Bottom ash from one mass-burn incinerator and one refuse derived fuel incinerator was subjected to laboratory testing and evaluation of physical and chemical properties and behavior. Testing was performed on natural bottom ash and bottom ash amended with other fine grained natural aggregates such as clay and coal fly ash. Gradation analyses show that bottom ash is similar in grain size distribution to a well-graded gravelly sand. Bottom ash has lower compacted density and specific gravity than a typical well-graded coarse grained natural aggregate but has equivalent or higher strength properties. This indicates bottom ash could be used as a structural fill. While pre- and post-processing have been used to remove ferrous particles, a significant quantity of ferrous particles remain following processing. The permeability of the bottom ash is similar to well-graded coarse grained natural aggregates but can be reduced significantly with the blending of fine-grained natural aggregates. The addition of 10 percent by weight of clay will reduce the permeability sufficiently to meet the USEPA criteria for a landfill cap/liner. Based on limited TCLP testing the bottom ash is categorized as non-hazardous under USEPA guidelines. However, batch and column leaching tests produce leachate that is alkaline and demonstrates elevated levels of soluble metals and salts. The levels of some soluble metals and chlorides in the leachate exceed USEPA drinking water standards indicating that further amending would be necessary to be able to use bottom ash outside the landfill setting.