MLE Process Plus Flow Blending for CSO Flows

Combined sewer overflows (CSOs) are gaining the attention of environmentalists and regulators. Communities are taking steps to decrease the number of overflow events and to reduce the amount of pollutants discharged in these events. Like most communities in the Northwest, Mount Vernon, Washington, has a mandate to reduce CSOs to less than one event per year. Engineers, regulators, and City staff members investigated cost-effective means to implement CSO reduction programs. This paper summarizes the cost-effective CSO reduction program implemented by the City of Mount Vernon. The program involves storage, treatment, and blending as methods to achieve the desired level of less than one CSO event on average per year.