Nonequilibrium sorption in soil/bentonite barriers

This installation of soil/bentonite (SB) slurry walls is a popular strategy for containing subsurface contamination. An important aspect of performance assessment for SB systems is an evaluation of the rate of contaminant transport across the barrier. The one-dimensional (1D) advective-dispersive-reactive equation is often applied to this analysis, under the common assumption of linear local equilibrium sorption. For cases in which sorption to barrier materials is not rapid, application of the local equilibrium assumption in the design and analysis of barrier systems will be nonconservative. Computational strategies are presented for incorporating first-order kinetic sorption into predictions of 1D contaminant transport in vertical walls. In particular, an extension to the popular finite-layer approach is developed that allows treatment of nonequilibrium sorption while retaining the computational advantage associated with the semianalytical framework. Application of the method is illustrated through sensitivity analysis and simulation of published experimental results. While it is unlikely that nonequilibrium sorption will influence the performance of installed slurry walls, it is suggested that kinetic effects may complicate the interpretation of laboratory experiments for some systems.

[1]  P. F. Hudak,et al.  Alternatives for Ground Water Cleanup , 1995 .

[2]  N. Thompson,et al.  Review and evaluation , 1996 .

[3]  P. V. Danckwerts.  Continuous flow systems. Distribution of residence times , 1995 .

[4]  C. Chrysikopoulos,et al.  Analytical Models for One‐Dimensional Virus Transport in Saturated Porous Media , 1995 .

[5]  A. Valocchi,et al.  Constraints on the Validity of Equilibrium and First-Order Kinetic Transport Models in Structured Soils , 1986 .

[6]  Cass T. Miller,et al.  Development of split‐operator, Petrov‐Galerkin Methods to simulate transport and diffusion problems , 1993 .

[7]  Mark L. Brusseau,et al.  The influence of sorbate-organic matter interactions on sorption nonequilibrium , 1989 .

[8]  Joseph J. Pignatello,et al.  Mechanisms of Slow Sorption of Organic Chemicals to Natural Particles , 1996 .

[9]  Jack C. Parker,et al.  Determining transport parameters from laboratory and field tracer experiments , 1984 .

[10]  L. Katz,et al.  Sorption phenomena in subsurface systems: Concepts, models and effects on contaminant fate and transport , 1991 .

[11]  P. R. Schroeder,et al.  Contaminant transport modeling , 1995 .

[12]  Cass T. Miller,et al.  Two‐dimensional modeling of aquifer remediation influenced by sorption nonequilibrium and hydraulic conductivity heterogeneity , 1994 .

[13]  P. V. Danckwerts.  Continuous flow systems , 1953 .

[14]  Albert J. Valocchi,et al.  Accuracy of operator splitting for advection‐dispersion‐reaction problems , 1992 .

[15]  J. Bear.  Dynamics of Fluids in Porous Media , 1975 .

[16]  Jeffrey C. Evans,et al.  Metals attenuation in minerally-enhanced slurry walls , 1997 .

[17]  Robert W. Gillham,et al.  Sorption nonideality during organic contaminant transport in porous media , 1989 .

[18]  Jagath J. Kaluarachchi,et al.  Critical assessment of the operator-splitting technique in solving the advection-dispersion-reaction equation: 1. First-order reaction , 1995 .

[19]  John R Booker,et al.  1‐D Pollutant Migration in Soils of Finite Depth , 1985 .

[20]  J. Bahr,et al.  Direct comparison of kinetic and local equilibrium formulations for solute transport affected by surface reactions , 1987 .

[21]  Robert M. Quigley,et al.  Clayey Barrier Systems for Waste Disposal Facilities , 1994 .

[22]  W. Weber,et al.  Sorption of Low Molecular Weight Organic Contaminants by Fly Ash: Considerations for the Enhancement of Cutoff Barrier Performance , 1992 .

[23]  A. Talbot.  The Accurate Numerical Inversion of Laplace Transforms , 1979 .