What is infiltration / inflow (I / I)?

Excess water that flows into sewer pipes from groundwater and stormwater is called infiltration and inflow or I/I. Groundwater infiltration seeps into sewer pipes through holes, cracks, joint failures, and faulty connections. Stormwater inflow rapidly flows into sewers via roof drain downspouts, foundation drains, storm drain cross-connections, and through holes in manhole covers. Most I/I is caused by aging infrastructure that needs maintenance or replacement.

Infiltration

Infiltration is groundwater, or groundwater that is influenced by surface or sea water, that enters sewer pipes (interceptors, collectors, manholes (MH), or side sewers) through holes, breaks, joint failures, connection failures and other openings. Infiltration quantities often exhibit seasonal variation in response to groundwater levels. Storm events can trigger a rise in groundwater levels and increase infiltration flows. The highest infiltration flows are observed following significant storm events or following prolonged periods of precipitation. Since infiltration is related to the total amount of piping and appurtenances in the ground and not to any specified water use component, it is usually expressed in terms of the total land area being served, or in terms of the lengths and diameters of sewer pipe. 

Inflow

Inflow is surface water that enters the wastewater system from yard, roof and footing drains, from cross-connections with storm drains, downspouts, and through holes in manhole covers. Inflow occurs as a result of storm events such as rainfall, snowfall, springs or snow melt that contribute to excessive sewer flows. Peak inflow can occur during heavy storm events when storm sewer systems are surcharged, resulting in hydraulic backups and local ponding. See the pictures on this page for a graphical view of the sources of inflow.

The additional water in the sewer system is a problem because:

• It takes up capacity in the sewer pipes and ends up at the wastewater treatment plant where it must be treated like sewage, resulting in higher treatment costs. These costs are then transferred to you, the user.
• Requires new and larger wastewater facilities to convey and treat larger volumes of flow, resulting in higher capital expenditures.
• I/I flows contribute to sewer system overflows into local homes and the area waterways, negatively impacting public health and the environment.

How do we locate Inflow & Infiltration (I / I)?

The primary method used to locate infiltration is by closed-circuit television inspection. During this process, a small robotic camera is placed inside the sewer main on a self-propelled crawler. The camera displays the internal condition of the sewer pipe to the camera operator who records any defects observed. The report and digital video of the inspection are then reviewed by an engineer who determines the appropriate repair needed for a given defect or defects present in the pipe. Additional methods used to locate I/I include manhole inspection, smoke testing, dyed water tracing, and internal building inspections.

How do we remove Inflow & Infiltration (I / I)?

There are many methods and technologies available to remove and reduce I/I. Assistance from the public by removing sump pumps, roof and perimeter drains from the sewer system can drastically reduce the amount of inflow. Modern techniques allow for the sewer lines to be inspected, cleaned, and even replaced or rehabilitated without traditional open-cut excavation. These "trenchless technologies" allow for rehabilitation and repair of sewers without the expense and interruption of conventional open-cut excavation. Not only is it more convenient to employ trenchless technologies to rehabilitate the sewer system, but it is also extremely cost-effective when compared to open-cut methods.

 

Sump Pumps and Downspouts Connected to the Sanitary Sewer Cause Big Problems

If you have a sump pump in your basement, you might think that connecting it to your home’s sewer line is a simple and effective way to get rid of excess rainwater. However, this practice is illegal and can cause major problems for both your home and the entire community’s sewer system.

Why Is It a Problem?

Sanitary sewer systems are designed to handle household wastewater only—things like water from sinks, showers, dishwashers, and toilets. They are not built to handle large amounts of groundwater and rainwater from sump pumps or downspouts. When these illegal connections occur, they overwhelm the sewer system, leading to:

• Sewer Backups – Excess water can cause sewage to back up into homes and streets.
• Increased Costs – Sewer rates are based on water usage, not on how much is discharged into the sewer. When large amounts of rainwater enter the system, it unfairly raises treatment costs for everyone.
• Overloaded Treatment Plants – When the system is flooded with rainwater, wastewater treatment plants must process far more than they were designed for, reducing efficiency and increasing expenses.

What Should You Do?

If your sump pump or downspouts are currently connected to your home’s sewer line, act now to prevent future problems. Call the Barre Sewer Department at (978) 355-5020, and we will work with you to find a legal and effective alternative for redirecting sump pump discharge away from the sanitary sewer system. .

 

To learn more about I&I or to have a free in-home evaluation, please contact treatment plant staff at (978) 355-5020