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GL1943-
2004, Liu, Xiaoli, PhD thesis, Florida State University, department of Civil and Environmental Engineering

Abstract:

Landfills are the most widely used facilities for solid waste disposal. Landfill covers are used to reduce the quantity of water that infiltrates into solid waste landfills, isolate solid waste from the environment and control gas migration. Resource Conservation and Recovery Act (RCRA) regulations prescribe that the covers employ layers which have low saturated hydraulic conductivity as hydraulic barriers. Those barriers can limit flow into underlying solid wastes, and consequently, reduce the rate of leachate generation and risk of additional groundwater contamination. Experience has shown that the prescribed clay barrier layers are susceptible to failure caused by desiccation and cracking damage by freeze ? thaw actions, and are expensive to build. An effective alternative cover design is Evapor-Transpiration (ET) cover. ET covers possess many advantages over prescribed covers such as working with nature, long life time, easy maintenance and lower cost. Once the feasibility of an ET cover is verified in a region, an evaluation of hydraulic equivalency is required for alternative cover to be approved by regulatory authorities. The hydraulic equivalency requires that percolation from the base of the alternative cover is less than or equal to percolation rate from the prescriptive cover. Lysimeters was suggested to be used in facilities measuring the percolation rate. There are some concerns about the precision with which percolation rate can be measured with lysimeters. A series of numerical simulations were performed in this study to investigate the performance of lysimeters of various geometries and develop the optimal lysimeters dimensions for percolation rate measurement. The simulations consist of inputting data for lysimeter geometry, soil hydraulic property, weather condition, boundary condition, vegetation distribution and density. The output cumulative flux data was used to evaluate the performance of lysimeters. The study shows at the specific weather condition, the lysimeters without sidewalls underestimate percolation rate by at least 25%. Installation of full sidewalls remarkably improved the lysimeter performance. The lysimeter with full scale sidewalls still underestimate by at least 10%. Lateral diversion and no-flow boundary at the bottom of lysimeter and the drainage layer right above the bottom pan caused the decrement of lysimeter performance. To measure percolation rate accurately, soil - specific and site - specific coefficients have to be determined. The coefficients can to be used to correct lysimeter performance.

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