A new multicomponent variably saturated flow and transport model

The migration of many naturally occurring elements and contaminants in soil and sediments is affected by a multitude of complex, interactive physical, chemical, mineralogical, and biological processes. Computer simulation of the interaction of these processes requires a coupled reactive transport code that integrates the physical processes of water flow and advective-dispersive solute transport with a range of biogeochemical processes. Such coupled codes are necessary tools for evaluating waste management and pollution control scenarios. The objective is to develop, test, and apply a new reactive transport code that is the result of coupling two existing codes: the water flow and solute transport code HYDRUS-1D and the geochemical code PHREEQC-2. This new code, called HP1, expands significantly the possible applications of the individual codes by integrating water flow, solute transport, heat transport and biogeochemical reactions. The advantage of such coupled codes is that for example, relationships between changing flow conditions (from saturated to unsaturated flow and vice versa) and chemical conditions (from reducing to oxidising, or from low to high pH and vice versa) are accounted for. This allows a more accurate description