The City of Springfield’s Infiltration
and Inflow (I/I) Program works to maintain and improve the
efficiency of the City’s sanitary sewer collection system
and treatment plants and to prevent sewer overflow and backups.
Currently, 5 regular full-time and 15-20 contract personnel
perform infiltration and inflow reduction efforts.
What is Infiltration/Inflow (I/I)?
Infiltration occurs when groundwater enters the sewer system
through cracks, holes, faulty connections, or other openings.
Inflow occurs when surface water such as storm water enters
the sewer system through roof downspout connections, holes
in manhole covers, illegal plumbing connections, or other
defects. The sanitary sewer collection system and treatment
plants have a maximum flow capacity of wastewater that can
be handled. I/I, which is essentially clean water, takes up
this capacity and can result in sewer overflows into streets
and waterways, sewer backups in homes, and unnecessary costs
for treatment of this water. It can even lead to unnecessary
expansion of the treatment plants to handle the extra capacity.
These costs get passed on to the consumer.
Determining I/I:
Flow monitoring and flow modeling provide measurements and
data used to determine estimates of I/I. Flow meters are placed
at varying locations throughout the sewer collection system
to take measurements and identify general I/I source areas.
Measurements taken before and after a precipitation event
indicate the extent that I/I is increasing total flow. Both
infiltration and inflow increase with precipitation. Infiltration
increases when groundwater rises from precipitation, and inflow
is mainly stormwater and rainwater. Rainfall monitoring is
also performed to correlate this data.
Identifying sources of I/I:
A Sewer System Evaluation Survey (SSES) involves inspection
of the sewer system using several methods to identify sources
of I/I:
· Visual inspection - accessible pipes, gutter and
plumbing connections, and manholes are visually inspected
for faults.
· Smoke testing – smoke is pumped into sewer
pipes. Its reappearance aboveground indicates points of I/I.
These points can be on public property such as along street
cracks or around manholes, or on private property such as
along house foundations or in yards where sewer pipes lay
underground.
· TV inspection – camera equipment is used to
do internal pipe inspections. The City has one 2-3 person
crew that performs TV inspection on over 20 miles of sewer
pipe per year.
· Dye testing – Dye is used at suspected I/I
sources. The source is confirmed if the dye appears in the
sewer system.
Sources of I/I are also sometimes identified when sewer backups
or overflows bring attention to that part of the system. The
purpose of the SSES is to reduce these incidences by finding
sources before they cause a problem.
Repairing I/I sources:
Repair techniques include manhole wall spraying, insituform
pipe relining, manhole frame and lid replacement, and disconnecting
illegal plumbing, drains, and roof downspouts.
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