Developing a Design Approach to Reduce Methane Emissions from California Landfills

This paper describes a modeling activities consisting of several tasks. One task involved the development and/or the use a multiphase flow model designed to simulate water, heat, and gas flow through landfill covers. The numerical model was developed by a research team at Florida State University that combines water and heat flow with a gas transport and oxidation model. The volumetric water content and temperature profiles of landfill cover were predicted using a water and heat flow model in variably saturated soils. Volumetric water content and temperature were generated at each node each day by knowing the unsaturated soil properties and average daily climatic data. The model was used to determine the methane oxidation capacity of several cover designs under any climatic conditions. In order to get the most immediate impact, this methodology was initially developed for use in California and will eventually be extended to the entire country. The soil physics-based model provide landfill owners, engineers, and the solid waste industry with a tool to: (1) evaluate cover designs in-terms of their capacity to oxidize methane under different climatic conditions, (2) estimate the time at which a gas collection system can be turned off, and (3) an additional model that can be incorporated within AP-42 to better predict and inventory landfill gas emissions.