Assessing Combined Sewer Systems Vulnerability to Sea Level Rise

Many combined sewer overflow (CSO) outfalls in the estuary are already fully or partially submerged during high tides, requiring installation of special valves and even pumping. With sea levels rising rapidly, understanding the vulnerability of CSO infrastructure and assessing possible remedies was the subject of a recent effort by the New York-New Jersey Harbor & Estuary Program (HEP) and the U.S. Environmental Protection Agency (EPA) in New Jersey. HEP’s workshops, as well as the upcoming final report, provides important examples and guidance for managers and engineering professionals seeking to create climate-ready water systems.

Sea level has been rising for decades, and a warming planet will accelerate this phenomenon. The State of New Jersey projects that mean sea level will be two feet higher by 2050. The functioning of combined sewer systems will be directly affected. This looming issue will compound the existing challenge of reducing the number and volume of discharges from combined sewers, which occur when sewage treatment plants reach capacity during storms. To understand the magnitude of these issues and better prepare for the future, HEP and EPA partnered with two New Jersey municipalities, the City of Elizabeth and the Village of Ridgefield Park, to assess the risk of sea level rise impacts to their respective CSO outfalls. The project relied on EPA’s Climate Resilience Evaluation and Awareness Tool (CREAT), a risk assessment application that helps municipalities and utilities adapt to sea level rise and extreme weather events by better understanding climate change resiliency and risk reduction when it comes to addressing CSOs.

On July 27th and July 29th, HEP and EPA held a virtual workshop for engineers and CSO permit holders in New Jersey and New York. Over the course of two days, speakers from the EPA and their consultants at the Cadmus Group provided an overview of the tool’s purpose and applications, while representatives from municipal engineers at Mott MacDonald shared their experiences working through the tool for two New Jersey CSO municipalities, the Village of Ridgefield Park and the City of Elizabeth. Panelists from Cadmus, CDM Smith, and EPA also provided attendees with a few case studies to illustrate how CREAT can be applied in other contexts. The workshops concluded with a walk through of the main content-driven modules of CREAT, with special attention paid to the definition of threats and assets, the development of adaptation plans, and the interpretation of the results of the risk assessment.

Both representatives from Mott MacDonald shared their retrospective evaluation of CREAT’s usefulness for the two municipalities and how the tool helps to incorporate climate change resiliency and risk reduction into the Long Term Control Plan process. CREAT serves as a valuable sensitivity analysis for investigating extreme weather and sea level rise scenarios while also identifying and quantifying their potential impacts.

The two-day virtual workshops were recorded and are now available on HEP’s website. HEP will be working with the project partners to prepare and deliver a final report outlining the project’s findings this fall.