St. Louis Lemay Sanitary Sewer Improvements

Client: Metropolitan St. Louis Sewer District
Completion Date: 2033
Location: St. Louis, Missouri


The St. Louis Metropolitan Sewer District (MSD) provides wastewater and stormwater service to approximately 1.4 million people in a 535-square-mile service area encompassing the city and county of St. Louis. The MSD wastewater collection system is the fourth largest in the United States, with more than 9,600 miles of pipe. Most customers are served by separate sanitary and storm sewers, although about 75 square miles of St. Louis City and adjacent areas in the county are served by a combined sewer system. Portions of the separate sewer system also experience high levels of infiltration and inflow (I/I) during wet weather. During heavy rainfall, the combination of storm water or I/I and wastewater may exceed the capacity of the sewer system resulting in combined sewer overflows (CSOs) or separate sewer overflows (SSOs). 

MSD is implementing a long-term control plan (LTCP) to eliminate all CSOs and SSOs during a 23-year period as part of a consent agreement with the EPA. MSD is expediting project delivery throughout its service area by contracting with watershed consultants to design various infrastructure improvement projects. The district hired Burns & McDonnell as the watershed consultant for the Lemay Watershed. Our team is providing design and engineering services during construction to implement MSD’s LTCP and SSO control plan. More than 70 projects will be designed during a 5- to 10-year period. The Lemay Service Area covers nearly 119 square miles in the City of St. Louis and a portion of St. Louis County west and south of the city. The program comprises four watersheds within the Lemay Service Area, including Gravois Creek, Mackenzie Creek, Martigney Creek and University City. Some areas are served by combined sewers while others are served by separate sanitary and storm sewers. Wastewater treatment is provided at the Lemay Wastewater Treatment Facility.

The project scope includes review and evaluation of sewer sizes, recommended alignments and lengths, including hydraulic analysis and design assumptions, as well as private inflow reduction (PIR), and preliminary studies for some projects. Wet weather storage facilities and pump stations will be constructed to handle peak flows during storm events. Storage facilities may be above or below ground and will be designed to blend in with the surrounding area. The storage facilities will be equipped with automatic controls for filling, emptying and flushing as well as remote operation via MSD’s SCADA system. 

Sanitary replacement and relief sewers will be designed to augment existing sewers or replace undersized/deteriorated sewers. Due to the highly developed nature of the project area, alignments must be carefully selected to avoid disruption of existing homes, commercial buildings, roadways and utilities. Coordination with utilities will be critical since proposed corridors are shared by multiple facilities. Public I/I reduction, consisting largely of CIPP sewer lining, will be performed. Private I/I sources such as downspouts and area drains, will be disconnected throughout the service area to reduce the load on the sewer system. 

Our full team includes a total of 17 firms providing specialty services related to surveying, geotechnical, hydraulic modeling, storage facility design, public and private I/I removal. Coordinating and managing such a large program with numerous stakeholders will involve the use of web-based collaboration tools and a suite of project management and scheduling software. Regular reporting and communication with EPA and MDNR will be performed to ensure the program stays on track and meets the consent decree requirements. A community-wide public involvement program is a key part of the project to keep residents informed and obtain buy-in and feedback.


  • Consent degree-driven, 23-year LTCP program
  • Preliminary studies
  • Field investigations
  • Hydraulic modeling
  • Public and private inflow removal