CoMag® is a ballasted flocculation sedimentation process designed for different applications including tertiary phosphorus removal. The Town of Maynard selected the process to achieve an effluent phosphorus limit of less than 0.1 mg/l with the understanding that the future reductions in the permitted discharge could be implemented. Brown and Caldwell designed the process in concert with Cambridge Water Technology to enhance the design to suit the site limitations at the Maynard WWTP as well as to implement process modifications based on the operating experience of the first facility in Concord, Massachusetts. The design was able to achieve permit compliance immediately upon start up and showed an execellent ability to maintain performance during peak flows and even during high solids loads during plant upset conditions. The process has shown the ability to reliably meet effluent concentrations below 0.1 mg/l even without any additional downstream filtration.