Inflow & Infiltration

I & I: What is it?

Inflow and infiltration are terms to describe how groundwater or storm water illegally enters a sanitary sewer system.

Inflow is storm water 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 ground water that 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 20-50 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 is it a problem?

Sanitary sewer pipes are designed to carry water that is flushed down the toilet, or washed down the drain, shower, dishwasher. These pipes have a specific carrying capacity designed only for this sewage. When storm water or ground water also enters the pipes, the total flow increases and it can cause deterioration of the pipes and also back-flow and flooding in homes and businesses. This is detrimental to the wallets and heath of residents whom it effects.

It is also a problem because when storm water and ground water enter, 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.

What are we doing about it?

Here at the Borough, we have taken measures to reduce the total amount of inflow and infiltration into our sanitary sewer pipes.

The first step in doing something about I & I is metering the pipes at different locations. Meters measure the flow of the pipes and can tell us what the normal flow is and tell us when there is an increase, or spike in flow. A spike in flow means that something abnormal is taking place. Sometimes, when spikes correlate to rain events, we can infer that there is an infiltration problem with the pipe.

IMG_1620 A.jpg
Red arrow designating normal flow
Blue arrows designating leaks

The graph below shows data from meter readings in the sewer pipes during rain events of Summer 2013. There is a clear correlation between rain events and increase in flow and the location of the meters.

Inflow and Infiltration 2013

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