TriCo Regional Sewer Utility

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Inflow & Infiltration

Inflow & Infiltration Program (I/I)

More About Inflow and Infiltration

INFLOW is rainwater that enters the sanitary sewer system directly from downspouts, street storm systems, and improperly plumbed sump pumps.
INFILTRATION is rainwater, groundwater, or springs that enter the sanitary sewer collection system after filtering through the ground. Infiltration sources are generally cracks in sewage pipes or manholes, and building foundation drains illegally connected to the sanitary sewer.
Like most municipalities, the Utility has a combination of clear water I/I problems. Evidence of combined I/I is noticed at the Utility's wastewater treatment plant (WWTP), where the sewage flow rate increases immediately during a storm event and continues at elevated conditions for several days after the storm event. The immediate flow increase is due to inflow and the continued elevated flow rate is due to infiltration.
Elevated flows in the collection system can exceed the sewer main's capacity to get the sewage to the WWTP. When the sewer pipe capacities are exceeded, sewage may overflow at locations such as manholes, lift stations, and basements. These overflows allow raw sewage to bypass the treatment process and pollute the environment. It also increases the risk of humans coming into contact with potentially hazardous waste. Over the years, the Utility has had to increase capacity in the collection and treatment systems to accommodate not only growth in the customer base but inflow and infiltration. In 2005 alone, over $4 million was spent on capacity upgrades at the pumping station located at Springmill Road and 106th Street.
Removing Inflow/Infiltration will...
  • Add capacity to the sanitary sewage collection and treatment systems.
  • Help eliminate pollution to the environment.
  • Help eliminate human contact with raw sewage.
  • Help the Utility comply with State and Federal regulations.
Downspouts and sump pumps illegally connected to the sanitary sewer system can be a huge source of clear water inflow. Therefore they cannot be connected to the sanitary sewer. Since Clay Township receives an average yearly rainfall of 36-inches, one residential house with 2,000 square feet of rooftop can contribute approximately 45,000 gallons of clear water to the sewage systems each year if their downspouts are connected. This equates to a yearly cost of approximately $92 per house to treat rain water. 

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Ryan Hartman
Ryan Hartman,
District Engineer

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