This project was conducted on both a pilot and laboratory scale to understand the effects of ozonation and the relationship between adsorption and biological activity during water treatment with ozone and granular activated carbon. The removal of trace organic substances of health concern at the ng/L to micrograms/L level and the removal of Total Organic Carbon at the mg/L level were carefully monitored along with microbial parameters of biological speciation and growth rate. This report summarizes the results of chemical (inorganic and organic) and microbiological analyses and evaluates the performance of pilot plant schemes for granular activated treatment at Philadelphia. System comparisons were made using estimated total costs of each unit process, as determined by the carbon reactivation rate needed to maintain various effluent criteria.