Inflow and Infiltration (I&I)

Sanitary Sewer System
Wastewater from Roseville travels through the City’s sanitary sewer system to the Metropolitan Wastewater Treatment Plant, which is operated by the Metropolitan Council Environmental Services Division (MCES).  MCES treats wastewater for communities in the seven county metropolitan area.

Inflow and Infiltration (I/I) is the excess flow of clear water into the City's sanitary sewer system.

Inflow is when clear water from illegal connections of sump pumps, downspouts, and foundation drains is channeled directly into sanitary sewer pipes.

Infiltration is when groundwater seeps into sewer pipes via cracks or leaky joints.

Click on the link to see a figure showing the various ways I/I gets into the sanitary sewer system.

What's the problem?
The excess clear water from I/I problems uses sanitary sewer capacity needed for wastewater.  The result is sewer backups and increased costs (about $300-$400 million annually) for needlessly putting clear water through the wastewater treatment process.

The Metropolitan Council Environmental Services (MCES) requires communities with excess I/I to invest in local reduction remedies such as disconnecting sump pumps and foundation drains from sanitary sewers and repairing leaky sanitary sewer pipes. Such actions will cost roughly $150 million, instead of the nearly $1 billion it would cost to build additional sewer infrastructure to provide capacity during big rain storms.  To urge compliance, MCES incorporated surcharges for communities with excess I/I.  Roseville, along with 74 other cities, was identified as a contributor of excess I/I and is working to resolve the problem.

Click on the link to view a video that shows how private property owners can address I/I on their properties.

Did you know improperly connected sump pumps and drainage systems are creating a big problem?

“Clear Water” is going to the wrong place.

The problem can come from many different places.  In our homes and businesses, rainwater can be directed into the sanitary system by an improperly connected sump pump, an improper foundation drain or roof gutter connections directly to the sanitary sewer line.  When “clear water”, such as rainwater, ground water or snowmelt, enters the wastewater treatment system, it is known as inflow.

Sump Pump Inspection Program
Roseville City Code, Section 802.08, states that discharge into the City’s sanitary sewer system shall be in conformance with the Metropolitan Council Environmental Services Waste Discharge Rules. Unpolluted water, such as rain water, storm water, groundwater, and water collected from foundation drains, is not permitted to be discharged into the sanitary sewer system.

To comply with MCES directives regarding I/I, the City of Roseville is implementing a sump pump inspection program in conjunction with the water meter replacement program. Completing sump pump inspections in residential homes will provide staff preliminary information on how many non-conforming connections there are, and whether this is a major contributing factor to the City’s I/I problem.  Staff will use the collected data to develop further I/I reduction plans in the City for recommendation to the City Council. 

Sump Pump Systems
Sump pumps are designed to capture surface or ground water that enters basements or crawl spaces and pump it away from the house.  The basic sump system includes drain tile, a sump pit, a sump pump, a float or switch, and a drain line.  The sump pit extends below the slab and collects surface water that enters the basement/crawl space or groundwater that rises to the slab.  Sump pumps should not be connected to the sanitary sewer.  Sump pumps should drain into the City’s storm sewer system through one of two methods: a direct connection (a pipe from the house to the main storm sewer line), if available, or directly onto the ground (preferably 20 feet from the house and not into a neighbor’s yard).

Foundation Drains
Foundation drains are underground pipes that collect storm water from around the base of a building and into a sump basket, where it is then pumped outside of the building.  Foundation drains should not be connected to the sanitary sewer.  If your foundation drain system is connected to the sanitary sewer, correcting the problem could be costly.  The process could involve excavation to disconnect the foundation drain from the sanitary sewer and installation of a sump pump system.  The new sump system must pump directly to the ground outside of the building.

Roof Drains/Leaders

Roof drains and leaders direct storm water from roof gutters to the ground through pipes and downspouts.  Roof drains should not be connected to the sanitary sewer but should discharge to the ground outside of a building.  If your roof drains are connected to the sanitary sewer, disconnect them, plug any open connections to the sanitary sewer using a non-shrink permanent material, and redirect the roof drains onto the ground outside the building.

For more information, click on the link:  Met Council Inflow and Infiltration Program

Please contact Public Works at or 651-792-7004 if you have questions or would like more information on I/I.