The general objective of this project was to investigate the combined use and effectiveness of ozonation and biofiltration as a treatment strategy for reducing TOC levels in finished drinking waters. Four NOM sources were selected to represent a broad spectrum of compositions that might be encountered in drinking water supplies. The specific objectives of the project included: evaluate TOC biodegradation potential of the different sources of NOM; determine the benefits of ozonation to enhance TOC biodegradation and microbial activity; and investigate the factors controlling TOC biodegradation in a sand biofilter under conditions simulating conventional water treatment. Batch and biofiltration studies were conducted with the different NOM sources to address these objectives.