A. INTRODUCTION This is the final technical report of the above-mentioned EMSP project. It summarizes the activities under that project throughout its lifetime. The project formally covers the period of September 15, 1998 to September 14, 2004, which includes the original project (from 1998), a three-year extension (starting September 15, 2000) and a no-cost extension of one year. In fact, even this six-year period follows at the heels of earlier EMSP and other projects by the same PI's from PNNL and Notre Dame (and from Argonne prior to that), which resulted in a broad outline of the chemistry in the Hanford waste tanks. Of particular emphasize in these projects was the generation and retention of flammable gas mixtures in the tanks and the interaction of organics compounds in the tanks with the ionizing radiation of the mixedwaste. Annual technical reports were regularly and on time submitted, and therefore, this report should be consulted with the previous reports, as well as the many publications that resulted from the activities associated with this project. The list of PI's given above includes various participants that contributed substantively at various degrees to understanding of the relevant chemistry of the system over the years. This project addressed generic safety concerns that arise at essentially all high-level waste (HLW) storage sites. It focused on the effects of organic chemicals in stored nuclear waste and their impact on pretreatment and tank closure issues. Managing the tank wastes and site cleanup activities requires understanding of the chemistry of organics in aqueous basic solutions that contain high nitrate and nitrite concentrations under the field of γ and β irradiation. We quantitatively characterize the important chemical processes that are induced by radiolysis of the organic complexants, and their degradation products, during the storage in tanks. Furthermore, concerns that arise from pretreatment and tank