Liquid Head on Landfill Liners Due to Leachate Recirculation

Abstract

Due to the financial and environmental incentives offered by leachate recirculation, leachate recirculation is a widely used leachate management option for municipal solid waste (MSW) landfills. However, more commonly, leachate collection systems (LCSs) of landfills are designed primarily for leachate impingement from infiltration of precipitation. Hence, when leachate is recirculated in landfills, many LCSs do not have the hydraulic capacity to drain the recirculated leachate and maintain the leachate head on the liner below the federal regulatory requirement equal to 0.3 m. Leachate head build up data for injected liquids in MSW landfills is virtually non-existent. In this study, we have numerically simulated leachate injection using two most commonly used methods: (1) horizontal trenches; and (2) vertical wells. We used the saturated/unsaturated flow model HYDRUS-2D. The simulations were conducted for a range of hydraulic conductivities of waste and the LCS drainage material and liquid injection rates. We have presented the results in such a way that designers can select appropriate design parameters to minimize excess liquid heads on liners. The simulated results indicate that pea gravel or materials having hydraulic conductivity greater than 1 cm/s offer a better choice for LCS drainage material. Use of material having hydraulic conductivity less than 0.01 cm/s (e.g., sand) resulted in liquid head greater than 0.3 m for typical leachate injection rates used in landfills.