to be treated, which requires in situ remediation technologies. The development of innovative solution involves a multi-scale experimental approach. This involves progressing from batch tests to evaluate compatibility and performance, to 1D column experiments to determine cleaning efficiency and NAPL recovery mechanisms, and finally to 2D and 3D sand tank models to visualize solute propagation and performance, prior to a field pilot test and the full implementation of the technology. This paper presents and discusses some examples of thermal (e.g. electrical resistivity heating and thermal conduction heating), chemical (e.g. surfactant, chemical oxidation and foam) and biological (e.g. enzyme) treatments, showing their limitations and the challenges to be overcome.