Inflow and Infiltration

I and I culprits

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What is I/I?
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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.

Because the sanitary sewer system was not designed to handle this excess clear water, it becomes overloaded during times of high groundwater or heavy rainfall. This can cause basement flooding or bypassing of raw wastewater to local streams and lakes.

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), which provides regional wastewater collection and treatment for the metropolitan area, 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.

Golden Valley was identified as a contributor of excess I/I and is working to resolve the problem.

I/I Inspections Program

To comply with MCES directives regarding I/I, the City inspects homes and businesses in Golden Valley to determine if roof drains, foundation drains, sump pumps, and other clear water sources are connected to the sanitary sewer system. The goal of this program is to reduce excessive flows that enter the sanitary sewer system so the City, and its utility customers, won't have to pay MCES surcharges.

Who is subject to an inspection?

  • All properties in Golden Valley must be inspected and required to be in compliance before they can be sold. Please call the City at 763-593-8030 to verify that your property is in need of certification before beginning the I/I certification process.
  • Property owners who apply for plumbing permits, variances, subdivisions, or other actions from the City will also be subject to an inspection.
  • The City will conduct I/I inspections as part of its annual Pavement Management Program (PMP) the year prior to the street reconstruction.


For properties that pass inspection, the City issues a Certificate of I/I Compliance to the property owner and keeps a copy on file at City Hall. Properties that don’t pass inspection are issued a correction notice delineating the problems. Repairs should be completed within 180 days of the first inspection, and the City can grant an extension of another 180 days. If repairs are not completed within one year of the first inspection, the inspection becomes invalid and the process starts again, which includes paying the applicable inspection fee. The City issues a Certificate of I/I Compliance upon a successful re-inspection.

I/I Problem Spots

The inspection involves televising the sanitary sewer service out ot the City sewer main (to identify cracks and leaks) and checking the sump pump discharge system and roof drains and leaders (to identify improper connections to the sanitary sewer system).

  • Roof Drains/Leader
  • Foundation Drains
  • Sump Pump Systems
  • Sanitary Sewer System

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.

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 or be connected to the City's storm sewer system.

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).

Wastewater from Golden Valley 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.


I/I Questions and Answers

+Why is Golden Valley a leader in this program?

Although Golden Valley has led the Twin Cities metro area in reducing I/I, we are not the leader in Minnesota. Other cities (Duluth, Waseca, Glencoe, Hamburg, Tower) have been working for years to reduce I/I and continue to complete private property inspections as part of the effort. Once Golden Valley’s City Council and staff understood the environmental, sanitation, and financial impacts of I/I, they committed to a proactive approach to reduce it. To track progress, staff monitors sewer flow at nine sites throughout the city and groundwater levels at seven sites. However, dry weather conditions in recent years make it difficult to document the true effects of I/I related improvements.

+When is Golden Valley's inspection required?

Golden Valley's inspection is required before a home can be advertised for sale. Repairs should be completed, and a certificate of compliance issued, before the closing. If repairs cannot be made before a title transfer, then escrow is required. The certificate of compliance stays with the property after the sale.

+Why does the City require inspections only for homes that are for sale?

After studying other programs, City officials concluded the cost of such a repair might be easier on homeowners at the time of a sale, when they typically have access to funding from home equity.

+If I have the inspection and decide not to sell, do I still need to complete the repairs?

Repairs should be completed within 180 days of the first inspection, and the City can grant an extension of another 180 days. If repairs are not completed within one year of the first inspection, the inspection becomes invalid and the process starts again, which includes paying the applicable inspection fee.

+Can the buyers assume responsibility for the repairs?

Yes, if arrangements are made for escrow with the closing agent and an I/I Compliance Agreement is signed by the City and the responsible party. The seller is responsible for the initial inspection.

+How is MCES regulating I/I compliance?

While some cities have been successful at reducing I/I, the regional problem is still significant and more participation is necessary. To enforce this, starting in 2013 MCES will implement a wastewater demand charge for communities with excessive I/I, including those with reduction programs. This means a city could get assessed a surcharge if it were to exceed sanitary sewer flow levels during a major rain storm, even if it had previously shown reduced flow rates through I/I mitigation.