Source Zone Remediation by ZVI-Clay Soil-Mixing: Reduction of Tetrachloroethene Mass and Mass Discharge at a Danish DNAPL Site

ZVI-Clay soil-mixing is a relatively new in situ remediation technology for remediation of chlorinated dense non-aqueous phase liquids (DNAPLs). The technology combines abiotic degradation (via zero-valent iron, ZVI, addition) and immobilization (via soil mixing and clay addition), whereby both contaminant mass and contaminant mass discharge can be reduced. The technology was tested at a Danish tetrachloroethene (PCE) site. The field sampling consisted of baseline measurements and a 19-month monitoring program (7 sampling campaigns) subsequent to the implementation of ZVI-Clay soil-mixing. The concentrations of chlorinated ethenes were monitored via soil sampling at the source zone and groundwater sampling at a downgradient control plane. The results showed that within one year ZVI-Clay soil-mixing resulted in significant mass depletion of PCE (2-3 orders in magnitude) with ethene as the main degradation product. The down-gradient reduction of contaminant mass discharge was slower; after 19 months a mass discharge reduction of 76 % was obtained for the parent compound PCE, while the overall mass discharge reduction of chlorinated ethenes was 21 %.