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Sewer and Storm Drain Unit
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General Sewer Questions

What is a sanitary sewer system?

A sanitary sewer system is a collection of pipes, pumps, lift stations, manholes, sanitary sewer laterals and other infrastructure. The system is designed to safely transport wastewater to a treatment plant.

What is a sewer main line?

A sewer main line is a pipe that carries wastewater from a property's sanitary sewer lateral to a treatment plant, via sewer force or gravity main.

What is a sanitary sewer lateral?

A sanitary sewer lateral is a pipe that carries wastewater from your property to a sanitary sewer pipe in the street. Every property receiving sewer service from the City of Minneapolis has at least one sanitary lateral.

What is the difference between a storm drain system and a sanitary system?

A storm drain systems consists of natural and man-made channels and underground pipes (called storm drains) that transport stormwater and snowmelt from streets, yards and other areas and discharges directly into our lakes, rivers, creeks and stormwater holding ponds. This stormwater is not treated, and it picks up and carries pollutants along with the stormwater, before discharging into the storm drain system.

Wastewater entering the Minneapolis sanitary system is transported to the Metropolitan Wastewater Treatment Plant in Saint Paul. This facility is owned and operated by Metropolitan Council Environmental Services (MCES).

What is the difference between a separate sanitary sewer system and a combined sewer system?

A separate sanitary sewer system is designed to carry only wastewater to a treatment plant. Stormwater is carried in a separate stormwater system, and is not transported to a treatment plant. In a combined sewer system, both wastewater and stormwater are carried in the same pipe. The City of Minneapolis has very few combined sewer systems.

Read more about the City's efforts to eliminate Combined Sewer Overflows.

What is a sanitary lift station?

Sanitary lift stations pump wastewater in a sanitary sewer from a low point to a higher point downstream, allowing the wastewater to flow downstream. This wastewater eventually discharges into large interceptor sewer pipes, which are owned and maintained by MCES.

How does Minneapolis treat wastewater?

At the Metropolitan Plant, the wastewater discharges into a preliminary treatment area that screens out large objects, before entering settling tanks where solids settle to the bottom.

The flow containing pollutants then travels to a secondary treatment process, mixing with air and microorganisms in aeration tanks. These microorganisms use the pollutants as a food source, breaking them down. Lastly, the flow enters final settling tanks, falling to the bottom before returning to the aeration tanks for reuse.

During warmer months, the cleaned effluent is disinfected with a bleach product and chemicals, before being discharged to the Mississippi River. During colder months, the cleaned effluent is discharged directly to the river. 

Why can I not discharge stormwater from my sump pump into my sanitary drain?

MCES does not allow stormwater to be discharged into the sanitary system. Stormwater does not need to be treated.  

What is the purpose of vapor traps?

Every water fixture in your property should have a vapor trap, also known as a "P" trap. This "U" shaped pipe should be visible under sinks, and is present in some form on all lines draining to the sewage system. The "U" shape of the pipe holds water, preventing gases from backing up from the sewer into your property.

What is the purpose of the roof vent?

All houses have plumbing vents (also called a vent stack) that extend through the roof. These vents allow air to flow in and out of your property's plumbing system, helping water to flow through the pipes. Working in combination with the vapor traps, gases from the sewer system are safely vented.

What problems can occur?

When sewer gasses are present inside a building, a common problem is the vapor trap has dried out. The water in the trap evaporates if the fixture is not used often; seldom-used bathrooms or utility sinks are common odor sources. The simple solution is to periodically run water down the drain to refill the trap.

Are there rats in the sanitary sewers of Minneapolis?

Rats do live in sanitary sewer systems; it is impossible to eliminate them entirely. The City can bait sanitary sewers with industrial strength poison as needed to help control the rat population.

Last updated Feb 23, 2018



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