Analytical modeling of aquifer decontamination by pumping when transport is affected by rate‐limited sorption

Abstract

Aquifer cleanup efforts at contaminated sites frequently involve operation of a system of extraction wells. It has been found that contaminant load discharged by extraction wells typically declines with time, asymptotically approaching a residual level. Such behavior could be due to rate‐limited desorption of an organic contaminant from aquifer solids. An analytical model is presented which accounts for rate‐limited desorption of an organic solute during cleanup of a contaminated site. Model equations are presented which describe transport of a sorbing contaminant in a converging radial flow field, with sorption described by (1) equilibrium, (2) first‐order rate, and (3) Fickian diffusion expressions. The model equations are solved in the Laplace domain and numerically inverted to simulate contaminant concentrations at an extraction well. A Laplace domain solution for the total contaminant mass remaining in the aquifer is also derived. It is shown that rate‐limited sorption can have a significant impact upon aquifer remediation. Approximate equivalence among the various rate‐limited models is also demonstrated.