Effects of Compression and Decomposition on Saturated Hydraulic Conductivity of Municipal Solid Waste in Bioreactor Landfills

Laboratory and field-scale tests were conducted to determine the saturated hydraulic conductivity (Ks) of fresh and degraded municipal solid waste (MSW) at multiple dry unit weights and void ratios (e). Field-scale Ks was obtained from numerical inversion of data from the Deer Track Bioreactor Experiment (DTBE). Reasonable prediction of field-Ks can be achieved from large-scale laboratory tests if laboratory specimens are prepared from MSW with composition and dry unit weight similar to field conditions. In both the laboratory and field, Ks of MSW decreased with increasing dry unit weight as the voids become smaller. At constant dry unit weight, more decomposed MSW had higher void ratio and Ks. The relationship between Ks and void ratio of MSW was consistent for a range of decomposition states, suggesting that void ratio is a better indicator of Ks than dry unit weight. An empirical relationship between Ks and void ratio was developed that predicted the measured Ks of MSW in this study within one order of magnitude. At field scale, however, the effects of decomposition on Ks of MSW are more complex because decomposition and settlement occur simultaneously and have opposite effects on void ratio, complicating prediction of Ks.