Sanitary Sewer Overflow Notification - Oct. 29, 2024

October 30, 2024 - ​In the late morning of Oct. 29, 2024, city staff was notified of sewage and debris at a sanitary sewer manhole in a grassy area near a city-owned manhole behind the Ann Arbor Public Schools Bus Garage with evidence of the sewage reaching the nearby storm ditch.

City Public Works staff immediately investigated and found that the sanitary pipe was blocked with fats, oils and grease (collectively known as FOG). Staff quickly removed the blockage and resumed flow to the sanitary sewer system. An estimated 450 gallons of raw sewage was released to the grassy area, some of which ultimately flowed to the storm ditch, which flows and daylights to Malletts Creek. The affected grassy area was cleaned then lime applied to neutralize any potential contamination. Malletts Creek ultimately flows to the Huron River, at South Pond.

In accordance with regulatory protocols, City of Ann Arbor staff contacted the Michigan Department of Environment, Great Lakes and Energy (EGLE) to inform them of this incident.

Fats, oils, and grease are common household and industrial byproducts that are too often carelessly rinsed down the drain only to wreak havoc on sewers and sanitary collection systems. As evidenced by the incident yesterday, FOG can create blockages that lead to sanitary sewage overflows and other system backups - including on private property.

FOG in households and restaurants come from several everyday products used in food preparation, such as:

• Lard and meat fat byproducts

• Dairy-based products

• Typical cooking oils

• Butter and margarine

• General food waste

• Sauces
  

​Once these cooking byproducts are washed down the sink and enter the plumbing system, the compaction will get bigger and bigger until the pipeline has been completely blocked causing sewage to flow back up into homes, streets or backyards. Expensive cleanup crews will need to come out to resolve the issue, and/or the city will need to boost its maintenance processes, causing an increase in sewer utility bills.

Commercial areas (i.e., restaurants or multi-tenant housing like apartment buildings or dormitories), usually rely on the use of a grease trap or interceptor to catch much of their FOG. When maintained properly, these grease traps are effective at stopping a portion of FOG from entering the sewer system. But without regular maintenance, and an over-reliance on chemicals that claim to dissolve grease, FOG reaches the sanitary sewer pipes, and can lead to clogged pipes, causing backups and sewage overflows.

Home garbage disposals that connect to the plumbing system are unable to keep FOG out of the sewer collection system, too. These home units are made to shred solid food materials into smaller pieces. Commercially available "grease-dissolving" detergents simply move the FOG further down the collection system to cause further damage down the line. The city advises residents to be sure to scrape food from plates into the trash (or compost acceptable waste), and not simply dispose of them down the drain.

For further information, please visit https://www.a2gov.org/departments/public-works/Pages/Fats%2c-oil%2c-greases-and-wipes%2c-oh-my.aspx.

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