Environmental Services is designing pilot projects aimed at reducing the possibility of sewage overflows in parts of southwest Portland. In this part of Portland, pipes that carry sewage from homes and businesses can also fill with rain and groundwater during wet weather. This inflow (stormwater runoff) and infiltration (groundwater) is known as I&I and can cause sewers to back up through manholes or household drains. Releases from the sewer system threaten human health and the environment.
I&I also sends relatively clean water to the treatment plant and increases treatment costs. And the added stormwater and groundwater reduce the pipe’s capacity to carry sanitary sewage.
I&I is a problem in other parts of Portland, but especially in southwest Portland due to its unique geology, geography, and the lack of storm sewers.
Smoke-testing last summer located a number of cracked sewer pipes that allow groundwater infiltration and direct connections that allow stormwater inflow directly to the sanitary sewer.
The most successful efforts to control I&I in other parts of the country include partnerships between local government and private property owners. Making programs voluntary for property owners and providing financial incentives increase both participation and project success. For pilot projects in southwest Portland, Environmental Services will offer to repair or replace eligible privately-owned lateral pipes that connect properties to the public sewer at no cost to the property owners.
Pilot projects in Upper Hillsdale, Middle Hillsdale, and the area around SW Pendleton and 45th will help determine how effective different approaches are in reducing inflow and infiltration.
Upper Hillsdale Pilot Project
Work will start this spring on a pilot project in Upper Hillsdale to replace or repair public sewers in the street and private laterals that connect properties to the public sewer (see map below).
Environmental Services is designing two more pilot projects in middle Hillsdale and the area around SW Pendleton and 45th. Future pilot projects may disconnect downspouts, foundation drains and other stormwater connections from the sewer system. Participation in these pilot projects is entirely voluntary.
Why This Approach?
Three main reasons:
- Environmental Services has an agreement with the Oregon Department of Environmental Quality (DEQ) to eliminate frequent sewage overflows caused by I&I at SW Dewitt and 25th. Programs in other jurisdictions show that repairing or replacing private sewer laterals can reduce inflow and infiltration quickly and cost-effectively.
- The work will benefit sewer ratepayers citywide by reducing stormwater and groundwater flow to the treatment plant and avoiding additional treatment costs.
- If the pilot projects are successful, the city may avoid building an expensive separate stormwater system in southwest Portland.
Environmental Services staff will visit properties in pilot project areas to describe the work and discuss the opportunity to participate in the project. Regardless of participation, you will receive more information when a construction schedule is available.
Frequently Asked Questions (FAQ)
What is I&I?
I&I stands for inflow and infiltration. Inflow is the flow of stormwater into the sanitary sewer system through connections like roof drains, foundation drains, and basement sump pumps. Infiltration is groundwater seeping into sewer pipes, including private sewer laterals, through cracks and broken pipe joints.
Why is I&I a problem?
Stormwater and groundwater in sanitary sewers takes up space and reduces capacity in sewer pipes. So during rainstorms, increased I&I volume in sanitary sewers can cause sewage overflows onto streets and into local streams, or sewage backups through basement drains. I&I also increases flow to the treatment plant and increases treatment costs.
Why is I&I a problem in southwest Portland?
The sewer system installed in these neighborhoods half a century ago was designed to handle sanitary sewage, not stormwater. Managing stormwater runoff is challenging in southwest Portland because of steep slopes and slow-draining soil. So as development continued, properties often managed stormwater by connecting roof drains, basement sumps, and foundation drains into the sewer system either with or without permission from the county or city.
Since the City of Portland annexed the area many years ago, the city has been looking at the best ways to manage stormwater. Data collected from flow monitors in the sanitary sewer pipes show spikes or high flow volumes when it rains. Hydraulic modeling also shows that the sanitary sewer pipes don’t have enough capacity to handle sudden high volumes of stormwater or groundwater.
I&I can increase the volume in sewer pipes up to 100 times during a large storm. Removing I&I from sanitary sewer pipes is more cost-effective than installing larger sewer pipes or installing a separate stormwater collection system.
Why implement a pilot project now?
City investigations of sewer flows in parts of southwest Portland found a significant amount of I&I entering the sanitary sewer system. There have been several sanitary sewer overflows (SSOs) from a manhole near SW Dewitt and SW 25th Avenue over the past few winters. The Oregon Department of Environmental Quality (DEQ) has ordered Environmental Services to eliminate SSOs from the manhole at SW Dewitt within a specific timeframe or face significant fines.
Why repair or replace private sewer laterals?
Many other cities and counties have found that repairing or replacing private sewer laterals is the quickest and most cost-effective way to reduce I&I. An Environmental Services pilot project in 2013 will test this approach.
Once the pilot project is complete, Environmental Services will monitor sewer flows and continue hydraulic monitoring to determine whether additional projects are needed to reduce I&I. Participation in the pilot project is entirely voluntary.
How does I&I affect sewage treatment costs?
Because of I&I, the sanitary sewer pipes carry relatively clean stormwater and groundwater to the city’s treatment plants during wet weather. The sewage collection system and the treatment process can operate more efficiently by eliminating excessive stormwater and groundwater inflow and infiltration. This is a more cost-effective approach than increasing the size of sewer pipes and pumps to manage the extra wet weather flows.
What is the end goal?
The goal is to keep I&I out of sanitary sewer pipes. That will involve replacing deteriorated pipes, fixing cracks and bad pipe joints, fixing cracks in manholes, and disconnecting street stormwater inlets from the sanitary sewer. If it includes re-directing private downspouts, sump pumps and area drains, or fixing private sanitary sewer laterals, Environmental Services will work with property owners to find safe alternatives to manage the stormwater flows.
For More Information
Contact Joe Annett at 503-823-2934.