One Little Paragraph…One Complicated Program: Monitoring Flows from a Separate Sanitary Sewer System to a Combined Sewer System

The Metropolitan St. Louis Sewer District (MSD) has entered into a consent decree (CD) which will require removing Constructed Sanitary Sewer Overflow (SSO’s) and managing Combined Sewer Overflows (CSO’s) in their 525 square mile collection system. In order to meet the requirements of the CD, MSD has launched a $4.7 billion, 23 year initiative to plan, design, and build system-wide improvements to address water quality and wet weather concerns effecting the collection system, which include a Capital Improvement and Replacement Program(CIRP), Capacity, Management, Operations, and Maintenance (CMOM) activities, I&I removal, and Green Infrastructure.The CD states, “MSD shall also provide in its Master Plan a flow monitoring plan and a list of locations of flow meters to be installed on the sanitary trunk sewers which convey major flow into the Combined Sewer System.” The CD also states, “In no case shall the complete and permanent removal or permanent abandonment of a Constructed SSO Outfall be designed to create a new Constructed SSO Outfall, require the physical modification of an existing Constructed SSO Outfall, or increase the frequency or volume of discharges from an existing Constructed SSO Outfall, known SSO, or CSO.” To summarize: The District must show that, by creating the projects in the CD, it isn’t simply moving the problems downstream from non-permitted SSOs to permitted CSOs. St. Louis MSD has developed a metering and data analysis plan to meet these requirements.