New Haven, CT
Home MenuCombined Sewer Overflows (CSOs)
On this page, you can find information on Combined Sewer Overflows and an automatically updated report on CSOs that have occurred in the last two weeks. If you'd like to see the report on CSOs in the last two weeks, please click this link to jump to that section.
What are Combined Sewer Overflows (CSOs)?
Sanitary sewers are pipes which carry wastewater from homes and businesses (i.e. wastewater from toilets, laundry, bathing, dishwashing). Storm sewers are pipes that carry rainwater from storms. A pipe which is designed to carry both types of flow is called a combined sewer.
While most communities have separate systems for sewage and stormwater management, some Connecticut cities have combined sewer systems that were designed over a 100 years ago and still collect and convey both sewage and stormwater in one pipe. This system allows municipalities to treat both stormwater and wastewater at once to meet water quality standards prior to discharge into a water body.
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The problem with combined sewer systems is that heavy rains can overload them, causing them to discharge untreated sewage into Connecticut’s waterbodies at points known as combined sewer overflows (CSOs). CSOs are primarily a health risk to people swimming, fishing, or consuming shellfish harvested in the area around the CSO, as bacteria and viruses in the untreated sewage contaminate the water. As a result of climate change, the intensity of rainfall is increasing and causing more severe weather events, leading to more discharges from the state’s combined sewer systems.
How long does water stay impacted after a rain event?
After rain stops, it can take up to 48 hours (2 days) for the water near the CSO to return to baseline conditions. During this time, the bacteria die off and the currents dilute the germs and chemicals in the water. It is important to note: CSOs can and do occur with less intense precipitation events. The type of precipitation event that triggers a CSO(s) is very specific and dependent on the duration and intensity of an event, the level of saturation of ground conditions during the event, and the capacity and structural condition of a specific pipe or segment of a municipality’s combined sewer system.
How can the public know if combined sewer overflow discharges of raw sewage have occurred?
The City of New Haven has worked with Connecticut’s Department of Energy and Environmental Protection to provide an automatically updated report of CSOs that have occurred in last two weeks.
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What are the health risks of CSOs?
The Connecticut Department of Energy and Environmental Protection (CT DEEP) advises residents from recreating in waters known to receive CSOs in the past 48 hours.. View a statewide map from CT DEEP showing locations of the CSOs.
If you do go in the water near a CSO location during or after a heavy rain, the greatest health risk would come from getting untreated overflow water in your mouth. If you accidentally go in the water near a CSO location during or after heavy rain, avoid getting water in your mouth and wash yourself with hot water and soap as soon as possible. Most people will not get sick by just getting untreated overflow water on their skin.
There is a chance that pathogens (bacteria and viruses) in untreated overflow water could make you sick, especially if you are already sick or have lower immunity. In general, young children and elderly people may have a higher risk of getting sick from untreated overflow water.
Content from CT DEEP CSO FAQ page and City website.