Use of hydrogeological and geochemical methods to investigate the origin and fate of vinyl chloride in groundwater in an urban environment, Ferrara, Italy.

Vinyl chloride (VC) groundwater contamination around the city of Ferrara, Italy, is rather widespread and has created a serious environmental problem in this highly urbanized region. The paper discusses recent data derived from a geochemical and isotopic fingerprinting study carried out at the Pandora site, which is characterized by the existence of a long VC plume, and at the Caretti site where high concentrations of chlorinated compounds, including VC, occur. Data was also collected at an unconfined aquifer under¬neath a major petrochemical plant. The isotopes data show that the unusual negative δ13C values observed in the VC at both sites (Pandora –43 and –65‰; Caretti: –62 and –72‰) could not be attributed to reductive dechlorination of manufactured primary PCE or TCE. Unusual negative δ13C values for PCE and TCE also characterise the impacted aquifer beneath the petrochemical plant and the Caretti site. Based on the industrial history of the region, which includes production of PVC and chloromethanes (ClM), it is postulated that contamination in the Ferrara region is linked to wastes originating from the production of chloromethanes. The primary organic compound used in ClM production is methane, which is strongly depleted in 13C similar to the values observed in VC, PCE and TCE at the investigated sites. It is also postulated that the contamination is linked to dumping of industrial waste in the abandoned lagoons used by the sugar industry and in clay pits associated with the clay industry.