Investigating I/I into a Collection System with a Network of 87 Pump Stations Using SCADA Data

Overview: This presentation will describe the approach and share the results of an analysis performed to quantify dry weather flows (DWF) and rainfall derived inflow and infiltration (RDII) into a manifold sanitary sewer force main system with 87 contributing pump stations. The presentation will detail a method of analyzing pump station inflows without the need for installation of expensive flow meters upstream of every pump station in a collection system. The approach also allows for evaluation of historical storms that may have been the catalyst for system-wide assessments prior to any flow metering or other hydraulic assessment plans or studies.

Approach and Current Status: This approach utilizes existing SCADA sensors and data loggers installed in pump stations and transforms pump startup/shutoff activity into a contiguous dataset of inflow rates based on wet well geometry and pump operational envelopes as depicted in Figure 1. This flow data can then be used to analyze DWF diurnal patterns and magnitudes as well as timing and magnitude of any wet weather responses. This data can, in turn, be used to assess performance at individual pump stations in support of a system-wide sanitary sewer master plan update. This approach has been used to develop an updated sanitary sewer system master plan and create a short list of system improvements and capital improvement projects. Key projects from this updated plan have already started detailed design and critical projects are expected to be completed by 2022. This method will also be used to assess pre and post construction I/I and pump station performance.

Results and Benefits: SCADA information was successfully transformed from inconsistent on/off recordings into a contiguous flow hydrograph, as depicted in Figure 2. By analyzing all pump station performance throughout the system holistically, a more complete assessment of system-wide hydraulic performance can be achieved without exorbitant costs supporting system studies, which reserves budget for physical system enhancements. As part of a master plan update, this approach has been employed to economically assess performance of pump stations under existing conditions by simulating a variety of actual and synthetic rainfall conditions. These assessments of individual pump station capacity limitations, force main velocity and head loss performance, and water reclamation facility inflows under both existing conditions and future expected population growth and land development were then used to create an updated sanitary sewer master plan. This plan was executed for a fraction of the cost of a plan with a comprehensive flow metering network.

Conclusion: Using SCADA data is an economical way to analyze actual system performance, assess individual pump station or system capacity, update and recalibrate hydraulic models, and develop potential improvements for sanitary sewer collection systems with any number of pump stations. The approach described in this presentation was executed for a fraction of the cost of a plan with a comprehensive flow metering network installed in gravity sewers and was applied successfully to a collection system with 87 individual pump stations.