Sanitary Sewer Overflow Analysis and Planning (SSOAP) Toolbox
- Release History
Rainfall-derived infiltration and inflow (RDII) is the increased portion of water flow that occurs during a rainfall or snowmelt event. RDII has long been recognized as a source of operating problems in sanitary sewer systems. RDII is the main cause of sanitary sewer overflows (SSOs) to
- streets, or
- nearby receiving waters.
It can also cause serious operating problems at wastewater treatment facilities. There is a need to develop methodologies and computer tools to assist communities in developing an optimal capital improvement program. And also provides flexibility for future improvements.
The SSOAP toolbox is a suite of computer software tools used for quantification of RDII and help capacity analysis of sanitary sewer systems. This toolbox includes USEPA Storm Water Management Model Version 5 (SWMM5) for performing dynamic routing of flows through the sanitary sewer systems.
The SSOAP toolbox was developed from a cooperative research and development agreement (CRADA) with Camp Dresser & McKee Inc., (CDM), a global consulting, engineering, construction, and operations firm.
SSOAP uses the synthetic unit hydrograph (SUH) approach for predicting RDII. Specifically, this approach employs the RTK method to characterize the RDII response to a rainfall event. The selection of this method for quantifying RDII in the SSOAP toolbox is documented in the USEPA. "Review of Sewer Design Criteria and RDII Prediction Methods. (PDF)" (30pp, 186 KB)
The RTK method is probably the most popular SUH method. This method is based on fitting up to three triangular unit hydrographs to an observed RDII hydrograph shown above to estimate the fast, medium, and slow RDII responses. The Ri parameter is the fraction of rainfall volume entering the sewer system as RDII, Ti is the time to peak, and Ki is the ratio of time of recession to Ti. The RDII volumes of three unit hydrographs are designated as R1, R2, and R3. A high R1 value indicates that the RDII is primarily inflow driven. If more of the total R value is allocated to R2 and R3, this will indicate that the RDII is primarily infiltration driven.
The capabilities in the SSOAP toolbox are fully documented in the USEPA report “Computer Tools for Sanitary Sewer System Capacity Analysis and Planning (PDF).” (104 pp, 3.7 Mb). The SSOAP toolbox integrates databases of a sanitary sewer system and contains the following five functional tools for assessing the conveyance capacity of a sanitary sewer system:
Database management tool (DMT) – serves as the command center of the toolbox. It provides interface with several data sources (sewer systems, flow, and rainfall data), and interacts with other SSOAP tools and exchanges data. It stores and organizes data using a standard Microsoft Access® database called SSOAP System Database. To facilitate the data management function, the DMT includes software to:
- perform rainfall and flow data quality control;
- identify wet-weather events and determine rainfall volume, peak rainfall intensity, and antecedent moisture conditions; and
- support sanitary sewer system capacity analysis and planning.
The integration of these tools improves the efficiency and results of comprehensive data reviews.
RDII analysis tool – performs wastewater hydrograph decomposition and determines up to three sets of RDII parameters (Ri, Ti, and Ki). This tool performs:
- dry weather flow (DWF) analysis to develop from the flow and rainfall monitoring data, representative weekday and weekend DWF hydrographs at each metered station, including a determination of individual base wastewater flow and groundwater infiltration (GWI);
- wet weather flow analysis to determine the RDII hydrograph for a storm event by subtracting the DWF hydrograph and GWI adjustment flow from the total monitored hydrograph (the GWI rates prior to a rainfall event usually need adjustment to account for seasonal variations);
- unit hydrograph curve fitting analysis to determine Ri, Ti, Ki values by adjusting the Ri, Ti, Ki parameters for each event analyzed so that, when these values are applied to the monitored precipitation data, the simulated RDII reasonably matches the monitored flow; and
- statistical analysis of RDII parameters to extrapolate Ri, Ti, Ki unit hydrograph parameters from measured conditions to non-measured or design storm conditions.
RDII hydrograph generation tool – generates the RDII hydrograph of a sewershed for the selected rainfall events using its physical characteristics (e.g., sewer areas and land uses) and the Ri, Ti, Ki values determined. This tool can export RDII hydrographs to other hydraulic routing engines in addition to SWMM5.
SWMM interfacing tool – assists users in organizing and incorporating the hydrographs generated by the RDII hydrograph generation tool into the SWMM 5 input files.
SWMM5 Tool – performs the actual dynamic flow routing through a sewer network system and uses the graphic utility interface capability in SWMM5 to visualize the sewer system responses and selectively exports the output data for further analysis. Information on SWMM5 Tool.
The SSOAP toolbox is designed to support SSO mitigation efforts which include:
- Determining RDII characteristics
- Prioritizing sewersheds for sewer condition assessment, sewer rehabilitation and RDII source reduction
- Evaluating performance of sewer improvements based on RDII reduction
- Evaluating RDII related sanitary sewer overflows (SSOs) using SWMM5
- Managing SWMM5 hydraulic simulation results
- Managing and analyzing flow monitoring and rainfall data
USEPA will provide technical support to users through a contractor for a period of time governed by the availability of funds. Informational and/or hands-on training workshops at selected regions are being planned.
|Setup (EXE) (11 MB)||
|Release Notes (PDF) (2 pp, 128 KB)||January 2012|
- US EPA. (2007) "Computer Tools for Sanitary Sewer System Capacity Analysis and Planning. "(PDF) (104 pp, 3.53 MB)Publication No. EPA/600/R-07/111.
- US EPA. (2008)"Review of Sewer Design Criteria and RDII Prediction Methods." (PDF) (30 pp, 186 KB) Publication No. EPA/600/R-08/010.