A NEW TECHNOLOGY FOR THE REMEDIATION OF RESIDUAL DNAPL SOURCES: RESULTS FROM THE FIRST FULL SCALE TEST

Abstract

A new technology for remediation of Dense Non Aqueous Phase Liquid (DNAPL) aged source zone is reported in this study. The objective of the remediation is to enhance in situ bioremediation (ISB) by coupling Groundwater Circulation Wells (GCWs) with an electron donor continuous production system. The technology has been verified through a pilot test carried out in an operative industrial site located at north Italy, heavily contaminated by Chlorinated Aliphatic Hydrocarbons (CAHs). Site characterization confirmed a complex hydrogeological situation with the occurrence of active residual sources in low permeability layers. On the basis of the site specific geological heterogeneity, a three-screened GCW has been designed and installed at the site to create an in situ vertical groundwater circulation cells by extracting groundwater from the aquifer through the intermediate and lower screens extended, respectively, from 15 to 19 m and from 22 to 26 m bgs (below the ground surface) and reinjecting it through the upper screen extended from 8 to 12 m bgs. Before discharging into the aquifer, the extracted groundwater is circulated to an external treatment system composed of a sand filter and two reactors; one reactor was filled with a biodegradable polymer (poly-hydroxy-butyrrate, PHB) whose fermentation continuously produce dissolved electron donors and the other one with zero-valent iron (ZVI) (for the removal of the extracted chlorinated solvents). Results from the field test have clearly demonstrated the significant mobilization of contaminant from the low permeability zone in comparison with traditional technologies and the possibility to effectively distribute electron donors enhancing in situ natural attenuation mechanisms based on biological reductive dechlorination.