Analytical analysis of the leachate flow to a horizontal well in dual-porosity media

Abstract

Horizontal wells are gradually used for dewatering at municipal solid waste (MSW) landfills in recent years. A theoretical model of leachate flow to horizontal well is required to better evaluate its dewatering performance. In this study, a dual-porosity model of the leachate flow to a horizontal well in MSW landfills is established. The proposed model divides waste into fracture and matrix domains. Leachate in these two domains flows horizontally and vertically into a horizontal well together with leachate exchange occurring between them. An analytical solution of leachate level drawdown under horizontal well draining is obtained through Laplace integral transformation and Separation of variables. The analytical solution is verified with the numerical solution obtained by finite element method in COMSOL Multiphysics software. A sensitivity analysis is performed to investigate the effect of model key parameters, including anisotropy of hydraulic conductivity kr/kz, hydraulic conductivity ratio of fracture domain to matrix domain kfr/kmr, and proportion of fracture domain in total domain wf, on leachate level drawdown. A case study of the horizontal well draining test at the Tianziling landfill indicated that the dual-porosity model performed better than the single-porosity model in leachate level drawdown estimation, especially near the horizontal well. The average value of hydraulic conductivity ratio of fracture domain to matrix domain kfr/kmr is fitted to be 419 for typical MSW with high kitchen waste content in China.