Dynamics of chlorinated aliphatic hydrocarbons in the Chalk aquifer of northern France

• Published in: The Science of the total environment 2021-02, Vol.757, p.143742-143742, Article 143742
• Main Authors: Walaszek, Milena, Cary, Lise, Billon, Gabriel, Blessing, Michaela, Bouvet-Swialkowski, Aurélie, George, Melinda, Criquet, Justine, Mossmann, Jean Remi
• Format: Article
• Language: English
• Subjects: Compound-specific carbon isotope analysis; Depth-discrete sampling; Earth Sciences; Geochemistry; Groundwater; Passive sampler; Reductive dechlorination; Sciences of the Universe
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.143742

The Chalk aquifer used for drinking-water production in the southwest of the Lille European Metropolis is threatened by the presence of chlorinated aliphatic hydrocarbons (CHCs), their concentrations in groundwater regularly exceeding the regulatory limits for drinking water in France. This hinders its use for drinking-water production. Understanding the dynamics and spatial distribution of CHC in the aquifer is a key factor for resource sustainability. For that purpose, an intensive monitoring was undertaken in several well fields and at different depths over eight years. To assess a possible migration and/or degradation of the compounds, the water column in several wells was sampled at various depths with passive samplers. Furthermore, CHC degradation mechanisms were investigated with compound-specific carbon-isotope analysis. The CHC concentrations and their distributions in the area depend on past and current industrial activity, causing plumes emphasized by pumping in the wells, such plumes being multi-source with no identified origin in most wells. In the south area of Les Ansereuilles, reductive dechlorination of tetrachloroethylene from a former industrial laundry highly impacted the surrounding area with its main degradation product cis-1,2-dichloroethylene. The same area is also affected by tetrachlroroethylene from several industrial laundries, textile factories and dyeing industries with also an anaerobic degradation. In the northern part of Les Ansereuilles, tetrachloroethylene, trichloroethane, trichloroethylene and 1,1-dichloroethylene were found as primary products, whereas cis-1,2-dichloroethylene appears to be an anaerobic degradation product of TCE. The other well fields (Houplin-Ancoisne, Seclin and Emmerin) are less impacted by CHC pollution, and it was shown that no CHC degradation occurred in the wells. However, the stratification of CHCs in the well-water columns, their constant concentration values over time caused by the large amount of available CHCs, and the minor degradation occurring in wells are of concern for water operators in the future. [Display omitted] •Chlorinated hydrocarbons in groundwater limit its use for drinking-water production.•Eight-years of CHC monitoring and compound-specific carbon-isotope analyses in 22 wells•Evidence of reductive dechlorination or absence of degradation is found.•Redox conditions and degree of reductive dechlorination vary on a small scale.