Modeling Coupled Hydrologic and Chemical Processes: Long-Term Uranium Transport following Phosphorus Fertilization

TLDR: In this paper, the HP1 component transport simulator was used to predict the transport of two major elements (Ca and P) and one trace element (U) applied annually for 200 yr to a fi eld soil in the form of an inorganic P fermentation lizer.

Abstract: Coupling physical and geochemical processes within one integrated numerical simulator provides a process-based tool for invesƟ gaƟ ng the mobility of contaminants as aff ected by changing hydrologic regimes and geochemical condiƟ ons. We review interacƟ ons between physical and biogeochemical processes in the vadose zone, and then present a case study demonstraƟ ng these complex interacƟ ons. A hypotheƟ cal applicaƟ on is presented of the HP1 mulƟ component transport simulator to predict the transport of two major elements (Ca and P) and one trace element (U) applied annually for 200 yr to a fi eld soil in the form of an inorganic P ferƟ lizer. InteracƟ ons of Ca, P, and U with the solid phase are described using caƟ on exchange and surface complexaƟ on reacƟ ons. SimulaƟ ons assuming steady-state or transient fl ow condiƟ ons were analyzed in terms of temporal variaƟ ons of the linear distribuƟ on coeffi cient, K d , which depends strongly on pH and the composiƟ on of the aqueous phase. If the composiƟ on of the aqueous phase is constant, adsorpƟ on of Ca and U increases with increasing pH. Due to the annual addiƟ on of Ca, P, and U, and compeƟ Ɵ on between P and U for sorpƟ on sites, the K d of these elements decreased with Ɵ me near the soil surface. Deeper in the soil, the K d of U followed the pH increase because of a lack of compeƟ Ɵ on from P. Because of the combined eff ects of changing hydrologic and geochemical condiƟ ons, the Ca and U distribuƟ on coeffi cients and solute fl uxes during the transient simulaƟ on exhibited large short-Ɵ me variaƟ ons of up to three orders of magnitude.