In situ remediation of an Hexavalent Chromium contaminated site uin Milan area (Italy) by soil flushing and geochemical fixation

A soil flushing and geochemical fixation treatment of soil and groundwater contaminated with Hexavalent Chromium in an industrial site in Brugherio (Milan, Italy) is described. The contamination in soil and groundwater, that lately reached its maximum concentrations of 4.6 g/kg and 4.5 mg/l respectively, originated in 7987 due to poor storage and improper disposal practices in a chromium plating facility, with a total Cr(Vi) leakage of about 250 kg. This event resulted in a contamination pIume of nearly 6.5 km downgradient from the site, located in the upper aquifer characterized by gravel - sandy deposits and a water table depth of 20 - 25 m. Design solutions supported both by experimental tests during site assessment and site investigation phases and groundwater flow and contaminant transport modeling, were applied; a dual remediation system (soil flushing and geochemical fixation), representing the first application in Italy, was then implemented. This system achieved the clean up goals with good performances in terms of remediation time and capital and operating & maintenance costs and it was recognized as a valid alternative approach, both from a technical and an economical point of view, in substitution of digging, removal and authorized dispose! of contaminated soil.