Abstract
An abandoned industrial site in Belgium, located in the catchment of a chalk aquifer mainly used for drinking water, has been investigated for groundwater pollution due to a mixture of chlorinated solvents with mainly 1,1,1-trichloroethane (1,1,1-TCA) at high concentrations. The observed elevated groundwater mineralization was partly explained by chemical reactions associated with hydrolysis and dehydrohalogenation (HY/DH) of 1,1,1-TCA in the chalky aquifer. Leaching of soluble compounds from a backfilled layer located in the site could also have influenced the groundwater composition. In this context, the objective of this study was to investigate the hydrochemical processes controlling groundwater mineralization through a characterization of the backfill and groundwater chemical composition. This is essential in the context of required site remediation to define appropriate remediation measures to soil and groundwater. Groundwater samples were collected for chemical analyses of chlorinated aliphatic hydrocarbons, major ions, and several minor ones. X-Ray Diffraction Analysis (XRD), Scanning Electron Microscopy (SEM) and a leaching test according to CEN/TS 14405 norm were carried out on the backfill soil. δ34S and δ18O of sulphate in groundwater and in the backfill eluates were also compared. Both effects influencing the groundwater hydrochemistry around the site were clarified. First, calcite dissolution under the 1,1,1-TCA degradation reactions results in a water mineralization increase. It was assessed by geochemical batch simulations based on observed data. Second, sulphate and calcium released from the backfill have reached the groundwater. The leaching test provided an estimation of the minimal released quantities.
Highlights
Chlorinated aliphatic hydrocarbons (CAHs) are among the most common pollutants in industrial sites because of their intensive use as cleaning and degreasing products [1]
Using 1,1,1-TCA concentrations with observed field temperatures, these simplified simulations provide an estimation of Ca2+ and HCO3 − releases in the presence of hydrolysis and dehydrohalogenation (HY/DH) of 1,1,1-TCA in the chalk aquifer
Using a combination of tests on the backfill material extracted from the site and groundwater quality analyses, the mechanisms that lead to changes in groundwater mineralization
Summary
Chlorinated aliphatic hydrocarbons (CAHs) are among the most common pollutants in industrial sites because of their intensive use as cleaning and degreasing products [1]. Abiotic degradation of 1,1,1-TCA by hydrolysis and dehydrohalogenation (HY/DH) occurs independently of redox conditions in groundwater [13], it influences the pH that would impact the groundwater mineralization In this case, a hydrogeochemical investigation including major ions analysis allow a direct link between degradation reactions and mineralization changes, as long as no additional pollution source influencing groundwater mineralization can be identified. The presence of a backfill layer at the site has allowed to presume the leaching of different chemical compounds with water infiltration that may affect groundwater composition In this context, the general objective of the investigation is to better characterize and to quantify the hydrochemical processes controlling groundwater mineralization, through a combined approach of groundwater chemistry investigation with backfill soil characterization. The used method is based on groundwater analyses, laboratory backfill soil characterization and the study of sulphate isotopic signature in groundwater, along with the one in backfill eluates
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