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

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 C-N and the dimensionless flux F-N increase by factors of 3.4 and 4.4, respectively, as the Peclet number of AL P-1 increases from 0 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 P-1 >= 0.26 when Q = 1. Biodegradation plays a major role in organic contaminant transport in the triple liner with P-1 <= 1 and Q >= 1. As the length of the wrinkle L-w decreases from 1,000 to 100 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 100 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 20-year base flux for the scenario with length of wrinkle = 100 m is the lowest. It is approximately 2.3 times less than the scenario with hydraulic conductivity of GCL = 5 x 10(-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. (c) 2018 American Society of Civil Engineers.