title: Assessing the effect of grain-scale sorption rate limitations on the fate of hydrophobic organic groundwater pollutants.
abstract: Subsurface pollutant transport models accounting for sorption rate limitations are computationally more demanding than those assuming local sorption equilibrium. We combine batch and column tests with modeling for a comparative assessment of different sorption models. For the relatively hydrophobic compound naphthalene, a model assuming local sorption equilibrium was unable to reproduce breakthrough curves in column studies with Canadian River Alluvium sediment which contains carbonaceous particles. Fully calibrated independent forward predictions of a first-order kinetic and two diffusion kinetic sorption models were in much better agreement with the experimental data. Predictions using a diffusion-limited kinetic sorption model assuming concentration-independent sorption coefficients performed equally well as a model using the Freundlich isotherm. Both diffusion-based kinetic sorption models were superior to the first-order rate approach. In the present study, the validity of the local sorption equilibrium assumption is discussed based on a Damköhler number and thus, the compound's sorption properties, the aquifer properties, and the scale of the process. Relatively high groundwater velocities in combination with a low sorption coefficient K(d) and slow diffusion limited sorption kinetic rates are necessary conditions to justify the implementation of grain-scale sorption rate limitations in groundwater contaminant fate models. Such conditions exist when a low amount of carbonaceous particles is present in aquifers with high permeability.
authors: School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, England, United Kingdom.
authors: David
authors: D
authors: Werner
authors: Hrissi K
authors: HK
authors: Karapanagioti
authors: David A
authors: DA
authors: Sabatini
mesh_terms: D000327:Adsorption; D001554:Benzene / Q000032:analysis / Q000737:chemistry; D001555:Benzene Derivatives / Q000032:analysis / Q000737:chemistry; D004058:Diffusion; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry*; D060587:Groundwater / Q000032:analysis*; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008956:Models, Chemical; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*
chemical_list: D001555:Benzene Derivatives; D014874:Water Pollutants, Chemical; D001554:Benzene