Experiments with alum under adsorption—charge neutralization destabi1ization conditions (pH=6.0) were conducted to investigate ozone trends under water treatment conditions. The objectives of this research are as follow: • Quantify the effect of various levels of humic material on the stability of alumina particles at pH=7.5. This extends the work of Felix—Filho (1985) and tests the hypothesis of Davis (1980) that under conditions typical of natural waters, only small amounts of dissolved organic carbon adsorb to suspended particles, yet this organic material may significantly influence surface properties of particles, such as surface charge and colloidal stability. • Evaluate the effect of Ca2+ on the stability of alumina particles equilibrated with solutions of calcium and humic material. This extends the work of Ali et al (1984), who demonstrated that higher levels of calcium in lakes may result in increased rates of particle aggregation. • Test the effect of calcium and humic material on the susceptibility of alumina particles to ozone-induced microflocculation. This extends the work of Felix-Filho (1985) and provides for the laboratory testing of an apparent trend in the literature of raw waters of higher calcium hardness demonstrating a higher susceptibility to ozone—induced microflocculation. • Measure the electrophoretic mobility (EPM) of all suspensions to allow a comparison of this surrogate measure of particle stability to rigorous measurements of changes in the particle size distribution with time. • Test a mathematical model for particle aggregation using the Smoluchowski equation. Test the ability of this model to describe particle aggregation for varied solution chemistries representative of natural waters.