Inflow & Infiltration (I/I) Program

Storm water creates problems in the sanitary sewers

What is inflow/infiltration?

Inflow and infiltration (I/I) is clear water that enters the sewer system from a variety of sources.

  • Infiltration occurs when groundwater seeps into sewer pipes through cracks, leaky pipe joints and/or deteriorated manholes.
  • Inflow is storm water that enters the wastewater system through rain leaders, basement sump pumps or foundation drains illegally connected directly to a sanitary sewer pipe.


Why is I/I a problem?

I/I is a problem because it takes up fixed capacity in large regional sewer pipes (interceptors), capacity that will be needed for future households in the region. I/I can also be costly to communities. Once clear water gets mixed in with wastewater, communities are charged for the treatment of all the water. 

Building additional interceptor and treatment capacity to handle excessive I/I is not financially prudent; it is much cheaper to eliminate I/I at the source. Metropolitan Council Environmental Services (MCES) and communities in the seven-county region are working hard to reduce I/I in the regional wastewater system in order to preserve capacity as well as protect public health and the environment.

What is the Inflow/Infiltration Surcharge Program?

The original program was recommended by the Council's I/I Task Force in 2004 and approved by the Council. The task force included representatives serving at large from 15 cities across the region and from Metro Cities. The program provided financial incentives for cities to reduce excessive I/I into the regional wastewater system from both public and private sources.

Rationale for and methodology of the surcharge

In 2009, the Council established a Demand Charge Task Force to develop recommendations to update the program. Instead of Demand Charges, the Task Force recommended (and Council approved), an "Ongoing Surcharge Program." Exceedances under this new program are now being measured (for surcharges in 2013).

I/I 2013 Clean Water Fund Grant Program

The 2013 Minnesota Legislature, through Clean Water Fund appropriations, approved a total of $1,000,000 in grants or loans for local infiltration and inflow reduction programs.  This grant funding will be used to address high priority areas in the metropolitan area.  More about the 2013 I/I reduction program.

Clean Water Funds Appropriated
Amount Encumbered $1,000,000.00
Available as of July 16, 2014


I/I Municipal Grant Program

In 2012, the State Legislature approved a $4 million grant program bonding bill for the purpose of providing grants to municipalities for capital improvements to public infrastructure to reduce I/I.  
The Metropolitan Council Environmental Services manages the Grant Program.

2014 Municipal Grant Requirements and Grant Design Guidelines


In 2014, the State Legislature approved another $2 million of funding for the purpose of providing grants to municipalities for capital improvements to public infrastructure to reduce I&I. As before, the Metropolitan Council Environmental Services will manage the program. Program design and guidelines are in process review and development. To review a tentative program design and schedule, please see the attached presentation (pdf).

Inflow/Infiltration tool box

Highlights possible programs and products as solutions for communities to reduce I/I. Includes:

Getting Started
Investigative Techniques
Corrective Actions--Private Property
Corrective Actions--Publicly Owned Sewers
Sample Specifications
Sample Ordinances

A list of links, web sites, references, and resources to provide additional information about this national problem. 

Contact information/billing

Bills/charges/fees to residents are not sent by the Met Council; resident bills are coordinated by the individual resident's city.

  • Property owners should contact their local government unit about charges, fees and other questions.
  • Municipal staff should contact: 651.602.1020 for financial information or 651.602.1517 for technical information.