This report describes research on the European practice of preozonation of water to modify naturally occurring organics, followed by bacteria activated carbon (BAC) adsorption to remove trihalomethane precursors. A 100-gal/min pilot plant was designed, constructed and operated to evaluate this process on groundwater in Miami, FL. The raw groundwater feed is representative of sources that are heavily loaded with naturally occurring organics and some volatile chlorinated organics. The first pilot plant study evaluated removal of THMFP by ozone-anaerobic BAC vs. a control system fed nonozonated water. In the second pilot plant study the ozone and nonozone BAC adsorbers were oxygenated from initial startup. During both studies, a complete bacterial profile study was conducted to compare with conventional breakpoint chlorination performance. While the pilot plant was being constructed, and during its operation, bench-scale research was also conducted, including: (1) evaluation of GAC adsorptive capacity for THMFP and selected organic pollutants, (2) determination of the source of volatile chlorinated ethene compounds in the local groundwater, and (3) removal of volatile organic pollutants by aeration.