Evolution of the Private Inflow Reduction Process in St. Louis

PURPOSEThe purpose of this paper is to describe the process that the Metropolitan St. Louis Sewer District (MSD) has implemented to reduce stormwater inflow to the sanitary sewer through private property sources and highlight the lesson learned over the evolution of the program since 2003. The comprehensive Private Inflow Reduction (PIR) effort is an integral part, and perhaps the key to the overall success of 23-year, $4.7 billion Capital Improvement Program St. Louis MSD has undertaken.PROJECT BENEFITSThis project offers a new perspective on how to achieve inflow reduction through a cooperative approach between private property owners and the local sewer district. This paper will discuss how the St. Louis MSD has modified its approach to conducting PIR work through the integration of GIS in all aspects of the project in an effort to achieve 100% private property owner participation in reducing significant sources of inflow.St. Louis began their District-wide I/I program in 2003; this paper will highlight three projects which have been completed since then; Bellsworth Sanitary Relief, Hampton Creek CSO Separation and Glendale Section D Sanitary Relief, Inflow and Infiltration Reduction. Finally it will discuss the challenges faced as MSD moved to a District wide PIR Program. The majority of the PIR design phase to be completed in 2025 with construction wrapping up in the following year.TECHNICAL CONTENTIn 2013, the Metropolitan St. Louis Sewer District like many other cities entered into a consent decree to control sanitary sewer overflows, which dictates that the District address areas of excessive I/I. As the fourth largest sewer agency in the country, the District has implemented a large-scale I/I reduction program. This paper will discuss importance of I/I reduction efforts, focusing on sewer capacity and cost effectiveness as part of the $4.7 billion program to control sanitary sewer overflows.St. Louis began their I/I reduction program with individual projects utilizing clipboards and digital cameras. When evaluating a limited number of properties in individual project locations this process worked well. However as MSD transitioned to a large scale district wide program evaluating over 20,000 properties a year this process was archaic and time consuming. Recognizing the need for a massive data collection effort the process evolved to include 75+ personnel collecting and reviewing data using iPads and Mobile GIS.Results of the field investigation will be shared, elaborating on the three years since the inception of Project Clear, in which MSD and CDI has evaluated over 70,000 private properties for sources of private inflow. On these properties we have identified approximately 100,000 sources of inflow. During the course of these private property evaluations we have taken over 500,000 photographs, collected data points on over 300,000 topographic features, and made recommendations for stormwater separation to approximately 16,000 properties. According to our estimate, once these sources are eliminated nearly 250 acres of drainage area currently entering the separate sanitary sewer will be removed.