CHARACTERIZING THE UNSATURATED AND SATURATED HYDRAULIC PROPERTIES OF COAL COMBUSTION BY-PRODUCTS IN LANDFILLS OF NORTHWESTERN NEW MEXICO 1

Coal combustion byproducts (CCBs) disposed of in unlined landfills can affect the quality of adjacent water resources. In previous studies, CCBs have been found to leach toxic heavy metals such as arsenic, mercury, and lead into groundwater. CCBs include fly ash, bottom ash, and flue-gas desulfurization product (FGD gypsum). Within a landfill, CCBs may be present at different densities associated with depth, compacted primarily from the weight of above materials. This investigation focused on determination of the unsaturated and saturated hydraulic properties of fly ash and bottom ash as a function of density and thus a function of depth within a landfill. Ash samples from a power plant in northern New Mexico were collected for laboratory analysis. Compressibility curves were developed in order to determine what densities may be experienced at a range of pressures. Saturated hydraulic conductivity was determined using falling head tests for multiple densities of each material. Moisture characteristic curves were developed from hanging column tests, pressure plate tests, dew point potentiometer measurements, and relative humidity measurements. The moisture characteristic curves were also measured at a range of densities for each material. Results indicated that the fly ash saturated hydraulic conductivity varied as a function of density for the materials tested and the density could be reasonably predicted using an equation presented. Fly ash unsaturated properties also show trends with variations in density with the variability decreasing as density increases. Fly ash in a landfill can have estimated density, unsaturated and saturated hydraulic properties as a function of depth using the methods in this paper. Bottom ash showed similar trends in compressibility with less variability with respect to the fly ash. The unsaturated and saturated hydraulic properties show some trends, though with high amounts of variability. The density of bottom ash materials in a landfill may be reasonably estimated using methods proposed in this study while unsaturated and saturated hydraulic properties have greater uncertainty.