The City of Montreal, Quebec, is considering retrofitting its Atwater water treatment plant in the near future. The City has been actively involved in an effort to identify and define the design criteria of the most cost-effective treatment scenario to meet water quality goals. In a previous study, the use of ozonation was rejected and direct dual media biologically active filtration was identified as the most promising treatment process for the plant upgrade. This paper describes the results of testing undertaken to optimize filter performance for the removal of turbidity, particles and aerobic spore-forming bacteria, while meeting other water quality goals. The objectives of the study were to increase filter performance by modifying filter media and adding coagulation within the constraints of the existing facilities.