GeoSysBRNS—A flexible multidimensional reactive transport model for simulating biogeochemical subsurface processes

The description of reactive transport processes in subsurface environments requires a sound understanding of both the biogeochemical complexity of the system and the spatially resolved transport of reactive species. However, most existing reactive transport models, for example in the field of contaminant hydrology, are specialized either in the simulation of the reactive or of the flow and transport processes. In this paper, we present and test the coupling of two highly flexible codes for the simulation of reactive transport processes in the subsurface: the Biogeochemical Reaction Network Simulator (BRNS), which contains a solver for kinetically and thermodynamically constrained biogeochemical reactions, and GeoSys/RockFlow, a multidimensional finite element subsurface flow and transport simulator. The new model, named GeoSysBRNS, maintains the full flexibility of the original models. The coupling is handled using an operator splitting scheme, which allows the reactive solver to be compiled into a problem specific library that is accessed by the transport simulator at runtime. The accuracy of the code coupling within GeoSysBRNS is demonstrated using two benchmark problems from the literature: a laboratory experiment on organic carbon degradation in a sand column via multiple microbial degradation pathways, and a dispersive mixing controlled bioreactive transport problem in aquifers, assuming three different reaction kinetics.