How It Works
The plumbing system inside your home or any building consists of a network of pipes, vents and traps. Each plumbing fixture (toilet, sink, shower, floor drain, etc.) is connected to the pipes that carry the wastewater to the public sewer.
Each plumbing fixture also has a vent that allows odors and sewer gases to escape and atmospheric pressure to enter, thus preventing 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. You can pour water down the drain to 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 line from the building to the public sewer (also called the sanitary service) needs to be cleared of clogs or obstructions such as tree roots. You can avoid clogs by preventing grease, hair, washing machine lint, disposable diapers, and other such items 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, you should first call Sewer Maintenance to make sure it was not caused by a problem in the public sewer. Checking the public sewer is a free service provided by the City. If the problem is not with the public sewer, you should then call a professional contractor to resolve the issue. Backwater valves may reduce the likelihood of sewer backups.
Minneapolis Sewer System
Sanitary sewer mains typically run down the middle of the street. Vertical openings (called manholes) allow access for maintenance. Manholes run from 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) that take it to the Metropolitan Wastewater Treatment Plant in St. Paul.
Sewers usually flow downhill, using gravity to move the wastewater along. Sewer mains often follow streams, which also flow downhill. The main tunnel from Minneapolis to the MCES Metro Plant follows the Mississippi River. When gravity doesn't work, pump stations force the wastewater to a higher level, where gravity is able to take over again.
When the wastewater reaches Metro Plant, several steps are taken to treat the discharge. First, wastewater passes through a large iron grate to separate large items. After that, the solids are settled out, collected and incinerated. Next, bacteria is 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 waters of the state.
Stormwater runoff in Minneapolis flows into storm drains through catch basins (storm drain inlets) located in city streets. The collected stormwater then runs through a series of tunnels that eventually empty into the Mississippi River. The catch basins are critical to controlling runoff. They should not be clogged, and nothing but stormwater should be drained into them. In some areas you will see Catch Basin Stenciling (web page coming soon!) with the words Please Don’t Pollute! Drains to River (Creek or Lake).
Property owners are encouraged to drain stormwater to lawns, gardens or small ponds. Special Rain Gardens can be established to catch extra water. Rain Barrels can also be used to catch the water 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, and streets into ditches, culverts, catch basins, and storm drains. Examples of pollutants that hard surfaces collect are:
- Vehicle oil and grease
- Construction sites 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. To assist preventing these pollutants from reaching streams and lakes, the City has built 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. 19, 2012