This is an award to support research on the environmental reduction of chromium from the hexavalent to the trivalent state by contact with mineral and humic substances in soil, a reduction process that can be influenced by interactions with aqueous ions, electron transfers at mineral surfaces, reaction with simple organic molecules or by interactions with soil humic substances. This research involves determination of the oxidation-reduction processes that affect the transport and fate of hexavalent chromium in soil as influenced by ionic strength and background electrolytes. Results are expected to be used in the development of mathematical models that characterize the process by which chromium is chemically reduced and physically transformed to a less environmentally damaging form. Chromium is an important industrial metal that finds its way into surface and groundwaters by leakage from waste management sites. The results of this project are expected to be used in development of models and techniques that can be used in planning the engineering design of remediation measures that can be used to reduce the pollutional impact of chromium discharges on surface and groundwater.