Managing Sanitary Sewer Overflows (SSOs)

The U.S. EPA estimates that approximately 23,000 to 75,000 sanitary sewer overflows (SSOs) occur in the United States each year. An SSO is defined by the release of untreated sewage into the environment through an overflow, spill, basement backup, or unpermitted discharge before completed treatment at the sewage plant. These overflows can degrade water quality, cause property damage, and pose serious threats to public and environmental health due to the release of harmful pollutants, disease causing microorganisms, metals, and nutrients into the environment. 

Section 301 of the Clean Water Act prohibits the discharge of pollutants to any Water of the United States from a point source without a National Pollutant Discharge Elimination System (NPDES) permit. To address compliance challenges associated with SSOs, the EPA recently completed a National Compliance Initiative that first began in 2000 to reduce the discharge of raw sewage in national water ways.

SSOs occur through debris or grease blockages, root intrusion, vandalism, inflow and infiltration, improper design, aging infrastructure, operational mistakes, and structural, mechanical, or electrical failures. Typically, the most frequent culprit takes the form of blockages. After an overflow, clean up and response is not only expensive, but traumatic for the impacted communities.

In Queens, NY a sewage backup on the Thanksgiving holiday weekend of 2019 flooded the basements of approximately 100 homeowners creating a putrid odor and exposing the community to harmful pathogens. Liability for residential damages and repairs to the pipe was projected to reach millions of dollars.  The culprit for the backup? While operators initially theorized a grease induced fatberg was to blame, investigation later revealed a collapsed sewer pipe instigated the SSO.

In New England and around the country, many communities maintain collection systems of 100 years old or more. Aging infrastructure exacerbates SSO prevention challenges. As years of wear on system equipment increases, the likelihood of mechanical or electrical failures as well as the opportunity for inflow and infiltration increases. Pipe deterioration due to natural freeze-thaw cycles, environmental conditions, water flow, and water chemistry can also increase the likelihood of structural failures. When this deterioration is not routinely inspected and maintained, resulting failures will only add further hydraulic stress to the system.

The frequency of SSOs can be reduced significantly through preventative maintenance and the implementation of an appropriate asset management program. To upgrade your preventative maintenance program, an article from the March 2017 Kansas Lifeline discusses the basics of lift station maintenance. The Georgia Association of Water Professionals provides a more comprehensive guide of collection system maintenance practices in its 2016 guide Wastewater Collection System Best Management Practices.

Developing an asset management program will allow systems to plan for the replacement or rehabilitation of aging pipes, pumps stations, valves, manholes, and collection system infrastructure. During program development systems can predict and plan for population changes, capacity objectives, equipment deterioration, and more. To encourage proper asset management of collection systems, the EPA developed the CMOM program. CMOM stands for Capacity, Management, Operations, and Maintenance.  The information-based management approach encourages dynamic collection system management through the prioritization of activities and investments. Utilities can access how well their current practices meet the CMOM framework using this Self Assessment Checklist and the EPA Evaluation Guide for CMOM at Sanitary Sewer Collection Systems. Follow up this evaluation by integrating CMOM best practices into a new or updated asset management program using this blog post.

Even with the implementation of these programs, systems should still prepare for the event of an unexpected overflow. As in Queens, NY, preventative maintenance and asset management did not stop the SSO on the Thanksgiving weekend. Systems must be prepared to respond swiftly with a Sanitary Sewer Overflow Response Plan. These emergency response plans will limit potential damages and reduce community distress. By combining preventative maintenance, asset management, and emergency response planning, systems can ensure that their community and its environment have the best protection from SSOs.