A Win for Clean Water: Improved CSO Tracking and Reporting

We are happy to report that an improved tracking and reporting system for combined sewer overflows in Alewife Brook and the Upper Mystic River basin is now in place. The conditions of this new variance, which were approved by MassDEP and adopted by the cities of Cambridge and Somerville, will help establish better water quality controls for the Mystic and allow for better transparency about untreated sewage entering our waterways. Yes, in this day and age we all still discharge sewage into our rivers through CSOs! 

So what are combined sewer overflows (aka “CSOs”) and why do we need to monitor them? In general, wastewater sewer and stormwater pipes are separate systems. Wastewater is directed to a wastewater treatment plant, while stormwater from roads is directed through storm drains and pipes to the nearest waterbody. However, in some older areas of urban systems there are combined sewers where stormwater from streets and wastewater from homes are sent in the same pipe to the wastewater treatment plant. Sewage makes it to the sewage treatment plant most of the time. But—during periods of heavy rainfall or snowmelt the amount of rain water in a combined sewer system can overwhelm the system and these systems are designed to overflow—instead of backing up into houses and streets—and discharge directly to nearby water bodies. These pipes emptying into rivers and streams are “combined sewer overflows,” or CSOs. CSOs typically occur during rainfall of more than one inch, and occur on both the Charles and Mystic Rivers.

The continued existence of CSOs definitely hurts water quality. The non-stellar grade of Alewife Brook in the annual EPA Mystic River Watershed Water Quality Report Card in part reflects this. But the infrastructure changes needed to get rid of CSOs entirely are hugely expensive (digging up streets, first of all). As a compromise, regulators allow some to continue, but subject them to improvements and strict monitoring. 

The City of Cambridge, we are pleased to say, has taken the lead in CSO management in recent years. Cambridge has spent more than $150 million over the past several years in separating stretches of combined sewer. The recent (and beautiful) stormwater wetland at Alewife Station is one result: newly created separate stormwater pipes drain here, where plants and soils act as a filter for some important stormwater pollutants. More recently, Cambridge has committed to new telemetry reporting from existing CSOs to better monitor performance and discharge volumes.   

This variance for Alewife Brook and the Upper Mystic River basin is a short-term modification of more stringent water quality standards and is intended to establish a baseline for appropriate water quality/CSO standards in the Mystic. The Massachusetts Water Resource Authority (MWRA) will be required to continue monitoring water quality at Alewife and the Mystic, and assess the level of CSO control achieved, the feasibility of better CSO control, and the water quality and public health impacts of CSOs. 

MWRA, along with the cities of Cambridge and Somerville, will be required to notify the public about any CSO discharges through permanent signs at outfalls, annual progress reports, public meetings and press releases, and a subscriber-based notification system. They are also required to inform the Mystic River Watershed Association (MyRWA) within 4 hours of each CSO discharge. You can find the EPA variance here

Right now there is no general public notification requirement for CSO discharges, but state legislation, which MyRWA has strongly supported, will ensure the public is notified within 2-hours of all CSO discharges. Real-time notification—within a few hours of discharge— is a win for public health, allowing people to make informed decisions around recreation. 

MyRWA has advocated for these variance conditions for years and provided recommendations during the variance review period. MyRWA currently coordinates a subscriber-based notification system for CSO discharges in the watershed, as we are alerted. To sign up, please send an email to contact@mysticriver.org. You can also learn about water quality and the probability of elevated bacteria levels due to CSOs using our Daily Boating Advisory website and by following our Twitter feed, @SafeMystic.