[en] Reinjection of treated groundwater from the F-Area and H-Area seepage basins may produce conditions where stable colloidal suspensions are generated that lead to permeability reductions in receiving zones in the aquifer or to anomalously high concentrations of particulates in monitoring well samples. In order to determine the conditions under which stable colloids are generated in Savannah River Site (SRS) sediments, the Savannah River Ecology Laboratory (SREL) and the University of Georgia (UGA) undertook bulk dispersibility and column experiments. The sediments used are representative of the natural matrix materials in the upper most aquifers in the general separations area. The study indicated that the sediment surfaces are sensitive to slight charges in solution chemistry and that outside the natural range of pH conditions, stable colloids are generated. At low pH values, positive-charged dilute colloidal suspensions are formed, whereas at high pH values, combined with high sodium adsorption ratios, more turbid suspensions are formed that are capable of causing receiving zone clogging. In dilute, poorly buffered solutions, ion exchange reactions influence the pH of the solutions and changes up to 1 pH unit were observed as a result of these reactions. The direction and magnitude of the solution pH change was predictable and dependent on the species of cations and anion in the simulated injectate. Recommendations for maintaining capability between the receiving sediments and the injection waters include maintaining the pH of the water between 5.5 to 6.5, maintaining a balance between ''acidogenic'' and ''alkalinogenic'' ions to stabilize the pH, and maintaining a low to moderately low ionic strength