Burns & McDonnell performed a three-phase project to develop a system improvement plan for the separate sanitary sewer systems that serve 1.1 million people in the St. Louis metropolitan area. Phase I of this project involved the initial data collection and setup of “broad brush” hydraulic models of the trunk sewer, including major laterals up to all known overflow locations. Phase II involved selective data collection and development of “lateral-specific” hydraulic models. Phase III involved refining the calibration on the previously completed hydraulic models and the development of a final system improvement plan to address the deficiencies identified by the modeling effort.
This project phasing approach allowed Burns & McDonnell to limit the work effort to the critical parts of the collection system, as well as adjust the direction of the project in response to the Environmental Protection Agency's (EPA’s) development of the proposed Sanitary Sewer Overflow Control Policy.
- Development of sanitary sewer overflow control plan
- Monitoring and hydraulic modeling
The scope of work for Phase I involved the collection of the data necessary to develop the hydraulic models. Burns & McDonnell, in coordination with its subconsultants, has collected flow monitoring data from over 250 locations throughout the St. Louis area. In addition, rainfall data has been collected from 30 rain gauges, groundwater level data has been collected from more than 40 piezometers, survey data has been collected to verify system characteristics and sanitary sewer overflow samples have been collected to characterize overflow water quality. This data was used in conjunction with the existing Metropolitan St. Louis Sewer District (MSD) mapping information to develop the “broad brush” hydraulic models of the collection system.
Phase II work activities involved the collection of selected amounts of additional data to supplement the data collected in Phase I. With this additional data, Burns & McDonnell refined the calibration on the “broad brush” hydraulic model and also developed a hydraulic model of each major lateral tributary to the trunk sewer. These smaller, more detailed models were used to supplement MSD’s engineering design calculations and for MSD review of other consultant’s design efforts.
Phase III scope focused on the development of a system improvement plan (SIP). The results of the modeling effort were used to identify the improvements to the collection system to handle peak flows for future scenarios. The recommended improvements included upsizing and/or paralleling the pipes in the existing collection system, upgrading pump stations, upgrading head works at the treatment facilities, operational and maintenance protocol adjustments.