Field-Scale Evaluation of Lysimeters Versus Actual Earthen Covers

Abstract

Abstract This paper presents the design, construction, and monitoring of two uncompacted and one compacted clay field-scale test sections that were built and instrumented at a landfill near Detroit (Michigan). This was accomplished to capture the differences in the hydraulic and hydrologic responses of actual caps overlying the municipal solid waste (MSW) versus the corresponding lysimeters. While the lysimeter pans were installed in the middle of each of the three test sections to measure percolation, the instrumented area of the test section was expanded upslope and downslope of the lysimeter to monitor the soil water storages within and beyond the lysimeter footprint. About 35 sensors were installed in each of the three test sections to monitor water contents, water potentials, soil temperatures, water levels, and gas pressures. The soil water storages for the uncompacted test sections that were underlain by the waste were typically greater than those for the corresponding lysimeters. However, for the compacted test section, there was no significant difference between the soil water storage for the actual cap and the lysimeter. The percolation rate for the compacted clay test section was on the order of a few millimeters per year, while that for the uncompacted test sections were in the order of tens of centimeters per year. This difference is attributed to the two order of magnitude lower hydraulic conductivity of the compacted clay. The field data collected in this project validates previously published numerical results regarding hydraulic differences between lysimeters and actual caps.