Inflow and infiltration (I&I for short) are when stormwater and groundwater get into the sanitary sewer system. The City has an Inflow & Infiltration Reduction Program to rehabilitate the sewer system.
Infiltration & Inflow: What Is It?
Inflow is stormwater that would originally enter the storm drain and pipes but instead enters the sanitary sewer pipes at a direct point location. Examples of this would be an inlet, roof drains, drains from driveways, or sump pumps from basements that are illegally connected or diverted to an area that is connected to a sanitary sewer pipe.
Infiltration is groundwaterthat seeps into cracks and leaks in sanitary sewer pipes at some location underground. Cracks or leaks in sanitary sewer pipes can be due to age and deterioration, poor design, loose joints, or maintenance errors. Average sewer pipes are designed to last about 20 to 50 years, depending on what type of material is used. Often sanitary sewer system pipes, along with the lateral pipes attached to households and businesses, have gone much longer without inspection or repair and are likely to be cracked or damaged.
Why It’s a Problem
Sanitary sewer pipes are designed to carry water that is flushed down the toilet or washed down the drain, shower, or dishwasher. These pipes have a specific carrying capacity designed only for this sewage. When stormwater or groundwateralso enters the pipes, the total flow increases, and it can cause deterioration of the pipes and also backflow and flooding in homes and businesses. This is detrimental to the wallets and health of residents whom it affects.
It is also a problem because when stormwater and groundwaterenter, they become contaminated with the other sewage flow. First, this is detrimental to the streams that would’ve otherwise received this clean water, and second, it increases the volume of water that needs to be treated, which costs money to the residents and municipality.
How to help reduce Inflow and Infiltration
* Disconnect downspouts: Ensure downspouts are directed to flow away from the home’s foundation, not into the sanitary sewer system.
* Check basement drains: Verify that basement and foundation drains are not improperly connected to the sanitary sewer.
* Maintain sewer lines: Homeowners are responsible for repairing defective or broken sewer pipes on their property.
* Report issues: Residents can report suspected I&I problems to their local municipality.
Why We’re Concerned About Inflow and Infiltration
I&I can lead to sewer overflows during and after heavy storms, when flows can be 10 times greater than normal. Overflows could damage household basements, overload wastewater treatment facilities, and pollute the Willamette River.
I&I could require spending on oversized pipes, pumps, and similar infrastructure to prevent overflows—because whether in the sewage collection system or in the Willamette River, overflows are unhealthy and prohibited by the Federal Environmental Protection Agency (EPA) as part of the Clean Water Act. Also, infrastructure wears more quickly and increases maintenance costs when exposed to high flows.
Limiting I&I preserves health and safety and saves ratepayers money. That’s why the city has a program to find and reduce it.
Case study
Inflow and Infiltration (I/I) Reduction Study
The Town of Newmarket is working with Civica Infrastructure Inc. on an Inflow and Infiltration (I/I) reduction study. The study’s objectives are to identify sources of I/I entering the sanitary sewers and to develop a plan to reduce these “extraneous” flows. A flow monitoring program with field testing is being conducted to identify sources of I/I entering sanitary sewers. The flow monitoring program will identify general areas within the Town of Newmarket that have increased I/I. Additional field testing will then be conducted in these areas to identify the specific sources of I/I.
Conclusion
The problem of Inflow and Infiltration (I&I), where stormwater or groundwater enters the sanitary sewer system. Inflow occurs when water directly enters through points like roof drains or illegal connections, while infiltration happens through cracks or damaged underground pipes. This leads to flooding, increased treatment costs, and river pollution. Solutions include disconnecting downspouts, maintaining sewer lines, and reporting issues to local authorities.
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References
1- Sewer Repairs – Inflow & Infiltration Reduction Program
Sewer Repairs – Inflow & Infiltration Reduction Program | Oregon City, OR
2- Inflow & Infiltration
https://www.statecollegepa.us/355/Inflow-Infiltration#
3- Inflow and Infiltration
