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 has an Inflow & Infiltration Reduction Program to rehabilitate the sewer system. The sources of I&I are basically:
- Inflow comes from stormwater collectors (catch basins, roof gutters, etc.) that were connected to the sanitary sewer system.
- Infiltration comes from groundwater permeating into breaks and cracks in sewer pipes, and manholes.
Why We're Concerned About I&I
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.
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.
The City's sewer collection system has zones called "basins." The program includes:
- Rivercrest Basin (10), is mostly 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) is 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.
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 mist into the sewer system. If mist 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.
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.
We’ll evaluate the solutions we considered and plan how to carry them out as projects. This will include engineering plans, specifications, and cost estimates. We'll also get input from residents, property owners and neighborhood associations on how to reduce construction impact.
We’ll advertise for and select contractors in compliance with state and local rules and regulations. Once we award a contract and set a schedule for a project, we’ll notify the public before we start it. We’ll oversee construction to ensure compliance with standards and verify that the work will fulfill its intended purpose.
We’ll collect CCTV footage for all finished projects and verify that a basin’s sewage collection system has been restored to good condition.
We’ll monitor flow at key locations and compare it to records from before a project. We’ll also compare against maintenance records to assess whether maintenance is less extensive and less frequent.
The City adopted the Sanitary Sewer Master Plan in November 2014. The plan identified areas with excessive I&I. A follow-up study in February 2020 listed projects (with cost estimates) that would reduce I&I in some of these areas. The five-year budget proposed in the study totaled $10 million, divided relatively evenly between each year.