Groundwater pollution by organic compounds: a three-dimensional boundary element solution of contaminant transport equations in stratified porous media with multiple non-equilibrium partitioning

Abstract

Industrial contaminants and landfill leachates, particularly those with high organic content, may migrate into groundwater streams under conditions of non-equilibrium partitioning. These conditions may either be induced by time-dependent sorption onto the soil skeleton and intra-sorbent diffusion in the soil matrix, or by heterogeneous advective fields within the pore. These processes are known as chemical and physical non-equilibrium processes respectively, and may result in significant deviations from the paths predicted by steady-state partitioning assumptions. In addition, multi-directional soil properties, soil stratification and complex geometries of the pollution source may require a full three-dimensional analysis for accurate contamination prediction. A three-dimensional boundary element solution of the time-dependent diffusive/advective equation in non-homogeneous soils with both physical and chemical non-equilibrium processes is developed. Saturated conditions and rate-limited mass transfer are assumed. The Laplace transform removes the need for time-stepping and the associated numerical complexity, and the use of Green's functions yields accurate solutions of infinite and semi-infinite domains such as soils as well as media with finite dimensions. The solution requires boundary discretization only and can therefore be a valuable tool in bio-remediation and landfill design where different geometries, soil properties and pollutant loads may be analysed at low cost. The proposed technique is validated by comparing its predictions to analytical solutions obtained for different types of soil and contaminant sources. The scope of the method is illustrated by analysing the contamination of multi-layered soils by a neighbouring river and a surface source. Copyright © 1999 John Wiley & Sons, Ltd.