An Evidence-Based Experimental Methodology for Directional Hydraulic Conductivity Measurement of Aged Municipal Solid Waste

Abstract

Municipal solid waste (MSW) is highly heterogeneous, and its hydraulic behavior can vary with flow direction, influencing leachate migration and subsurface hydrology in landfill systems. This study examined directional hydraulic conductivity (K) in MSW and assessed how waste characteristics affect laboratory test selection. Twelve samples were collected from a dumping yard at a depth of 6–9 m, representing waste aged approximately 2–6 years. A dual-direction laboratory setup was used to measure horizontal (Kh) and vertical (Kv) hydraulic conductivity under saturated conditions during a 37-day saturation period. For low-density MSW (<900 kg/m³) with a high proportion of flat 2D particles, the constant-head method was selected as the operationally appropriate steady-state method for the tested waste condition in the medium-flow range. Specific gravity (Gs) increased from 1.17 to 1.24 during saturation. The Kh reached 1.779 × 10⁻⁷ m/s and remained consistently higher than Kv, with an average anisotropy ratio (Kh/Kv) of 1.78. The observed anisotropy shows that waste fabric and depositional arrangement strongly control flow direction. Although based on degraded MSW from a single dumping yard, the findings provide practical guidance for selecting laboratory K testing methods for heterogeneous waste and subsurface hydrology protection in landfills.