Design Considerations for Lysimeters Used to Evaluate Alternative Earthen Final Covers

Alternative earthen final covers are being considered throughout North America as cost-effective alternatives to prescriptive covers. Regulatory agencies typically require field testing to demonstrate the equivalency of percolation rates from prescriptive and alternative covers. Lysimetry, which consists of collecting percolating water from the base of a test section, provides a direct measurement of the percolation rate, and can be used in equivalency demonstrations. This paper describes a modeling study that investigated how lysimeter geometry and boundary conditions affect lateral diversion and percolation rates measured using lysimeters. Lysimeters with various geometries were simulated with HYDRUS-2D using constant meteorological and vegetation data. Simulations showed that sidewalls, which are 0.35 m high, can minimize the lateral diversion of flow around the sides of the lysimeter. Up-slope and down-slope endwalls of lysimeters need to extend to the surface of the lysimeter, especially when the lysimeter is inclined (4:1 or 3:1 slope). Modeling has shown that lysimeters underestimate percolation by 8 to 14%. Based on these simulations and the writersʹ experience in the design and construction of lysimeters, a recommended design of lysimeters is suggested.