Abating combined sewer overflow
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Installing new sewer lines on Tallman Street (2005)
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Much of Syracuse's sewer system collects both storm
water and sanitary sewage in the same pipes. During
dry weather these sewers carry all the sanitary sewage
to the Metropolitan Syracuse Wastewater Treatment Plant for treatment.
However, when rainstorms or snow melt increase the
amount of runoff, the combined flow of sanitary sewage
and storm water can exceed the capacity of the sewer
system. At these times, the sewers overflow and
discharge the excess—a combination of runoff and
sanitary sewage—into streams. This is
combined sewer overflow (CSO).
The sewer system was designed to overflow in this way
to prevent sewage from backing up into streets and
basements.
Combined sewer overflows add bacteria, floating trash,
organic material, heavy solids, and grit to city
streams and Onondaga Lake. Material from CSOs collects on
vegetation along and in streams. It looks bad and
smells bad, and it can also transmit disease to humans
who may come in contract with the water. Material from
CSOs also depletes the dissolved oxygen in the water
that is necessary for aquatic life.
About 50 years ago, Syracuse had ninety points where
sewage could overflow and reach Onondaga Creek, Harbor
Brook, or Ley Creek. At that time, the City of
Syracuse owned and maintained the sewerage system. The
City did not eliminate any of the overflows of the
combined sewers.
Onondaga County began to take ownership of the combined
trunk sewers and two interceptor (large) sewer lines
in the 1960s and ’70s. It immediately began making
improvements. In less than 30 years, it closed
permanently twenty-four overflow points.
Today
we have just 49 overflow
points, and that number will diminish further as
additional projects are completed.
 Click here to see progress on sewer separation in Syracuse.
CSOs are being addressed with several types of projects:
Regional treatment facilities
remove and/or store solids and floating material. They are also equipped to disinfect effluent to receiving streams if storage capacity is exceeded.
Sewer separation
divides combined sewer systems into individual sanitary sewers and storm sewers.
Floatables control facilities
remove floating debris with net bags, screens, or skimmer boats.
Learn more about the benefits of the new floatables control facilities.
Increased storage and transport capacity
optimize storage volumes in existing combined sewers and provide increased storage with new large conveyance pipes and underground tanks.
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Midland CSO Abatement Facility
Susan Miller, Project Deputy Director
Onondaga County Dept of Water Environment Protection