A sanitary sewer overflow (SSO) is an unintentional discharge, spill or release of untreated sewage into the environment or a property. SSOs are also known as sewer backups and the resulting flooding can cause damage to a property and pollute the environment. Raw sewage is dangerous because it contains bacteria and other hazardous microorganisms. Touching or walking through contaminated areas can bring germs into uncontaminated areas of your home. Children and pets are especially vulnerable.
Causes of SSOs or Sewer Backups
- A blocked or collapsed private sewer lateral
- Improper disposal of grease that creates blockages in sewer lines or internal plumbing
- Obstructions or breaks in the sewer lines or in internal plumbing
- Improper disposal of other items, such as baby wipes or rags, that blocks sewer lines or internal plumbing
- Unusually heavy rainfall, which can result in an inflow of stormwater into sewer lines
Effects of SSOs & SSO Map
SSOs can cause significant environmental and public health problems. SSOs that occur in streets can cause sewage to enter the storm drain system and travel to local waterways. This can pollute surface waters, endanger aquatic life, and interfere with the recreational uses of waterways and beaches. SSOs that occur within buildings can damage the property and its contents, which can result in financial costs for the property owner, and pose a significant health risk to residents of the property, especially children and pets.
State and federal regulations now require BWSC and other sewer agencies to report SSOs in order to meet Clean Water Act requirements and to reduce the occurrence of SSOs across the BWSC system.
BWSC closely monitors sanitary sewer overflows that occur in Boston and maintains a Sanitary Sewer Overflows Map on the Maps page. The map and list identify recent SSO locations.
Keep Drains and Sewers Clear of Fats, Oils and Grease (FOG)
Fats, oils, and grease (FOG) can cause blockages in sewer pipes and lead to SSOs. Grease should never be poured down sink drains or into toilets or garbage disposals. Instead, pour grease and oil into a covered disposable container and put it in the trash. “COOL IT – CAN IT – TRASH IT.” Food scraps, meat fats, dairy products, and butter and margarine should never be put down the drain or into a garbage disposal.
Keep Wipes Out of Pipes
There are many disposable wipes that claim to be “flushable” and “sewer safe.” However, these wipes do not break down as they travel through pipes and into the sewer system. Wipes can create clogs in both household plumbing and the public sewer system and result in SSOs.
Wipes that should be disposed of in the trash, and not flushed down the toilet, include:
- Bathroom wipes
- Baby wipes
- Disinfecting wipes
Properly Install Backwater Valves
Heavy rainstorms can cause overland flooding and sewage backups into properties in low-lying areas. While overland flooding cannot always be prevented, sewage backups can be avoided if your property is properly equipped with a backwater valve.
A backwater valve is a fixture that is installed on a sewer line or drain in the basement. A properly installed backwater valve prevents the reverse flow of water, keeping sewage from entering your property.
For more information see our Backwater Valve Regulations brochure.
Maintain and Repair Sewer Laterals
A sewer lateral, also known as a building’s sewer, is the waste disposal pipe connecting a property to the BWSC sewer main in the street. BWSC is responsible for maintaining its sewer main located in the public way. Property owners are responsible for maintenance and repair of their building’s entire lateral from inside the property’s basement to BWSC’s sewer main in the street. Blocked and collapsed sewer laterals can lead to sewer backups into a property. Have your sewer lateral inspected for blockages, breaks, and leaks. If a problem is detected, repairing, replacing, or relining your sewer lateral can help prevent sewer backups.
The BWSC Sewer Lateral Financial Assistance Program is a financial reimbursement program that is designed to assist property owners with the cost of repair or replacement of their sewer laterals.
For more information see our Sewer Lateral Financial Assistance Program.
Sewer Lateral Financial Assistance Program
Disconnect your Downspout
Downspouts – also known as roof leaders – are familiar attachments on most buildings. Downspouts carry excess stormwater – including rain and snowmelt – off roof surfaces and out of gutters. Ideally this runoff goes into yards or other landscaped areas and is absorbed into the ground.
In the past some downspouts were directly connected to the sanitary sewer system, a practice that is now illegal. Any such illegal connections remaining in the City of Boston are potentially unhealthy for residents, harmful to the environment, and costly to all Boston Water and Sewer (BWSC) ratepayers.
The sanitary sewer system is meant to transport only the wastewater from our toilets, sinks, showers, washing machines and dishwashers. Sanitary waste is carried to MWRA’s Deer Island plant for treatment, and BWSC pays for this service based on volume. The addition of stormwater – which doesn’t require treatment – to the wastewater flow increases BWSC’s operating costs, costs which must be passed on to and shared by all ratepayers.
The cost factor aside, heavy amounts of stormwater in sanitary sewers can overburden the system, causing overflows that can inundate neighborhoods and homes with untreated sewage. In the case of combined sanitary/storm sewers, volume exceeding capacity may need to be discharged into local waterways, polluting our harbor and rivers with dangerous pathogens.
If you know or become aware that a downspout on your property is illegally connected to the sanitary sewer, you are urged to disconnect it immediately. You can DIY, or call your plumbing contractor. If you need further advice or have any questions about downspouts, call Boston Water and Sewer Commission at 617-989-7441. (Based on the property address alone, BWSC may be able to tell you if you have an illegal connection.)
Properly Install Sump Pumps
Install sump pumps to help keep your home dry by pumping ground water away from your foundation. Sump pumps must drain to your lawn or other yard area. It is illegal to have the sump pump connected to the sewer system. Such connections allow a tremendous amount of water to enter the system which, causes the sanitary sewer to exceed the pipe's capacity during wet weather and sewage can overflow into nearby ditches and streams or back up into downstream homes.
How to Report SSOs
To report a sanitary sewer overflow (SSO) or sewer backup, call BWSC’s 24-Hour Emergency Line at 617-989-7000.
If you experience a SSO:
- Avoid contact with sanitary flow
- Report any SSO to BWSC
- Use caution while cleaning following a backup or contact a cleaning contractor
See Cleanup Procedures after a Sewer Backup for more information.
Sewer Backup Cleanup Procedures