Minneapolis Department of Public Works

Public Works

350 South 5th Street
RM 203 City Hall
Minneapolis, MN  55415-1390

General Sewer Questions

What is a sanitary sewer system?

A sanitary sewer system is a collection of pipes, pumps and lift stations, manholes, service lines, and other infrastructure.  This system is designed to handle and safely transport used water, body wastes, and toilet paper as sewage to a treatment plant.

What is a sewer main line?

A sewer main line is a utility pipe that carries wastewater from the connected laterals to the wastewater treatment plant (via sewer force or gravity main).

What is a sewer lateral?

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

What is the difference between the storm drain system and the wastewater system?

The storm drainage systems consists of the natural and man-made channels and underground pipes (called storm drains) that carry rainwater and snowmelt from streets, yards and other areas. This water goes directly to our lakes, rivers and streams carrying pollutants with it. Stormwater entering the storm drain system is not treated, and flows directly into the Mississippi River, or lakes, streams, and stormwater holding ponds.

Wastewater entering the City's wastewater system flows directly to a treatment plant in Saint Paul called the Metropolitan Wastewater Treatment Plant, formerly known Pig's Eye Treatment Plant. The Metro Plant 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; stormwater is not transported to the Metro 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. The wastewater/sanitary system is composed of a network of pipes and manholes. It is used to collect and transport used water from sinks, washing machines, toilets, car washes and other facilities to the Metro Plant.

Read more about the City's efforts to eliminate Combined Sewer Overflows here: Combined Sewer Overflow - A Minneapolis Solution

What is a sanitary lift station?

Sanitary lift stations pump wastewater, also called sewage, in a sanitary sewer from a low point to a higher point downstream.  This enables the wastewater to flow by gravity to the next low point downstream.  Eventually this sewage discharges into large sewer pipes called interceptor sewers.  These interceptors are owned and maintained by MCES.

How does Minneapolis treat wastewater?

At the Metro Plant, sewage from the collection system first enters the preliminary treatment facility where large objects are screened out. The flow then enters settling tanks where solids are settled to the bottom of the tanks. This flow, consisting of dissolved and microscopic pollutants, then enters the secondary treatment process where it is mixed with microscopic organisms and air in aeration tanks. The microorganisms use the pollutants as a food source and breakdown the pollutants. The flow, including the microorganisms, then enters final settling tanks where they settle to the bottom of the tanks and return to the aeration tanks for reuse. The cleaned effluent is then; during the warmer months of the year, disinfected with a bleach product and chemicals and discharged to the Mississippi River, or discharged directly to the river during the cold months of the year.

Why can't I pipe 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 house should have a vapor trap, sometimes known as a "P" trap. This "U" shaped pipe is 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 the house through the sink drain.

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 home'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 are some of the problems that can occur?

When sewer gasses are present inside the home, usually a vapor trap has dried out. The water in a vapor trap will evaporate if the fixture is not used often; seldom-used bathrooms or utility sinks are commonly odor sources. The simple solution is to periodically run a small amount of water down the drain to refill the trap.

What can be done concerning rats in the City?

Rats unfortunately do live in the sanitary sewer system as it is impossible to eliminate them entirely.  The City can bait sanitary sewers with industrial strength poison as needed to help keep the rat population at a minimum.

If we suspect a rat infestation after observing suspected "rat holes", the City can also bait in and around private property.

Last updated Mar. 18, 2013