CSO’s in the Merrimack River
We experienced the worst year on record for Combined Sewage Overflow (CSO) events in the Merrimack River in 2023, with over 2 billion gallons of sewage being discharged into the river, toppling the previous record of ~ 800 million gallons. In light of this record-breaking year, and the increased exposure river users have to interact with contaminated water during CSO events, MVPC is sharing a series of posts about CSOs, including what CSO events are, how you can be safe during these events, and measures MVPC is taking to increase awareness and safety when interacting with the river. To find out more about CSO events in the Merrimack River during 2023, check out our CSO Frequently Asked Questions (FAQ) below, read our previous articles, or email [email protected].
CSO FAQs
What is a Combined Sewer System?
A combined sewer system is a sewage system where all wastewater, including household sewage, rainwater runoff, and industrial waste, gets collected into one pipe that leads to a wastewater treatment plant. When this system is overwhelmed by heavy rainfall, the wastewater is discharged into a nearby body of water – in our case, this is the Merrimack River.
What are CSOs?
CSOs occur when there is heavy rainfall, causing the sewage system to get overwhelmed. The combined volume of the rainwater and sewage exceeds the system capacity, leading the untreated stormwater and wastewater to discharge into the river. The Merrimack River has three CSO event locations in Massachusetts alone.
Why should we care about CSOs?
CSOs release high levels of bacteria into nearby water bodies that can lead to increased health risks. With climate change, heavy rainfall events are becoming more common, making CSOs an even bigger challenge for the river and those who interact with it.
How do CSOs impact us?
CSOs cause the bacteria concentration in the water to reach dangerously high levels. When this occurs, it is unsafe to interact with the river due to increased health risks caused by the bacteria. According to a report published by the EPA, when people come in contact with CSO water they may contract bacterial infections that can cause fever, diarrhea, vomiting, and ear infections. It is also possible to get parasitic infections including tapeworms, hookworms, and whipworms.
How will I know if a CSO has occurred?
If there is heavy rainfall in your area, there is a high chance that a CSO event has occurred. For more information, you can sign up for notifications from your local wastewater treatment plant. MVPC is also working to release a real time predictive dashboard that will tell you the bacteria levels in the water and estimate risk level. This dashboard will be released later this spring. Stay tuned for more information!
How long do the negative effects of a CSO event last?
Bacteria levels in the river are typically hazardous for 48 hours, but can be unsafe for up to 3 days.
How can I be safe after a CSO event has occurred?
The high bacteria levels mean that it is unsafe to interact with the river after a CSO event and you should have “no contact” with the river for at least 48 hours. This includes avoiding activities like swimming, wading, kayaking, and fishing.
What is currently being done to combat CSOs?
Combating CSO events is a huge and expensive challenge that will require large scale infrastructure changes. Communities are conducting infrastructure work, as well as exploring other solutions including building underground storage tanks to temporarily hold stormwater and expanding the capacity of wastewater treatment plants. Reconciling the CSO issue in the Merrimack River will take many years, and in the interim it is essential for citizens to be safe and aware when interacting with this beautiful but sometimes unsanitary natural resource.
Stay tuned next week for a new blog post on how you can help reduce CSO’s in our region.