June 2012, Vol. 24, No.6


Sewer system evaluation tools available

U.S. EPA issues technical guides and computer tools for sewer condition and capacity assessment

Srini Vallabhaneni, Carl Chan, and Ari Selvakumar

The U.S. sanitary sewer infrastructure is aging. Some sewers are more than 100 years old. Nationwide, there are more than 19,500 municipal sanitary sewer collection systems serving an estimated 150 million people and about 40,000 sanitary sewer overflow (SSO) events per year. Addressing aging water infrastructure challenges is one of the top national water program priorities and a top priority of the U.S. Conference of Mayors (Washington, D.C.).

Rainfall-derived infiltration and inflow (RDII) into sanitary sewer systems has long been recognized in many sewer systems as a major cause of poor performance and operating problems, including SSOs. The extent of infiltration also correlates with the condition of aging sewers.


Technical reports and tools available for use

To assist communities in developing SSO mitigation plans, the U.S. Environmental Protection Agency (EPA) in 2002 entered into a cooperative research and development agreement with CDM Smith (Cambridge, Mass.) to develop an easy-to-use public domain set of computerized tools and associated technical guides. The set of tools is referred to as the SSO Analysis and Planning (SSOAP) toolbox.

Review of Sewer Design Criteria and RDII Prediction Methods . This technical report (EPA/600/R-08/010) summarizes EPA’s review of prevailing industry practices for RDII prediction and selected methods that are proven for a range of application needs. In addition, it describes the specific RDII prediction methodology used in the initial version of the SSOAP toolbox.

Computer Tools for Sanitary Sewer System Capacity Analysis and Planning . This report (EPA/600/R-07/111) is intended to provide SSOAP toolbox users with technical information needed to effectively use the toolbox to analyze and mitigate SSO-related problems. The technical report provides an introductory hydrologic approach, the RDII methodology used in the toolbox, an overview of the required sewer system hydraulic analysis, and data collection requirements to support SSO planning and analysis using the toolbox. In addition, the report describes the tools and their functions for performing a wastewater collection system capacity and condition assessment.

The report also includes a description of EPA’s Storm Water Management Model software application within the SSOAP toolbox for assessing the baseline hydraulic conditions of the system and quantifying capacity improvements of various identified improvement scenarios. Guidance is provided for establishing improvement objectives, screening potential options, and developing scenarios. Finally, the report provides a case study that demonstrates how the methodologies described in this technical report have been used in SSO mitigation planning.

Software tools. The SSOAP toolbox contains a suite of integrated computer software tools that can serve as the foundation of wastewater collection system engineering, operation, and maintenance assessments. The toolbox can be used to manage large rainfall and flow-monitoring databases, analyze flow data, apply the results to perform capacity analyses, prioritize where to conduct field investigations to assess sewer condition, suggest subsequent sewer rehabilitation projects, and assess the performance of rehabilitation programs.

In addition, the toolbox and technical guides will support EPA program offices in conducting capacity, operation, and maintenance requirements for National Pollutant Discharge Elimination System permits. This, in turn, helps municipalities identify SSO problems and develop sensible control plans to meet their permit requirements.


SSOAP training workshops, users support, and software updates

In addition to these tools, EPA, through contractual services provided by CDM Smith, has been providing SSOAP toolbox users with support and conducting training workshops for EPA program offices, regions, states, and municipalities nationwide.

User support has included software installation, data input, parameter definition, software operation, and output interpretation. Since the original 2009 release, minor updates to the SSOAP software (versions 1.0.1, 1.0.2, and 1.0.3) have been released. These updates were based on user feedback.


Ongoing enhancements and technical guide development

The SSOAP toolbox is being enhanced in relation to EPA’s research on aging water infrastructure. Assessing sewer systems currently relies on visual examination using time-consuming, expensive field investigations, such as conventional closed-circuit television or emerging technologies (e.g., sonar, laser, ultrasonic, and infrared). The RDII prediction methodology employed in the SSOAP toolbox can help to design a focused condition assessment program and maximize the success of field investigation efforts. The RDII methodology also provides an effective means to assess the post-rehabilitation performance of the sewer system using the pre- and post-rehabilitation programs.

The current features in the SSOAP toolbox enable users to extract needed information and use external tools to support these condition assessment activities, as well as post-rehabilitation assessments. However, EPA determined that more integrated features within the SSOAP toolbox are beneficial to the user community to support these critical sewer assessments. The enhancements planned through June 2012 include streamlining the current features with creation of a dedicated new tool, the Condition Assessment Support Tool. The primary objectives for these enhancements are to develop priorities among different sewersheds and subsewersheds for designing a focused field investigation plan and subsequent sewer rehabilitation plan, and assess the effectiveness of sewer rehabilitation programs using pre- and post-rehabilitation RDII correlations.

This additional tool in the SSOAP toolbox will enable users to perform efficient data synthesis and offer a direct way to establish focused field investigations and, therefore, cost-effectively conduct successful condition assessment programs. A major update to the SSOAP toolbox (version 2.0.0) with this additional tool is anticipated this fall. A case study publication also is being developed to demonstrate how the enhanced SSOAP toolbox was applied in a sewer condition assessment and rehabilitation program.


Srini Vallabhaneni is an associate, and Carl Chan is a water resources engineer in the Indianapolis office of CDM Smith (Cambridge, Mass). Ari Selvakumar is an environmental engineer in the U.S. Environmental Protection Agency Office of Research and Development, National Risk Management Research Laboratory, Water Supply and Water Resources Division, Urban Watershed Management Branch, in Edison, N.J. 

For more information or to download the software, visit the SSOAP toolbox website, www.epa.gov/nrmrl/wswrd/wq/models/ssoap.  


©2012 Water Environment Federation. All rights reserved.