Analytical solution of leachate flow to vertical wells in municipal solid waste landfills using a dual-porosity model

In this study, a flow model of leachate to vertical wells in municipal solid waste (MSW) landfills has been established using a dual-porosity model. The proposed model divides waste into fracture and matrix domains, the leachate in these two domains flows horizontally and vertically into a vertical well together, and mass exchange occurs between them. An analytical solution of leachate drawdown under vertical wells pumping at a constant rate is obtained through Laplace integral transformation and Separation of variables method. A sensitivity analysis indicates that the hydraulic characteristics of the fracture domain (i.e., kfr and μsf) have greater influence on leachate drawdown than that of the matrix domain (i.e., kmr and μsm). As the proportion of the fracture domain within the total domain, wf, increases, additional large pores are available for leachate flow, and leachate drawdown gradually decreased. As the anisotropy of hydraulic conductivity, kr/kz, increases, it becomes increasingly difficult for leachate to flow downward, and leachate drawdown gradually decreases. A case study of vertical well pumping tests at the Chang'an and Liming landfills indicated that the proposed model performed better than the Theis model in leachate drawdown estimation. The values of wf and kfr/kmr were set to be 0.45 and 500 for the MSW in the Chang'an and Liming landfills, respectively.