Sanitary Sewer Smoke Testing

In the coming weeks, the Public Works crew will be conducting smoke tests on sections of our sewer system. These tests help the City identify how and where water (and other material) enters and leaves our sewer system, allowing us to locate defective connections and spots in need of repairs.

During smoke testing, field crews blow air and smoke into the sewer system from the street and then monitor where it comes out. The smoke under pressure will fill the main line as well as any connections and then follow the path of any leak to the ground surface, quickly revealing the source of the problem.

For instance, if smoke permeates up through a yard, it indicates breaks in the sewer line. The smoke is gently pushed to overcome atmospheric pressure and  should escape from building roof vents.

The smoke itself is actually not smoke, but a non-toxic, non-staining odorless vapor.

Smoke testing is a harmless, cost-effective way to identify areas of our sewer system that need improvement.

Below are some common questions and answers about this testing, if you have any further questions, please call the Public Works Department at (360) 384-4006.

  • 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.

  • Will smoke testing of the sewers allow smoke to get into my home?

    No, provided that your plumbing is installed and functioning properly, and provided “traps” are filled with water. Drains that are used frequently should be okay. If you are not sure, simply run water down the drain for a minute to ensure that the trap is not dry. It is important to locate dry traps as they could allow sewer gases to enter the home. Dry traps are most commonly found in basement floor drains that are used only during rare flood events or in unused fixtures. Please thoroughly check your home.

  • What does it mean if smoke enters my house?

    If smoke enters your home during the test, it may indicate there are deficiencies in the plumbing that may allow potentially dangerous sewer gas to enter.

  • How may the smoke enter my house?

    Since plumbing fixtures in your home or business are connected to the sanitary sewer system, there is the potential for the smoke to enter if the drains are not connected properly. This happens particularly under the following circumstances:

    • The vents connected to your building’s sewer pipes are inadequate, defective or improperly installed
    • The traps under sinks, tubs, basins, showers and other drains are dry, defective or improperly installed
    • The pipes, connections or seals in the wastewater drain system in and/or under your building are damaged, defective, have plugs missing or are improperly installed.
  • What should I do if smoke gets into the house?

    • Do Not Become Alarmed
    • Open windows to allow ventilation and note the location of the smoke emission; smoke will clear within a few minutes
    • Exit the building and notify smoke testing personnel in the area.

    We recommend evacuating as a precautionary measure in case the smoke is due to a real fire rather than a test, and also since smoke in your house from this test indicates other sewer gases may also be entering the building.

  • How is a plumbing “trap” supposed to work?

    The “gooseneck” or “snake” section of your drain pipe is the “trap.” The trap allows water to fill that section of the pipe completely. Since vapor and gas cannot travel through water unless under pressure, this effectively “traps” the gas in the sewer portion of the pipe. The vent on your system— the portion of pipe protruding from the roof of the building—prevents the gas from becoming pressurized and allows it to escape outside the structure. These two systems function together to keep potentially harmful sewer gases from entering your structure. If there is no water in the trap, the trap is not functioning properly. We recommend dumping water into building drains and fixtures prior to testing.

  • How long will the testing take?

    While crews might be in your area for a few hours, each actual smoke test setup takes approximately 15 minutes to complete. Most houses will only be within the testing area for one or two tests.

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

    The purpose of the smoke test is to identify sources of unauthorized water entering the public portion of the sewer system. While it is also beneficial to note deficient plumbing connections on private property, this is not the main intent of the smoke test. It is the homeowner’s responsibility to maintain private plumbing connections.

  • Why can’t you tell me in advance exactly what date my home will be tested?

    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.

  • Can the smoke testing activate the smoke alarms?

    Yes, smoke alarms may be activated during smoke testing. If possible, open windows and/or doors for ventilation. If you have any doubts about the origin of the smoke, please call 911.

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