Impact of grain scale heterogeneity on slow sorption kinetics

Groundwater contamination by dissolved organic compounds frequently occurs in valley aquifers that consist of highly heterogeneous sand and gravel sed iments. Remediation and risk assessment (e.g. reactive transport modeling) requires detailed information on the sorption/desorption kinetics in such a quifer materials. In this paper we present data on slow sorption kinetics o f phenanthrene and the composition of several aquifer materials that are ty pical for southern Germany and Switzerland. The heterogeneity of the aquife r material is described in terms of the physical and chemical properties (e .g., grain size, organic carbon content, intraparticle porosity, sorption p arameters, and rate constants for intraparticle diffusion) of the sediment constituents (lithocomponents). Phenanthrene sorptive uptake in a heterogen eous bulk sample can be predicted using a numerical model only if the compo sition and geochemical heterogeneity (different sorptivities and porosities of the lithocomponents) are considered. It could be shown that even within a narrow grain size fraction, the geochemical heterogeneity has to be inco rporated for the prediction of long-term sorptive uptake or release of orga nic contaminants.