Inflow and Infiltration (I/I) Program

Mitigate the excessive clear water entering the wastewater collection systems

Since 2005, efforts by communities, property owners, and MCES have helped to reduce the regional annual wastewater volume by roughly nine billion gallons. The flow decrease has occurred even as precipitation volumes, rainfall intensities, and population have increased.

Inflow and Infiltration – or I/I – are terms that describe clear water that enters wastewater collection systems and consumes capacity of the conveyance and treatment systems. Excessive flows can result in public and environmental health concerns if untreated sewage discharges to basements, rivers, or lakes.

Each has unique sources, methods of entry, and effects on the wastewater collection system. Both are costly to communities and utility ratepayers due to increased conveyance and treatment costs.


Inflow is typically stormwater that increases peak flow in the wastewater system during and after rainfall events from point sources such as broken manhole covers, sewer cleanouts, sump pumps, foundation drains, and rain leaders.

Infiltration is typically groundwater that gradually enters the wastewater system through cracks and openings in sewer mains, service laterals, joints, and deteriorated manholes. Infiltration increases base flow in the wastewater system and removes water from the natural hydrologic cycle, which could otherwise recharge the regional aquifers.

Why the region needs to reduce I/I

Some of the major challenges in the region associated with excessive flows attributable to public and private I/I include:

  • Public and environmental health concerns. When the combined amount of wastewater and clear water exceed the system capacity, untreated wastewater can back up into the basement of buildings or discharge into lakes, streams, wetlands or other areas
  • I/I is costly to communities and utility ratepayers. The large regional pipes (interceptors) and wastewater treatment plants are designed for the needs of a growing region. Excessive I/I takes up capacity in the wastewater collection and treatment system intended to accommodate regional growth and increases wastewater treatment costs charged to communities.
  • I/I wastes the region’s valuable water resource. Clear water discharged to the wastewater system is removed from the natural hydrologic cycle and reduces groundwater recharge potential.

Private property I/I mitigation in the region

Upstream of the regional and local systems, there is an estimated 7,500 miles of private service laterals connected to roughly one million private properties. Just like public infrastructure, private service laterals can be sources of infiltration and may require repair or replacement.

Sumps pumps and drains are also sources of inflow. Based on information from the Water Environment Foundation, one sump pump can add up to 7,200 gallons per day of clear water into the wastewater collection system – equivalent to 40 homes worth of typical wastewater use.

Grant funding of I/I mitigation

In recent years, the State Legislature has approved bonding bills for the purpose of providing grants to municipalities for capital improvements to public infrastructure to reduce I/I. Information on current programs is below; see information about MCES funding and grant programs.

2017 Municipal I/I Grant Program

The State Legislature has approved $3.739M of funding for the purpose of providing grants to municipalities for capital improvements to public infrastructure to reduce I/I. Metropolitan Council Environmental Services (MCES) manages the program and presented an information session on July 18 at the League of Minnesota Cities/Metro Cities Office Building.

MCES Ongoing Inflow/Infiltration Program

The Met Council program provides financial incentives for communities to reduce excessive I/I into the regional wastewater system from both public and private sources. The program began in 2004 as a recommendation from a task force, which included representatives serving communities across the region. Since that time, 49 communities have participated in the program and have invested a combined total of $157 million into the local infrastructure.

The Task Force has recommended revisions to the program, included those included in the 2016 I/I Task Force Report. The Council accepted the report in November 2016 and authorized staff to implement the report’s recommendations, which fall into three categories:

  • Technical Assistance. Develop best practices and a model ordinance for inspection and repair programs, investigate the potential for cost-saving master contracts, and implement an I/I mitigation demonstration project.
  • Public Outreach. Develop a program for property owners and local officials that Includes topics such as impacts of excessive I/I during wet weather events and the proper maintenance of service laterals and sewers.
  • Financial Assistance. Support efforts to secure funding for public and private I/I mitigation projects from state and regional resources.

See the full 2016 I/I Task Force Report.

Inflow and Infiltration Toolbox

The Tool Box Manual (pdf) highlights possible programs and products as solutions for communities to reduce I/I.

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

Included are Tool Box References, which provides a list of links, web sites, references, and resources to provide additional information.

More information

Property owners should contact their local government unit about wastewater charges, fees and other questions. Bills/charges/fees to residents are not sent by the Met Council; resident bills are coordinated by the individual resident's community.

Questions or comments should be sent to

For municipal staff:

  • For program information, contact Marcus Bush at 651.602.1166.
  • For grant information, contact Matthew Gsellmeier at 651.602.1802.

Ongoing Inflow and Infiltration Program Procedure Manual (pdf)

Local Planning Handbook PlanIt Tutorial