Inflow and Infiltration Reduction Program

Inflow and infiltration (I&I for short) are when stormwater and groundwater get into the sanitary sewer system. The City is undertaking an Inflow & Infiltration Reduction Program to rehabilitate the sewer system.

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. The sources of I&I are basically:

Inflow comes from stormwater collection systems (catch basins, roof gutters, etc.) that under looser standards many years ago, were connected to the sanitary sewer system.
Infiltration comes from groundwater permeating into breaks and cracks in sewer main pipes, laterals, and manholes.

Why We're Concerned About I&I

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.

Program Description

The City's sewer collection system has zones called "basins." The program includes:

Rivercrest Basin (10), mostly included within the Rivercrest Neighborhood. It's our pilot site because it's the smallest and simplest.
Linn Basin (8), includes parts of the Rivercrest and McLoughlin Neighborhoods. This is one of our current focus areas.
McLoughlin Basin (5), includes most of the McLoughlin Neighborhood and some of the Two Rivers Neighborhood. This is one of our current focus areas.
Falls Basin (5A), all of the Canemah Neighborhood and part of the Two Rivers and McLoughlin Neighborhoods. This is our next focus area.
Newell Basin (5B), parts of the McLoughlin and Elyville Neighborhoods. This is one of our current focus areas.
Warner Parrott Basin (12)
South End Basin (12A)

These basins are the most significant sources of I&I, but we may add other basins to the program in the future. Learn more about the basins in the program.

The program has five phases, described below.

Investigate

We’ll use these methods to find I&I:

Closed-circuit television, or CCTV, involves sending a robot with a camera through sewer mainlines. Technicians review the footage, rate the overall condition of each pipe, note the location and severity of any breaks or cracks, and identify any connections that don’t match with known sewer services.
Smoke testing involves blowing non-toxic chemical smoke into the sewer system. If smoke comes out of anything other than household sewer vents and manholes, we record the location and investigate further (usually with CCTV).
Dye testing involves pouring non-toxic dye into the stormwater system at locations such as catch basins and area drains. If we see the dye emerge in the sanitary sewer system, we record the location as a potential inflow source. Sometimes we work the other direction: We pour dye into the sanitary sewer system and watch whether it shows up elsewhere.

Identify Solutions

We'll decide how best to fix the I&I that we find:

We'll look at whether we can disconnect inflow sources from the sanitary sewer system and route them to the stormwater system. If no stormwater connection is nearby, we’ll consider adding one.
We’ll consider how to repair or replace pipes that have cracks and breaks where infiltration occurs.

Wherever we can, we’ll do this without digging trenches — by adding a liner to a pipe (cured-in-place pipe lining, or CIPP), pushing a new pipe through an old one, which bursts the old pipe (called “pipe bursting”), or by drilling a new pipe path underground (directional drilling). But sometimes we will need to dig trenches.

Learn more about the construction methods we'll consider.