Infiltration and Inflow: A Complete Guide

Sanitary sewer systems are designed to move wastewater from homes and businesses to your area’s treatment facility. However, leaks in the sewer system and manholes, along with illegal connections, can cause groundwater to enter the system. These processes are called infiltration and inflow.

While a little water might not seem like an issue, stormwater and groundwater can cause major problems for your sewer system and wastewater treatment facility. Let’s explore how and why.

What Are Inflow and Infiltration?

Infiltration is the process of clear groundwater seeping into sewer pipes. It most often occurs when sewer pipes have holes, cracks, or faulty connections, allowing the water to leak in during periods of groundwater saturation.

Inflow, by contrast, is when stormwater flows into sewers through downspouts on roofs, storm drains, and manhole covers.

Both inflow and infiltration in sanitary sewer systems can cause problems, largely because many municipal systems and water treatment plants aren’t designed to handle relatively clean stormwater. They can also cause overflows and lead to expensive equipment failures.

What’s the Difference Between Infiltration and Inflow?

The primary difference between infiltration and inflow is how they happen.

Infiltration tends to occur slowly. It can happen as equipment gets worn out with continued use, due to gradual shifts in the soil, erosion, or other factors of nature and time. However, it can also cause existing issues to become more severe.

Inflow, by contrast, tends to happen all at once—most often during periods of heavy rain or severe weather events. It can contribute to disastrous consequences both for municipal infrastructure and homeowners connected to the sewer system.

Why Inflow and Infiltration Are a Problem

Lift Station and Other Malfunctions

Both infiltration and inflow can cause equipment and pipes to malfunction or even break during backups. Since repairing and replacing things like lift stations can be costly, infiltration and inflow can lead to a small problem costing hundreds of thousands of dollars. 

Sanitary Sewer Overflows

Combined or separately, infiltration and inflow can lead to the system becoming backed up, causing sewers to overflow onto the streets or even into people’s homes. This can lead to severe weather events becoming major issues that cost both the city and its residents thousands of dollars in repairs and cleanup costs after an overflow occurs.

Environmental Issues

Infiltration and inflow can cause serious environmental hazards when left unaddressed. When sewer pipes experience either issue, it can cause raw sewage backups and overflows, releasing potential pathogens into local waterways and habitats adjacent to the sewer system. In turn, this can also cause public health issues like norovirus, cholera, and other outbreaks associated with untreated sewage.

How to Address Inflow and Infiltration

Mass Flow Monitoring (MFM)

One of the first steps in reducing inflow and infiltration is using flow monitoring to identify and prioritize problem areas that need to be addressed. F&V uses a specialized technique called Mass Flow Monitoring (MFM).

With MFM, we install flow monitors at multiple manhole locations to differentiate and estimate the extent of the inflow and infiltration issues. This allows you to see more location data with better cost-efficacy.

We can easily deploy MFM through small or large portions of your sewer system to locate infiltration and inflow points, making them easier to monitor and address with further field investigations.

Closed-Circuit Television Surveillance

Closed-circuit surveillance uses fiber optic cameras to provide a visual understanding of your sewer system’s condition. A NASSCO Pipeline Assessment-certified inspector guides the camera through the pipeline to find potential infiltration and inflow problem areas.

The camera has radio transmitters that record the depth and location from the surface. This allows you to know exactly where the defects are, without having to survey the entire sewer system all at once.

Smoke Testing

Smoke testing involves pumping nontoxic, odorless smoke into the sanitary sewer system. With equipment setups in manholes at strategic locations, crews can closely monitor where smoke emerges from the sewer system. For example, if a service lateral is broken, smoke will emerge from it, allowing you to easily find where the problem is.

Our experts will document any areas of concern and include them with supporting data and photos in a report, along with recommended rehabilitation methods. For example, some may recommend trenchless cured-in-place liners and pipe bursting, which repairs joints and manholes.

Structure, Plumbing, and Sump Pump Inspection

In addition to monitoring the structure of the sewer system itself, some municipalities will implement rules or inspect residential sump pumps to make sure they’re not adding further stress to the sanitary sewer system. This can be done during other types of inspections to ensure that sump pump setups are connected to either a storm sewer or feed into the home’s yard.

Similarly, ensuring that residential and commercial plumbing systems are properly connected to the city’s sewer system can also prevent major infiltration issues.

Get Effective Inflow and Infiltration Solutions with F&V

F&V has both experience and state-of-the-art tools to address infiltration and inflow issues, keeping heavy rain from becoming a problem. Connect with our experts today to see how we can save your community time, money, and frustration.