Moisture Flow through Municipal Solid Waste: Patterns and Characteristics

Chris Zeiss
Wade Major



Vertical moisture flow through compacted municipal waste layers is more complex than the one-dimensional, uniform Darcian drainage flow through a constant homogeneous medium as modeled in HELP. Channeling and flow along wetting curves produce irregular and more rapid breakthrough times and leakage rates. Tests of compacted municipal waste show distinct channeled flow in two to three streams in cylindrical cells. Furthermore, practical field capacity is substantially lower at 0.136 than the HELP default value of 0.292. Porosity, while similar to the default value of 0.52, varies with compaction ratio from 0.58 to 0.47. As a result, practical unsaturated hydraulic conductivities are 104 to 105 higher at 1.2 · 10-3 to 1.7 · 10-2 cm/s than the HELP default of 1.2 · 10-7 cm/s. As a result, waste default values should be revised in current models, while new leachate generation models need to account for channeled flow.

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