Impact on groundwater of concurrent leakage and diffusion of dichloromethane through geomembranes in landfill liners

摘要

ABSTRACT: Although intact geomembranes are excellent barriers to fluid flow, there are still twonpossible pathways for the transport of organic contaminants into the environment: leakage throughndefects in the geomembrane, and diffusion through the intact geomembrane. Analytical, semi-nanalytical and numerical techniques for calculating leakage rates have been developed. However, nonprevious attempt has been made to rigorously model the interaction between leakage through anhole in a wrinkle and diffusion. To address this shortcoming, finite-element analyses in two-ndimensional space are performed to simulate the transport of dichloromethane (DCM) through anleaking HPDE geomembrane (GM) for eight cases involving composite liners, including bothncompacted clay liners and geosynthetic clay liners. Equations of steady-state seepage and time-ndependent diffusion-advection in saturated soils are solved. Transport through the GMs is simulatednby a novel, mass-conserving equivalent boundary condition that renders the problemncomputationally more tractable. Results are compared with those obtained from widely used one-ndimensional methods, namely the Rowe equation for leakage through a wrinkle and thenPOLLUTEv7 program for mass transport. It is shown that predictions of leakage and transport bynthe one-dimensional method (POLLUTEv7) are within a maximum 30% of two-dimensional valuesnunder conditions of perfect mixing in the aquifer. When no horizontal mixing is present,nconcentrations of DCM are found to increase by up to 43% in two-dimensional analyses. It isnconcluded that one-dimensional analyses are adequate for most practical purposes.