How It Works
Your building's plumbing system consists of a network of pipes, vents and traps. Each plumbing fixture (toilet, sink, shower or floor drain) is connected to the pipes that carry the wastewater via your sanitary service (or lateral) to the public sewer.
These fixtures have a vent that allows odors and sewer gases to escape and atmospheric pressure to enter. This prevents backpressure when water fills the pipes. The trap in each fixture, when properly vented, provides a liquid seal that prevents sewer gases from entering the building. If a fixture is not used regularly, water in the trap may evaporate. This can cause the loss of the trap seal and allow sewer gases to enter the building. Pouring water down the drain will replenish the trap seal. Remember that sewer gases can be fatal.
A readily accessible cleanout is required near the outside wall where the building drain connects with the sewer. This cleanout (usually located near the vent stack) is used when the sanitary service/lateral from the building to the public sewer needs to be cleared of obstructions such as tree roots. You can avoid these obstructions by preventing grease, hair, washing machine lint and disposable diapers from entering the drainage system. The cost for cleaning the sanitary service is the responsibility of the building owner.
If you experience a sewer backup, contact Sewer Maintenance to ensure the problem was not caused by a public sewer. There is no fee to request a check in a public sewer. If we determine the problem is not in the public sewer, you should call a professional contractor to assess the issue. Backwater valves may reduce the likelihood of sewer backups.
Minneapolis Sewer System
Sanitary sewer mains typically run down the middle of a street. Vertical openings (called manholes) allow access for maintenance. Manholes are built on top of the sewer main, up to street level, where they are covered by manhole covers. The sanitary sewer main opens into progressively larger pipes, until the wastewater reaches the large tunnels (also called interceptors), before being transported to the Metropolitan Wastewater Treatment Plant in St. Paul.
Sewers usually flow downhill, using gravity to transport the wastewater. Sewer mains often follow streams, which also flow downhill. The main tunnel from Minneapolis to the Metropolitan Wastewater Treatment Plant follows the Mississippi River. When gravity doesn't work, pump stations force the wastewater to a higher elevation, where gravity is able to take over again.
When the wastewater reaches Metropolitan Wastewater Treatment Plant, the following steps are taken:
- Wastewater passes through a large iron grate to separate large items.
- Solids are then settled out, collected and then incinerated.
- Bacteria is then used to remove organic materials and nutrients, after which the bacteria is settled out.
- Finally, phosphorus and nitrogen are removed, and chlorine is added. The water is finally ready to be released to the Mississippi River.
Stormwater runoff flows into grated covers on top of storm drain inlets, which are located in the street. This stormwater flows through storm drain pipes before discharging into the Mississippi River. The storm drain inlets are critical to controlling runoff. They should be kept free of debris and nothing but stormwater should empty into them. Some storm drains in Minneapolis have messages like DO NOT DUMP - DRAINS TO RIVER on them. See Storm Drain Stenciling for more information about the program.
Property owners are encouraged to drain stormwater from their property to lawns, gardens or small ponds. Rain Gardens can be installed capture this stormwater, allowing deep rooted native plants and soil to naturally filter out pollutants & contaminants from the stormwater. Rain Barrels can also be used to capture stormwater from roofs. This water can then be used to water lawns and flower gardens.
Stormwater runoff flows off hard surfaces such as roofs, driveways, parking lots, collecting pollutants along the way. Some examples of this include:
- Vehicle oil & grease
- Construction site sediment
- Bacteria from animal waste
- Excess lawn fertilizer and pesticides
- Airborne pollutants, such as nitrogen, mercury, other metals, combustion emissions and pesticides
A typical downtown city block produces about nine times more runoff than a wooded area of the same size! Rainwater washes the hard surfaces, and the first runoff carries these pollutants directly to nearby streams and lakes, by way of the storm drain system. To assist preventing these pollutants from reaching our water bodies, the City builds holding ponds and grit chambers that allow the pollutants to settle out, as well as establishing wetlands to further filter out these pollutants.
Last updated Jan 25, 2017