March 2009 View a presentation describing the City of Duluth's Inflow & Infiltration reduction project.
For more information about
the City of Duluth’s I&I program please
Read about steps taken by the Western Lake Superior Sanitary
District (WLSSD) to control
the problem (2.5 MB pdf).
Visit the WLSSD
website for their latest news releases.
I&I: Inflow & Infiltration
What is I & I?
This term describes one of the main causes of sewer overflows around Lake Superior,
Inflow and Infiltration. Inflow refers to clear water from rain and snowmelt that
improperly drains into the sanitary sewer system. Infiltration refers to ground water
that leaks into the sanitary sewer system through cracked or faulty sewer pipes.
Both sources of water are basically clean.
Why is I & I a problem?
Most communities around Lake Superior have two different sewer
systems. Sanitary sewers were designed to carry wastewater (containing
sewage) from homes and businesses directly to a treatment facility
where it can be cleaned before being released back into natural
bodies of water. Storm sewers were designed to handle rain and
snow melt that runs off the land and roads. This sewer drains
directly to area streams, rivers and Lake Superior and is not
During heavy rainstorms, I & I may cause the sanitary
sewers to quickly fill with clear rain water that should have been directed
to the storm sewer. When too much of this clear water mixes with
untreated sewage, the volume flowing through the sewer pipes may
exceed the capacity of the sanitary sewer system pipes. The result
is that water cannot reach the treatment plant to be cleaned because
the system becomes pressurized and essentially “blows” -
with diluted sewage backing up into basements or overflowing onto
streets. This dirty water then flows into area streams, rivers
and lakes. These overflows can lead
to exposure to untreated wastewater.
What causes I & I?
Old or cracked pipes may allow clear water to seep into the system
through infiltration. Private service lines from homes and businesses
may leak because of age, poor design or poor maintenance. Fifty-five
percent of Duluth’s sewer system is over 50 years old.
Another large source of water is inflow from roofs, foundation
drains and improperly drained sump pumps in area homes. Most homes
built before 1970 were designed with roof drains or foundation
footing drains that unfortunately direct rainwater into the sanitary
How did my basement grow? If
you own an old house, this might be how! Notice the FOOTING drain being
installed in the lower-left photo (taken in the 1940's). These footing drains were connected
to the sanitary sewer system, and are now one of the causes of overflow problems in Duluth.
While old footing drains are good at keeping water away from
the foundation of the house and help to keep basements dry, they are one of
the largest contributors of clear water to the sanitary sewer system. Footing
drains should be redirected to empty into a sump pit. The water can then be
pumped out by a sump pump into the yard where it can be dispersed into the
natural soil-groundwater and then flow harmlessly away in the storm sewer
What are the solutions to I & I ?
Cities are exploring many ways to reduce I & I around Lake
Superior. The City of Duluth’s I&I program seeks to remove clear
water through the installation of sump pumps and the disconnection of footing
drains from the sanitary sewer system. The program designates an area of the
city each year for mandatory inspection and disconnection. In some areas,
grant funding is available to help complete the necessary sump pump installations.
The City of Duluth also has a maintenance program to ensure that the sewer
pipes are in good condition.
City programs are important, but actions
by individual homeowners can also make a big difference.
Keep your sewer in good connection. Broken
sewer pipes (laterals) between the private home and the
city’s main line are usually the responsibility
of the homeowner. Keep it clean and do not plant bushes
or trees on top of it. Make appropriate repairs and replace
Make sure your home’s footing drains
are not connected to the sanitary sewer system. Install
a sump pump and discharge the water into your yard, away
from the house.
Ensure that your home does not have old
downspouts that drain directly into the sanitary sewer
system. Install gutters and downspouts that direct rainwater
away from your home’s foundation. Rain
Barrels and Rain
Gardens are inexpensive and attractive ways to help
landscape your yard so that water drains away from the