Previous field and laboratory studies indicated a strong correlation between alkalinity of western fly ash leachate and trace element concentrations. These observations have raised concerns that subsurface disposal of fly ash may pose a groundwater contamination problem. These concerns would be minimized if a natural neutralization capacity existed in the materials surrounding the fly ash disposal sites. The natural carbonate buffer system known to exist in this region offered the possibility of providing this neutralization capacity. The neutralization capacity of overburden core samples obtained at lignite mine disposal sites in west-central North Dakota was examined and found to be a function of the concentration of the standard base. This eliminated as a sole mechanism of neutralization of the expected role of the carbonate-bicarbonate buffering system. The function of concentration appears to be related to cation activity rather than hydroxide equivalence, suggesting that cation exchange is an additional source of neutralization capacity. Hydrogen ion release provides the necessary conuter-ion to any alkaline species. Total organic content in the overburden materials is adequate (6 to 23% by weight) to allow the role of organic to be a reasonable consideration along with cation exchange on inorganic materials such as clays. The contributions to the neutralization capacity from these two sources is currently being explored along with other possibilities. 2 references, 2 figures, 3 tables.