Application of a continuous‐flow centrifugation method for solute transport in disturbed, unsaturated sediments and illustration of mobile‐immobile water

A centrifuge method was adapted for evaluating solute transport during steady state flow. Solute breakthrough curves were obtained on three sediment types at average water contents ranging from 14 to 84% moisture saturation. Interruptions in flow for sampling, a potential limitation of the method, had no apparent effect on breakthrough curves for the tracers and conditions evaluated. Compaction was observed for a silt loam sediment but was not observed for fine and coarse sand sediments. Regions of immobile water developed with decreasing moisture saturation; these results extend the range of previous reports. The continuum from a single to a multiregion flow domain was illustrated, and a modeling approach for estimating dispersion and mobile‐immobile water parameters was applied. The fraction of immobile water ranged from 48 to 80%; solute velocity in the mobile domain was up to fivefold greater than the average pore water velocity.