Uranium mill tailings represent a potential threat to the human habitat by containing large amounts of radioactive and chemically toxic substances in high concentrations. The main objective of this investigation was to evaluate the actual movement and model the potential movement of contaminants by seepage of water from the tailings into the subtailings soil. This report presents various models of the movement of contaminants using both theoretical approaches and empirical evaluation of data available from other investigations. The data consist of field measurements and laboratory determinations of major and trace cations, the dominant anions, ph, eh, and specific conductance of solids and waters from the tailings and surroundings. Evaluation and interpretation of data were accomplished by using eh-ph diagrams, various statistical methods, and the wateqfc computer program. Data analysis shows that the critical area of investigating movements is the interfaces between tailings and the external environment. The chemical differences at interfaces seem to result in a sink system for contaminants. The tailings-soil-water system shows extreme complexities. The validity of the simplifying assumption used has been shown and increasing complexity has been built into the models.