The 75 MGD Little Falls Water Treatment Plant in Totowa, New Jersey, required process improvements to enable it to meet the Stage 2 D/DBP regulations as well as other long term raw water quality problems. The source water originates in forested watersheds, but also receives numerous wastewater discharges upstream from the plant intake. Because this is an urban watershed, the raw water quality can vary considerably from month to month, day to day, and at times even hour to hour. Principal contaminants of concern are disinfection byproduct precursors, pathogenic organisms, turbidity, algae, taste and odor, organic compounds, iron and manganese, and nutrients. The retrofit design was developed to maximize the utility of both existing and new treatment facilities within the limited site. A major change is the use of a compact ballasted flocculation system to replace the function of the existing sedimentation basins. This is the largest (120 MGD) ballasted flocculation potable water plant in the United States. In addition, ozone will be applied to meet the full range of oxidation and disinfection goals for the project and is followed by deep bed biological filtration. As part of the design scope of this upgrade, the Black & Veatch/Hatch Mott MacDonald team designed, constructed, and operated a 0.2 mgd Actiflo pilot plant at 30 gpm/sq. ft. and as high as 42 gpm/sq. ft. Additionally, the pilot facility was equipped with an ozone contactor and biological filters. The paper discusses the successful optimization of the ballasted flocculation process for the removal of turbidity with respect to polymer, microsand size, and coagulant. Demonstration testing was performed in 2001 and side-by-side comparison studies with the full-scale facility were performed in 2003. The evaluation determined that the pilot facility underestimated turbidity removal and required greater polymer and coagulant doses. The pilot facility is currently being used to optimize the full-scale for economical operations and as an indicator for changes in water quality that require modifications to plant operation. Includes tables, figures.