Explicit simulation of microbial transport with a dual-permeability, two-site kinetic deposition formulation using the integrated surface–subsurface hydrological model HydroGeoSphere
Friederike Currle, René Therrien, and Oliver S. Schilling
2025
À retenir
Pour éviter que des microbes contaminent l’eau potable, il est important de comprendre comment ils se déplacent entre les rivières et les nappes souterraines. Actuellement, la délimitation des aires de protection des puits se base surtout sur des tests avec colorants, mais ces méthodes ne tiennent pas compte du fait que les microbes voyagent souvent plus vite que les substances dissoutes. Des chercheurs ont donc créé un outil qui simule à la fois le transport des microbes et des solutés dans l’eau, en tenant compte de leur adsorption sur les surfaces, de leur désorption et de leur inactivation. Cette avancée permet de mieux définir les zones à protéger autour des puits et d’évaluer les risques de contamination des puits en filtration sur berge, même lors d’événements extrêmes comme les inondations.
Résumé
Assessing the transport behaviour of microbes in surface water–groundwater systems is important to prevent contamination of drinking-water resources by pathogens. While wellhead protection area (WHPA) delineation is predominantly based on dye injection tests and advective transport modelling, size exclusion of colloid-sized microbes from the smaller and usually less conductive pore spaces causes a faster breakthrough and thus faster apparent transport of microbes compared to that of solutes. Pour un public non scientificTo provide a tool for better assessment of the differences between solute and microbial transport in surface water–groundwater systems, here, we present the implementation of a dual-permeability, two-site kinetic deposition formulation for microbial transport in the integrated surface–subsurface hydrological model HydroGeoSphere (HGS). The implementation considers attachment, detachment, and inactivation of microbes in both permeability regions and allows for multispecies transport. The dual-permeability, two-site kinetic deposition implementation in HGS was verified against an analytical solution for dual-permeability colloid transport. The suitability of the model for microbial transport in integrated surface–subsurface hydrological settings at the wellfield or small headwater catchment scale is demonstrated by two illustrative examples. The first example is a benchmark for integrated rainfall–runoff and streamflow generation modelling to which we added microbial transport from a conceptual manure application, demonstrating the novelty of explicit and coupled microbial and solute transport simulations in an integrated surface–subsurface hydrological scenario. The second example is a multi-tracer flow and transport study of an idealized alluvial riverbank filtration site, in which we simulate in parallel the transport of reactive microbes, conservative 4He, and reactive 222Rn, demonstrating the assessment of mixing ratios, tracer breakthrough curves, and travel times in an integrated manner via multiple approaches. The developed simulation tool represents the first integrated surface–subsurface hydrological simulator for reactive solute and microbial transport and marks an important advancement to unlock and quantify governing microbial transport processes in coupled surface water–groundwater settings. It enables meaningful WHPA delineation and risk assessments of riverbank filtration sites with respect to microbial contamination even under situations of extreme hydrological and microbial stress, such as flood events.
mots clés:
Wellhead protection area delineation, Microbial transport, HydroGeoSphere, Dual-permeability, Riverbank filtration sites, Surface water–groundwater systems