I/I: The Elusive Terror to Wastewater Systems

Wastewater | Sanitary sewer manhole cover

What is I/I?
I/I stands for Infiltration and Inflow. Infiltration, also known as groundwater, seeps into sewer pipes and manholes through defects. These defects can be because of aging infrastructure and materials or improper installation during construction. Inflow occurs when groundwater or stormwater seep into the wastewater system through either private or public defects, such as storm drains or downspouts connected to the sewer system.

Since 2008, our region has seen annual precipitation exceed the long-term average every year except for four. (National Centers for Environmental Information)

Have you ever taken the time to think about where all that water goes?

The last place a municipality would like to find it is in their sewer system. A single leak in a joint of a manhole or pipe could potentially allow up to 7,200 gallons of water into the sewer system in a single day. A municipality typically has miles of sewer main and potentially hundreds of manholes that could allow water in through these types of leaks.

It’s just rain water, what is the harm of that?

A manhole overflowing after a major storm event.
A manhole overflowing after a major storm event.

The problem is that treatment facilities are designed with a specific set of influent wastewater characteristics, storage, and treatment capacities, all of which have the potential to be completely altered when extra water seeps into the system.

Treatment plant design is often based on the anticipated number of users, flow volume, and peak design flow. If the I/I exceeds the peak flow of the treatment plant and system, sewer system overflows (SSO) – which involve the release of untreated or partially treated sewage – can occur. Raw sewage contains bacteria, viruses, protozoa, helminths, mold, and fungi which can have various health effects on the public. If the peak design of the treatment plant and sewer system is exceeded, the sewage can overflow at the treatment plant, backup in sewer lines, or even potentially backup into a low-lying house service lateral or basement.

The fight against I/I is a constant battle. With miles of sanitary sewer mains and hundreds of manholes, how do you stay on top of the issue? Or if you are already experiencing SSOs, how do you find the issue?

“Working with Klingner in the past four years, I have found that they are very responsive and helpful. That is important for me because time is often directly related to the overall cost of a particular project. They have been courteous, timely with their responses, and willing to adapt to this District’s needs.”
— Lucas Drullinger,
District Manager of PWSD#1 of Ralls County, MO

Klingner breaks this battle down into four basic stages to locate, correct, and prevent I/I issues: Narrow, Test, Assess & Correct, and Prevent.

  • NARROW | Dividing the sewer system into smaller zones helps us narrow the scope of search. Using flow monitoring equipment at strategic locations, Klingner collects data for both dry and wet weather conditions. The data will show an increase in flows during, and in the days directly following, the rain event. If the flow increases only during, or immediately following, rain events, then I/I is getting into the system in those zones.
  • TEST | Smoke testing can be used to determine specific defects in the sewer lines. Smoke testing is the process of blowing non-toxic smoke through a sewer main and documenting the locations where the smoke reaches the surface. This method focuses on narrowing down inflow areas.
  • ASSESS & CORRECT | Once the lines in the zones affected by I/I have been smoke tested, we do a more detailed assessment via televising and video recording. By analyzing televised sewer mains, our engineers can more adequately determine whether the main can be fixed through the use of Cured In Place Pipe (CIPP) Lining, a specific point repair of the defect, or if it needs to be replaced. This method focuses on narrowing down infiltration areas.
  • PREVENT | To prevent I/I problems moving forward, Klinger recommends that our team remains involved during construction to catch any defects in the installation of pipe and manholes. We also suggest municipalities take a proactive approach by keeping track of lift station pump hours to determine if additional flow is being encountered following rain events and maintaining proper sewer main maintenance, log of corrections, and updated mapping.

The fight against I/I may seem insurmountable, but with a focused approach, any municipality can maintain a healthy system.

Smoke testing revealing a point of inflow.
Smoke testing revealing a point of inflow.

Joshua Hartsock

BY JOSHUA HARTSOCK, PE
Columbia, MO