Assessing groundwater surface water interaction and groundwater discharge in a contaminated site in an industrial, sub-urbanized area

A contaminated site related to a former coke factory, located in the alluvial plain of the Meuse River near Liège was investigated to characterize the nature and extend of underground contamination. The major objective of the investigation was to evaluate whether an interaction exists, at the level of this particular site, between groundwater and surface water, despite the existence of river embankment, to assess the dynamics of such interactions and finally to quantify groundwater fluxes as the main potential vector of mobility of contaminants offsite. Field investigations consisted in (1) a very detailed monitoring of the dynamics of water levels in the Meuse River and in various piezometers located in the site; (2) the application of single well tracer tests using the Finite Volume Point Dilution Method (FVPDM) in different piezometers in order to obtain point estimates of Darcy fluxes. Using cross-correlation analysis, the strong relation between variations in the Meuse water levels and groundwater levels was clearly established. The FVPDM allowed obtaining point estimates of Darcy fluxes at various points along the Meuse-aquifer interface. Using an analytical solution for groundwater flow interaction with adjacent river allowed modelling accurately the dynamics of groundwater levels in function of the dynamics of the river water levels. All these results are presented, analyzed and integrated in order to quantify the groundwater discharge in the Meuse River