Private Property Infiltration & Inflow Reduction Program

The goal of the Private Property Infiltration and Inflow Reduction Program is to reduce the risk of basement backup events, by reducing the amount of clear water that enters the sanitary sewer system through private property infiltration and inflow points.

The program is being funded through a grant provided by the Milwaukee Metropolitan Sewerage District's (MMSD) Private Property Infiltration & Inflow Reduction Program. This is a 10-year program (2010-2020) and is considered a demonstration project to provide MMSD and the City with data to study the effectiveness of various infiltration and Inflow (I/I) reduction remedies such as sanitary building sewer (lateral) rehabilitation and foundation drain disconnections.

What is Infiltration & Inflow - I/I

Infiltration is groundwater that enters the sanitary sewer system through defects in sanitary sewer pipes. The defects in sanitary sewer building sewers (laterals) include cracks, open joints, root intrusion points, and faulty connections into the public sanitary sewer. These infiltration points give a pathway where clear water may enter the sanitary sewer system.

Inflow is the addition of clear water into the sanitary sewer system at points of direct connection to the sanitary sewer system. Some examples of inflow points are roof drain downspout connections, foundation drain connections, and storm drain cross connections that are connected into the sanitary sewer system, rather than the storm sewer system.

The water that enters the sanitary sewer system through infiltration and inflow points is called "clear water" (although it may be dirty) to distinguish it from normal sanitary sewage water in the sewer system.

The City of Milwaukee is served by two different sewer systems. The first is the combined sewer system, where sanitary sewage and stormwater are conveyed through a single pipe. The second is the separated sewer system, where sanitary sewage and stormwater are conveyed separately in two pipes. The sanitary sewer in a separated sewer system is designed to carry base sanitary flow only, so the increase in flow due to I/I in a separated system can cause the sanitary sewers to surcharge, which increases the risk of basement sanitary backups. Furthermore, the excess water that enters the sanitary sewer system due to I/I is conveyed to the wastewater treatment plants, where it must be processed. The water added to the system due to I/I negatively impact the performance and efficiency of the wastewater treatment plant and increase pumping and treatment costs, energy consumption, and maintenance requirements. These negative impacts result in higher wastewater treatment costs, which are therefore transferred to the users through increases in user charges.

Sanitary Sewer Lateral Rehabilitation Project

The sanitary sewer pipe that connects a home to the public sanitary sewer in the street is called the sanitary sewer lateral. Laterals may have defects such as cracks, open joints, root intrusion points, and faulty connections into the sanitary sewer main or manholes, which allow for infiltration to enter into the sanitary sewer system. This portion of the program removes the sources of infiltration caused by faulty laterals by rehabilitating a home's lateral.

The rehabilitation starts with an inspection of the lateral, and is completed using trenchless cured-in-place pipe (CIPP) technology. CIPP is a method of sewer rehabilitation that involves a flexible liner that is inserted inside the existing pipe. This liner is inflated inside the pipe, and then cures to a hard state. The final product is a seamless, jointless, structural pipe.

Homes may also have a storm water lateral that collects rain water from their home’s roof and foundation drains. The storm lateral is connected to the public storm sewer in the street, and is conveyed to a waterway, rather than the sewage treatment facility.

Before:                                                                      After:
Lateral has various defects. Groundwater                        Lateral is smooth and sealed. Groundwater cannot  
can enter the lateral through Infiltration points.             enter the lateral.

Foundation Drain Disconnection Project

Most homes built after 1920 have foundation drains that surround the home. These drains collect the ground water that gathers at the home's foundation, and drains the water away from the home. Many homes in the City of Milwaukee that were built prior to 1954, had their foundation drains directly connected into the sanitary sewer system, rather than being collected by sump pump system and discharged into a storm sewer or into the home's yard. Foundation drain connections contribute a considerable amount of inflow into the sanitary sewer system. This portion of the program removes that source of inflow by disconnecting foundation drains from the sanitary sewer system, and rerouting the drains into a newly installed sump pump system.

More information on the Private Property Infiltration and Inflow Reduction Program

For more information on this project, please download the informational slideshow presentation below:
Private Property Infiltration & Inflow Reduction Program

For more information on your home plumbing layout, download the PDF below:
Typical City of Milwaukee Home Plumbing Layout

Additionally, please visit the MMSD website linked below. There, you can watch videos explaining the work further, and learn more about how this project can help to reduce the risk of basement backups in your neighborhood. 
https://www.mmsd.com/what-you-can-do/keep-your-basement-dry.