Field test: injection of a new reactant and geophysical monitoring of the remediation

This work presents the results of a pilot field test concerning the remediation of a polluted site by chlorinated solvents located in Northern Italy. A physic-chemical, stratigraphic, hydrogeologic and hydraulic characterization of the site outlined a rather complex context. Vinyl chloride was identified as the secondary pollutant of main interest, proving the occurrence of natural degradation phenomena, therefore enhanced bioremediation was chosen as the technical solution to be performed. The site was prepared for a field pilot test: Hydrogen Release Compound (HRC-X, Regenesis) was injected, and the effects on pollutants’ concentrations and on groundwater geochemical properties were evaluated for about five months after the injection, by means of the analysis of physic-chemical parameters (pH, electric conductivity, temperature, oxidation-reduction potential were analyzed on site, while pollutants’ concentrations and other parameters were analyzed off site); a geophysical monitoring was also performed by means of cross-hole electric tomography measures. The results of the monitoring activity performed after the field pilot test outlined that HRC was quickly transported downstream by groundwater flow and that the second aquifer layer, located at a 13-14 m depth, was the mostly interested by the degradation activity of the halogenated pollutants having the higher number of chlorines; this issue was witnessed by a relevant decrease of oxidation-reduction potential, a sharp increase of the electrical resistivity, and an enhancement of the amount of the less chlorinated pollutants, particularly vinyl chloride.