Gas migration model for sanitary landfill cover systems

Anaerobic degradation of solid waste within a sanitary landfill produces methane and carbon dioxide, collectively known as landfill gas (LFG). Methane, a greenhouse gas, has a global warming potential 21 times that of carbon dioxide. It is estimated that about 10% of global anthropogenic methane emissions are from landfills. Therefore there is a considerable interest to control methane emissions from landfills.; Determination of source strength and “hotspots” within a landfill are necessary to design LFG extraction systems. Currently, the source strengths and “hotspots” are determined using pumping tests. Due to high cost and uncertainties involved in conducting a pumping test, an alternative method is needed. A model incorporating a geostatistical technique and a 1-D numerical model to determine source strength of LFG and to locate “hotspots” at the waste-cover interface was developed.; A 1-D advective-dispersive-reactive gas migration model with constant concentration boundary conditions was developed and used to estimate the LFG source strength and emission. The model was calibrated and tested in the laboratory and in the field. The results indicated that 1-D numerical model is a suitable technique to estimate LFG source strength, cover soil oxidation and emission.; Kriging, an unbiased geostatistical technique with known minimum variance, was used to interpolate spatially varied data related to porous media gas migration. Both 1-D numerical model and kriging were integrated within a GIS frame work to formulate a pseudo 3-D model. The GIS was used to store and analyze spatially varied data, organize the input data to the numerical model and, to graphically represent the results. GIS techniques were automated using Arc Macro Language (AML) programs with menu driven operations. Laboratory and pilot scale field experiments were conducted to obtain data to calibrate and test the pseudo 3-D model. Results indicated that kriging can be used to interpolate cover surface elevation, waste surface elevation and gas concentrations at waste-cover interface. The model outputs included spatially varied source strengths and emissions as well as total source strength and total emission of LFG. “Hotspots” were identified from the contour maps of source strength.