RESPONSE project: Reactive transport of point source contamination in soils and groundwater

The RESPONSE project aims at improving the use of coupled reactive transport models to simulate the fate of
inorganic and organic contaminants within environments, characterised by a fluctuating shallow groundwater
table – inducing strong hydraulic, physico-chemical and redox gradients. Three case studies were selected based
on the presence of inorganic and/or organic contamination. Two sites are cemeteries where groundwater pollution
by herbicides (2,6-dichlorobenzamide (BAM) – a persistent metabolite of herbicide dichlobenil) was detected. Top
soil and groundwater samples were collected and the BAM degradation and mineralization potential of soil
microbiota is tested in the laboratory. It is hypothesized that BAM degradation is strongly affected by DOC quality
(measured through specific UV absorbance) and quantity. RESPONSE will investigate whether predictions of
dichlobenil and BAM migration in soils and groundwater can be improved by taking into account DOC
quality/quantity.The third site is a former municipal landfill, where redox zonation and contamination by As is
observed. This site is primarily used to study the level of hydrogeological and geochemical detail needed to
predict the migration of pollutants in a satisfactory way. This hypothesis is tested by comparing predictions using
site specific measured parameters (soil and subsoil hydraulic parameters, in-situ groundwater flow
characterization, etc.) with predictions using parameters inferred from existing hydrological/ geochemical data
available in data bases. Moreover, an integrated tool is developed to simulate water flow and reactive solute
transport in the subsurface focusing on the water table interface. This is achieved by loosely coupling the existing
HYDRUS, MODFLOW, MT3D-USGS and PHREEQC codes at the lowest level and adding functionalities for the
transfer of solute concentrations. The HYDRUS package for MODFLOW (Seo et al., 2007) has been updated and
PHREEQC functionalities are coupled to both the unsaturated zone (based on HPx software; Jacques et al., 2018)
and the saturated zone.