A knowledge of extra-trench processes related to oxidation-induced geochemical changes that are likely to occur when iron-rich, anoxic trench waters encounter an oxidizing environment along a redox gradient is essential for modeling radionuclide transport at low-level waste (LLW) disposal sites. The results of laboratory oxidation experiments on several trench leachates from the Maxey Flats site show that, upon oxidation, a series of geochemical changes were initiated that resulted in a drastically different solute geochemistry, involving oxidation of ferrous iron and subsequent precipitation of ferric oxyhydroxide, changes in alkalinity and acidity, a drastic increase in redox potential (Eh), and generally relatively little change in the concentrations of 60Co, 137Cs, and 85Sr in solution. The observations made in this study have important geochemical implications for the modeling of LLW sites in that the source term as an input parameter cannot be assumed to be constant, both spatially and temporally. The acid-generating potential and buffering capacity of an anoxic source term are important geochemical controls that maintain a balance between acidity and alkalinity and largely determine the nature and extent of oxidation-induced geochemical changes likely to occur along a redox gradient. The presence of organic chelating agents can alter the source term geochemistry to such an extent that authigenic ferric oxyhydroxide, which represents a geochemical discontinuity at the redox interface along leachate migration paths, proves to be a relatively ineffective sink for radionuclides.