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The long-term disposal of ash from brown coal combustion requires a thorough understanding of the geochemical controls on leachate quality. The geochemistry of leachate in ash generated from the combustion of coal in the Latrobe Valley region of Victoria, Australia, has been studied in the field and laboratory. The field studies, conducted over 14 months, showed active leaching and changes in leachate chemistry in the ash with mobilization of some trace elements. A further series of laboratory columns demonstrated similar leaching dynamics. Geochemical modeling indicated that both sulfate and carbonate minerals are the most likely solubility-controlling mineral phases in the ash. For regularly detected trace elements, such as As, Ba, and B but particularly Mo, Se, and Sr, the trends suggest that adsorption and coprecipitation controls are also important. The overall approach adopted in this paper has enabled a more realistic assessment of the controlling processes for solute transport during the active leaching phase of ash disposal, thereby improving long-term environmental management. DOI: 10.1061/(ASCE)0733-9372(2004)130:12(1514) CE Database subject headings; Fly ash; Environmental impacts; Leaching; Waste disposal; Australia; Coal.