Analytical Model for Degradable Organic Contaminant Transport through a GMB/GCL/AL System

Abstract

An analytical model for degradable organic contaminant transport in a triple liner consisting of a geomembrane (GMB), a geosynthetic clay liner (GCL), and an attenuation layer (AL) was developed. Both advective transport through the defects of the GMB and diffusive transport in intact GMB are considered. The dimensionless analytical solution for semi-infinite bottom boundary condition was obtained by using the Laplace transformation. The method of separation of variables was used for the case with the fixed concentration bottom boundary condition. For the semi-infinite bottom boundary condition, with Damkohler number Q=1, the dimensionless concentration CN and the dimensionless flux FN increase by factors of 3.4 and 4.4, respectively, as the Peclet number of AL P1 increases from to 1. It is indicated that advection through the defects of the GMB is more important than diffusion in the intact part of the GMB in the cases with P1≥.26 when Q=1. Biodegradation plays a major role in organic contaminant transport in the triple liner with P1≤1 and Q≥1. As the length of the wrinkle Lw decreases from 1, to 1 m, the base flux decreases by factors of 49.6 and 11.1 for semi-infinite and fixed concentration bottom boundary conditions, respectively. The base flux decreases by a factor of 8.6 for the fixed concentration bottom boundary condition as the half-life of toluene decreases from 1 to 1 year. The hydraulic conductivity of GCL and the leachate head have a more important effect on the performance of the triple liner than the interface transmissivity and the permeability of AL based on the statistical analysis. The 2-year base flux for the scenario with length of wrinkle=1 m is the lowest. It is approximately 2.3 times less than the scenario with hydraulic conductivity of GCL=5×1−12 m/s for the case with fixed concentration bottom boundary, indicating the length of wrinkle has a more important influence on performance of the triple liner than the other involved parameters. The proposed analytical models can be used for evaluating experimental data, verifying complicated numerical models, and preliminary design of triple liners.