Wednesday, May 22, 2024

The mouth of Alewife Brook at the Mystic River in 2017. (Photo: Magicpiano via Wikimedia Commons)

As global warming brings more intense rainstorms and increased threat of flooding and sewage overflows into the Alewife Brook and Charles and Mystic rivers, Cambridge, Somerville and the MWRA have asked for a three-year extension on an overflow-prevention plan.

The initial schedule was to have a draft plan by June 2023 and a final plan by December 2023.

Residents from more than a half-dozen communities learned of the new timeline at a Dec. 15 virtual meeting organized by the two city governments and Massachusetts Water Resources Authority.

A delay allows for more public input and ensures “we’ve had enough time for thorough alternative development and analysis,” said Brian Kubaska, assistant director of engineering at the MWRA.

In part that’s needed because the state and federal environmental regulatory agencies – the Environmental Protection Agency in particular – are “pushing us to consider climate change” in plans to prevent sewer overflow, “yet not really providing any guidance,” said Kathy Watkins, Cambridge’s commissioner of Public Works.

Most U.S. sewer systems have dedicated, separated networks of pipes – one for sewage and one for stormwater. That’s true for only about 5 percent to 10 percent of Somerville and 60 percent of Cambridge, which means excess flow from very heavy rainstorms can overwhelm the city’s system and cause combined sewer overflows into the Alewife, Charles and Mystic that contain bacteria, nutrients and other pollutants. That means debris, oil slicks, odors and other water quality impacts in the waterways, said officials at the virtual meeting.

A plan developed for Greater Boston in the late 1990s that cost more than a billion dollars “got us a long way” toward fixing the problem, with annual CSO volumes reduced by 87 percent, or a 2.8 billion-gallon-per-year reduction, Kubaska said. “Our work isn’t done.”

Fifty million gallons of sewage-contaminated stormwater were discharged into the Alewife Brook from the cities of Cambridge and Somerville in 2021. There was as much sewage-contaminated water discharged into the Alewife Brook last year as in 1997, before the implementation of a $200 million plan to modernize the area’s antique combined sewer systems.

Innovating alone

Now, Cambridge, Somerville and the MWRA – tasked jointly with developing a new control plan – find themselves largely on their own.

“We’re not aware of any CSO plan across the country that has incorporated climate change. [The Department of Environmental Protection] and EPA do not have any standards … and no direction on how to incorporate climate change,” Watkins said. “Since it’s never been done, it has been a tremendous amount of work and effort.”

The planners enlisted help from Indrani Ghosh, a senior climate resilience specialist at the environmental engineering firm Weston & Sampson who has led several regional and state climate resiliency projects.

The work has meant innovating a data-driven development of a “typical year” that considers rainfall projections from climate change scenarios – a rigorous and extensive technical analysis that was peer reviewed by leading climate experts, Ghosh said. Computer modeling will determine the level of overflows to be expected over the coming years, creating a baseline to predict and analyze future conditions.

“A necessary evil”

Sewage shoots out of the ground in Roswell, Georgia, in September 2009 in an image from a Dec. 15 presentation by Cambridge, Somerville and MWRA representatives.

In Cambridge and Somerville, sanitary flows and stormwater runoff all go together to Deer Island for treatment. But during very heavy rainstorms, excess flow can overwhelm the system and cause CSOs.

“Why do we permit combined sewer overflows at all? The simple answer is that they are a necessary evil,” said Rich Raiche, Somerville’s director of infrastructure and asset management.

If stressed systems didn’t have “controlled relief at known locations” and dump into brooks and rivers, there would instead be sewer overflows in residential areas. “Backups can discharge directly into basements and garden-level apartments, causing property damage and very acute health risks,” Raiche said. “No one at Cambridge, Somerville or the MWRA thinks that dumping raw sewage or any other form of pollution into the Alewife, Charles or Mystic is a good thing. We are all committed to improving our systems, reducing pollution and improving quality of life.”

Holistic approach

Cambridge and Somerville have additional responsibilities to their sewer customers, though.

“What’s bringing us to the table is the CSO issue, but we do have to look at our system improvements holistically,” Raiche said. “Cambridge has been on that path for at least two decades that I’m aware of – because I’ve been in the consulting world and have worked for Cambridge for the past two decades. Somerville has really started to focus on that within the past five, and we have done more construction in the past five years and have more plans for the next year than the previous 75 combined. So there’s a huge commitment at all levels here.”

There will be up to seven public meetings on major milestones – this is the second – as well as flyers, fact sheets and stakeholder interviews over the course of the three-year extension, Kubaska said. Residents of Cambridge, Somerville and surrounding communities are invited to take a survey about the CSO issue by Jan. 5.

“I hope people really do understand the level of effort and commitment and creativity that’s really been involved in how to effectively incorporate climate change into this process,” Watkins said. “That is a substantial commitment and really a completely new way of doing this.”

A version of this story appeared on the Somerville Wire.