The issue of chlorinated solvents in Europe: the case of the Caretti site

Many urban areas in Europe denote a widespread occurrence in groundwater of chlorinated solvents, in particular Tetrachloroethylene (PCE) and Trichloroethylene (TCE). Chlorinated solvents are a large family of compounds that are widely used in several industries all over Europe. They are often spilled in the ground as Dense Non-Aqueous Phase Liquids (DNAPLs) and typically cause strong and persistent environmental contamination. During the last few decades, the intense sprawling of urban territories has caused a large increase in the potential for human exposure to the presence of PCE and TCE in groundwater. The frequent overlap between industrial, residential and agricultural areas causes, in many instances, a conflict between former and latter land-uses (e.g. development of residential neighbourhoods over dismissed industrial areas or old dumps), with new issues arising with land use planning. The Caretti site (Ferrara, northern Italy) is an urban setting investigated within the GENESIS project and represents an example of a recently developed residential area that is strongly impacted by a mixture of chlorinated solvents (mainly PCE and TCE). This residential area was built on a former suburban area, devoted in the past to agricultural and clay-quarrying activities. Two dumps for domestic wastes were located at the site, which were filled, during ’60 and ’70, also with industrial wastes. The three shallower sandy aquifers of the local alluvial multi-layered hydrogeological system were investigated by means of a variety of approaches, including classic hydrogeological methods as well as detailed vertical profiling methods including depth-discrete sampling of continuous cores and multi-level groundwater sampling. The GENESIS project investigation demonstrated, through a carbon-stable isotopic fingerprinting approach, that the chlorinated pitches in the local dumps were derived from production at the local petrochemical plant (Nijenhuis et al., 2013). DNAPLs, originating from the industrial wastes, were able to migrate through the local clayey-silty aquitards, allowing the development of different dissolved plumes, currently migrating in the three investigated aquifers (down to 60 m b.g.s.). Within the shallower portion of the system, the sediments contain a high amount of solid phase organic carbon (peaty layers) that promote an anoxic environment and reductive dechlorination of PCE and TCE to other chlorinated compounds, incl. Vinyl Chloride (VC), which occurs in very high concentrations. The occurrence of VC a few meters beneath the ground surface represents a potential threat for the local residents. Although Tier II site specific risk assessment suggests a high level of risk concerning vapor intrusion to indoor air and inhalation, no evidence of actual VC emissions at the surface were found at the site by a variety of Tier III monitoring approaches (i.e. flux-chamber, indoor gas monitoring, soil-gas survey). The case of the Caretti site highlights some of the criticalities related to the presence of PCE and TCE in groundwater beneath an urban area. These criticalities, together with the increased occurrence of urban sprawl all around Europe, suggest the need to consider PCE and TCE as priority pollutants to be monitored, in order to verify the quality of aquifer bodies.