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

Industrial contaminants and landfill leachates, particularly those with hig h organic content, may migrate into groundwater streams under conditions of non-equilibrium partitioning. These conditions may either be induced by ti me-dependent sorption onto the soil skeleton and intra-sorbent diffusion in the soil matrix, or by heterogeneous advective fields within the pore. The se processes are known as chemical and physical non-equilibrium processes r espectively, and may result in significant deviations from the paths predic ted by steady-state partitioning assumptions. In addition, multi-directiona l soil properties, soil stratification and complex geometries of the pollut ion source may require a full three-dimensional analysis for accurate conta mination prediction. A three-dimensional boundary element solution of the time-dependent diffusi ve/advective equation in non-homogeneous soils with both physical and chemi cal non-equilibrium processes is developed. Saturated conditions and rate-l imited mass transfer are assumed. The Laplace transform removes the need fo r time-stepping and the associated numerical complexity, and the use of Gre en's functions yields accurate solutions of infinite and semi-infinite doma ins such as soils as well as media with finite dimensions. The solution req uires boundary discretization only and can therefore be a valuable tool in bio-remediation and landfill design where different geometries, soil proper ties and pollutant loads may be analysed at low cost. The proposed techniqu e is validated by comparing its predictions to analytical solutions obtaine d for different types of soil and contaminant sources. The scope of the met hod is illustrated by analysing the contamination of multi-layered soils by a neighbouring river-and a surface source. Copyright (C) 1999 John Wiley & Sons, Ltd.