title: Origin of VC-only plumes from naturally enhanced dechlorination in a peat-rich hydrogeologic setting.
abstract: The occurrence of vinyl chloride (VC) is often a main concern at sites contaminated with chlorinated solvents due to its high degree of toxicity and carcinogenicity. VC occurrence in aquifers is most often related to the degradation of higher chlorinated ethenes or ethanes and it is generally detected in plumes along with parent contaminants. However, specific combination of stratigraphic, hydrogeologic and geochemical conditions can enhance the degradation of parents and lead to the formation of plumes almost entirely composed of VC (i.e. VC-only plumes). This paper investigates the causes of VC-only plumes in the aquifers below the city of Ferrara (northern Italy) by combining multiple lines of evidence. The City of Ferrara is located on an alluvial lowland, built by the River Po, and is made up of alternating unconsolidated sandy aquifer and silt-clay aquitard deposits of fluvial origin. This region has been strongly impacted by prior industrial activities, with the occurrence of chlorinated compounds at several sites. VC-only plumes with uncertain source location were found at two contaminated sites. The source zone of a third plume composed of chloroethenes from PCE to VC was investigated for high resolution depositional facies architecture and contaminant distribution (contaminant concentration and Compound Specific Isotope Analysis - CSIA). The investigation suggested that degradation of PCE and TCE takes place during contaminant migration through peat-rich (swamp) layers related to the Holocene transgression, which locally act as a "reactor" for stimulating degradation with the accumulation of VC in the strongly reducing environment of the peat. Regional-scale stratigraphic architecture showed the ubiquitous occurrence of swamp layers at distinct stratigraphic levels in the investigated system and their apparent linkage to the in situ creation of the VC-only plumes.
authors.affiliation: Department of Biological, Geological and Environmental Sciences, Alma Mater Studiorum University of Bologna, via Zamboni 67, 40126 Bologna, Italy. Electronic address: maria.filippini3@unibo.it.
authors.forename: Maria
authors.initials: M
authors.lastname: Filippini
authors.affiliation: Department of Biological, Geological and Environmental Sciences, Alma Mater Studiorum University of Bologna, via Zamboni 67, 40126 Bologna, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Amorosi
authors.affiliation: Department of Biological, Geological and Environmental Sciences, Alma Mater Studiorum University of Bologna, via Zamboni 67, 40126 Bologna, Italy.
authors.forename: Bruno
authors.initials: B
authors.lastname: Campo
authors.affiliation: Helmholtz Center for Environmental Research - UFZ, Department for Isotope Biogeochemistry, Permoserstrasse 15, 04318 Leipzig, Germany.
authors.forename: Sara
authors.initials: S
authors.lastname: Herrero-Martìn
authors.affiliation: Helmholtz Center for Environmental Research - UFZ, Department for Isotope Biogeochemistry, Permoserstrasse 15, 04318 Leipzig, Germany.
authors.forename: Ivonne
authors.initials: I
authors.lastname: Nijenhuis
authors.affiliation: G(360) Centre for Applied Groundwater Research, School of Engineering, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Beth L
authors.initials: BL
authors.lastname: Parker
authors.affiliation: Department of Biological, Geological and Environmental Sciences, Alma Mater Studiorum University of Bologna, via Zamboni 67, 40126 Bologna, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Gargini
mesh_terms: D002947:Cities; D004784:Environmental Monitoring; D060587:Groundwater / Q000032:analysis* / Q000737:chemistry; D054879:Halogenation; D007558:Italy; D012987:Soil; D014752:Vinyl Chloride / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D012987:Soil; D014874:Water Pollutants, Chemical; D014752:Vinyl Chloride
keywords: Depositional facies; Ferrara; Plume; Reductive dechlorination; Swamp deposits; Vinyl chloride