2023/2024 I&I Programming

Description: The 2021 Sewer Utility Capital Improvement Plan Update highlighted the need for a comprehensive wastewater collection system rehabilitation program to reduce Inflow and Infiltration (I&I). I&I refers to the unintended entry of groundwater and stormwater into sanitary sewer systems. Inflow occurs when clear water flows directly into the system from sources such as roof drains, basement sumps, and manhole covers. Infiltration happens when groundwater seeps in through cracks and joints in the sewer pipes. Excessive I&I can lead to sanitary sewer overflows and strain wastewater treatment facilities.

By mitigating unwanted flows at the Wastewater Treatment Plant (WWTP), we can minimize system flow spikes during the wet season (October 1 - May 30), thereby preserving treatment plant capacity and avoiding the costs associated with processing clean water. The Capital Improvement Program (CIP) has divided the I&I Program into two distinct projects: long-term/annual program planning and construction:

• CP-1: Infiltration and Inflow Program: On-going Citywide program to identify Infiltration and Inflow issues throughout the City’s collection system (monitoring, inspection, etc.)
• CS-1: Infiltration and Inflow Repair: Address found I&I issues (CIPP, injection grouting, pipe replacement, lid replacement, etc.)

Current Progress: In 2023, the City began monitoring flow at four locations throughout Old Town in preparation for this I&I program, collecting flow data through July 2023. Parametrix and their subconsultants reviewed the data and concluded there is a heavy presence of I&I in Old Town between Taylor Street and Stella St. This area was smoke tested in early 2024 to look for stormwater entry locations and CCTV the most offending areas. 

Staff provided an update to City Council on the I&I report and next steps at the January 16, 2024 City Council Meeting.
City Council Presentation PowerPoint
Draft I&I Report

Smoke Testing

Smoke testing is the industry standard method of identifying sources of inflow and infiltration into a sanitary sewer system. Identifying locations are the first steps in reducing influent to our local wastewater treatment plant.

A Smoke Test uses non-toxic smoke and high capacity blowers to blow smoke through the sanitary sewer pipes. In the image below, a blower is placed on top of a manhole, forcing smoke down into the sewer. If smoke is exiting the ground where there is no connection to the sewer lines, this indicates a place where rain/surface water and/or ground water could enter the sewer system. During a smoke test, a work crew will walk the neighborhood, take pictures of any faults in the system where smoke is coming out of the ground, and mark locations for repair. Common locations where unwanted water may enter our system include: unconnected sewer lines, leaking manholes, broken laterals or mains, cross connected lines, roof downspouts, yard/foundation drains, and sump pumps.

What to Expect

Smoke will not enter buildings unless there is defective plumbing or dried-up drain traps (aka pea traps), which are common in all household plumbing systems. It is expected – and normal – for smoke to come out of the sewer vent stack on the roof of a building during the test. The smoke is non-toxic, creates no fire hazard, leaves no residue, dissipates quickly and is harmless; however, those with respiratory issues may wish to take extra precautions, such as leaving the area for a few hours until testing is complete. The smoke can activate smoke alarms, so please take notice.

Video summarizing the process: https://youtu.be/8WiogXes3dU

Common Questions from Residents

Q: What do I do if I see smoke?

You should always feel free to call 9-1-1 in an emergency. If you believe smoke is entering your home from the smoke testing, simply open doors and windows and the smoke will dissipate quickly. Also, please contact a member of the Bravo crew if they're still on your street so your house and can be identified and addressed. If the crew is no longer in the area, please contact the City's Project Manager, Ben Ressler, at 425-939-8046.

Smoke in your house could be an indication that:

• The vents connected to your home’s sewer pipes are inadequate, defective, or improperly installed.
• The traps and seals under sinks, showers, tubs, toilets, and all other drains are dry, defective, or improperly installed.
• The pipes, connections, or seals in the wastewater drainage system or under your home are damaged, defective, are missing plugs, or are improperly installed.

If all sewer connections are working properly and there are no open faults in the home, all smoke should run through the sewer lines and out the building’s roof vents. This is normal.

Note: In the event of smoke entering the home means there is an open fault, where sewer gas has been entering the home for months or years. This sewer gas is poisonous and highly dangerous to residents. You should then call a licensed plumber and repair the fault as soon as possible.

Q: Is the smoke hazardous?

No.  The smoke is non-toxic and harmless.  It is light in color, leaves no residue, and does not create a fire hazard. People with particular respiratory sensitivity should avoid exposure to all types of smoke.

Q: How should I prepare for a Smoke Test?

Prior to testing date, pour ½ gallon of water in all basement floor drains or seldom used sink/shower drains and be sure to flush any seldom used toilets.  This ensures that drain traps (pea traps) are filled with water and smoke will not enter the house through any normal, working sewer-line connections. As demonstrated in the photo below, this “traps” water in the pipes, and is called “filling your traps.

Q: Do I need to be home during a Smoke Test?

No, homeowners do not need to be home during testing.

Q: I am a pet owner and I will not be at home during the testing. Should I be concerned?

The smoke is not harmful to pets. As long as windows are left open, any smoke that enters the building will dissipate in a few minutes. That said, do not leave pets unattended in a confined space.

Q: How will I know if smoke enters my house if I am not home during testing?

The purpose of Sewer Smoke Testing is to identify improper sources of water entering the public portion of the sewer system. While it is also beneficial to identify deficient plumbing connections on private property, this is not the main intent of the testing and it is the responsibility of the homeowner to maintain the plumbing on their private property.

Q: Will Smoke Testing the sewers allow smoke to get into my house?

No, if your plumbing is correctly installed and functioning properly, and your “traps” are all filled with water, then no smoke should enter your home. Very few homes typically get smoke in them from sewer smoke testing.

Q: If the smoke is harmless, why is it recommended to evacuate the building?

This is a precautionary measure in case the smoke is due to a real fire rather than the sewer testing, and also because smoke from the sewer testing indicates that dangerous sewer gasses are also entering the home. Although the testing smoke is not toxic, dense smoke or prolonged exposure can be irritating to mucus membranes so it is always best to minimize exposure.

Q: Can the Smoke Test activate the smoke alarms?

Yes, smoke alarms may be activated by testing. Open windows or doors for ventilation if possible.

Q: What does it mean if smoke is in my yard or driveway?

This could mean that a drain on the property is connected to the sewer lateral or that the lateral has breaks or cracks in the pipe, causing drain runoff that contributes to sewer backups and overflow.

Q: Am I responsible to fix identified I&I locations on my property?

Yes. Per DMC 9.04.130, homeowners are required to maintain their side sewer connections to the mainline. This includes addressing and resolving I&I locations. Please contact Ben Ressler to discuss options and expectations. 

Q: Why can't you tell me in advance exactly what date my home will be testing?

This testing cannot be conducted during rainy periods or very windy conditions, so it can sometimes be delayed. Also, other activities in the project may take less time than anticipated, so it can sometimes be sooner than expected. The schedule may also shift if more or fewer defects than expected are located and need to be documented.

Project Manager:
Benjamin Ressler
425-939-8046
benjamin.ressler@duvallwa.gov