Frequently Asked Questions about Smoke Testing



The City of Framingham is conducting smoke testing to locate inflow and infiltration (I/I).


Inflow is rainwater or groundwater that enters the sewer system through a direct, piped connection or leaking manhole covers. It is clean water that does not need to be treated as wastewater.

Typical inflow sources include roof downspouts, sump pumps, and driveway drains that are connected to the sewer system. Leaking sewer manhole structures or covers located in low or wet areas are also sources of inflow.


Infiltration is groundwater that enters the sewer system through broken or leaking pipes or leaking sewer manholes. It is clean water that does not need to be treated as wastewater.

Inflow Diagram


Both infiltration and inflow can be estimated by installing flow meters in sewer manholes. Flow meter data is correlated to rainfall and groundwater levels.

Infiltration is identified through the inspection of sewer manholes and CCTV of sewer pipes. CCTV involves placing a TV camera into the pipe and recording the condition of the pipe. Flow isolation is also used to identify infiltration by measuring the flow during off-peak hours. 

Inflow is typically identified by conducting smoke testing, dye testing, or building inspections. Smoke testing involves introducing non-toxic smoke into the sewer pipe and noting if smoke protrudes comes out at roof leaders, catch basins, yard drains, or other potential inflow sources. Dye testing involves pouring a non-toxic, non-staining dye into the potential source and seeing if it appears in the downstream sewer manhole. Building inspections are when City personnel enters a building to verify whether a sump pump is improperly connected to the sewer system.


The City’s Wastewater Master Plan identified areas where flow metering data suggests inflow issues (i.e., flow increases in response to a rainfall event). The City is currently in a multi-phase, long-term plan to identify and remove sources of I/I in the sewer system. Previous efforts have included identification of potential inflow sources, dye testing, and closed-circuit television (CCTV) of sewer pipes.

When will smoke testing occur? 

Smoke testing is scheduled to begin Wednesday, September 1st. Testing is weather dependent and will occur Monday-Friday (excluding holidays), between the hours of 7 a.m.- 5 p.m. The entire testing program is slated to take approximately one month to complete.

WHERe will smoke testing be conducted?  

Testing will be conducted in western Framingham bounded by Pleasant Street, the Mass Pike, Route 9, Temple Street, and the Southborough town line. Reference the testing map plan for area specifics here. Testing will occur in between sewer manhole sections in both residential and business areas.

Who is conducting the Testing? 

Weston & Sampson, the City’s engineering consultant will be conducting testing. Company vehicles are black with the company name on the sides and their smoke testing personnel will be wearing shirts with the Weston & Sampson markings and will carry identification cards with them.  

How is smoke testing conducted?

Crews use specialized candles to create a non-toxic, non-staining smoke that is blown by a large fan into sewer manholes located on the road. By blowing the smoke into manholes, it enters the City’s sewer pipe system.  Crews will monitor where the smoke escapes and record their findings.

Do I need to be home when smoke testing occurs? 

No. You are not required to be at home during testing.

Should I do anything to prepare for smoke testing? 

Weston & Sampson recommends businesses/residents to pour two gallons of water down any floor drains or unused plumbing fixtures. Dry traps(bend in piping under the fixture) cannot perform their function properly. By pouring water in the drains, the traps will be restored, and avoid the possibility of smoke entering your dwelling. Smoke should not enter your premises unless there is a dry trap in an unused fixture or a plumbing defect. 

Sink Trap 101 - Graphic
Image of a sink and faucet with a pipe that bends in towards the wall.

Text: Sink Trap 101

An arrow pointing to sink.

The piece of plumbing fixture is highlighted green. Text: Waste goes down the pipe from the sink.

The bend in the pipe is blue. Text: Water is captured here (bend in the pipe) when the sink is used to block sewer gases, known as the "trap".

The plumbing pipe is highlighted yellow. Text: Sewer gas from wastewater. 

Will smoke enter into my home/business when testing occurs?  

Smoke should not enter your premises unless there is a dry trap in an unused fixture or plumbing defect.  It is a good common practice to avoid letting your trap dry out (by running the sink or pouring water into the drain) to avoid sewer gases from potentially entering your home.

I have animals in my home. Should I be concerned about my pets when smoke testing occurs? 

If you are concerned about smoke entering your home place your pets in a well-ventilated room and leave the windows open.

What will I be able to see when smoke testing occurs? 

Residents will be able to see smoke exiting out the vent stack on their home or building. Vent stacks allow sewer gas to exit. Smoke will also be visible from sewer manholes in the street.

Can smoke testing set off fire alarms? 

If smoke is to enter your home, yes, it is possible for your fire alarms to activate.

Can smoke testing set off indoor sprinkler (Fire Suppression) systems? 

It is highly unlikely. Typically, indoor sprinklers (fire suppression systems) are activated by heat, not smoke. 

Smoke has entered my house/business. What should I do? 

If smoke enters your home, please notify the Weston and Sampson field crew right away. It is recommended that you open your windows to ventilate the area. The crew will be visible outside your home/business. If concerns arise, please walk outside and talk to the crew.

WIll residents and businesses be notified prior to testing? 

Yes. Doorhanger notifications are planned to be dropped off two days prior to testing. Testing is weather permitting. An anticipated schedule is available on the City’s website:

If inclement weather occurs, you may receive another door hanger two days prior to testing. 

Will there be any traffic impacts when testing occurs? 

Minor traffic interruptions may occur during testing.  

I received a notice about smoke testing in my neighborhood and I have respiratory problems. What should I do? 

If you receive notification of smoke testing in your neighborhood and you have respiratory issues, such as emphysema or asthma, please notify Weston & Sampson at (508) 250-0245. Please leave a message in the voicemail box, including your name, address, and contact telephone number, and your call will be returned promptly.

What type of product is being used to conduct smoke testing? Is the product being used potentially hazardous to my health? 

The smoke product used is non-toxic and non-staining. Reference specific product information here. Although the smoke is non-toxic and non-staining, it is capable of causing irritation, especially to those with lung ailments such as asthma or emphysema. It is important to notify Weston & Sampson at (508) 250-0245 if you have health concerns and/or respiratory issues, such as emphysema or asthma. Please leave a message including your name, address, and telephone number and your call will be returned promptly.

How is I/I Removed? 

Infiltration caused by broken or cracked pipes or manholes can be removed by either replacing or rehabilitating the infrastructure. Inflow caused by leaking manhole covers can be removed by replacing the cover, or installing waterproof covers in low, wet areas. Inflow caused by improper drain or sump pump connections can be removed by re-piping the discharge of the source.

Why is it important to remove infiltration & Inflow (I/I) Sources? 

The City is required by the Massachusetts Department of Environmental Protection (MassDEP) to identify sources of rainwater runoff and groundwater that enter the sewer system. The City pays the Massachusetts Water Resource Authority (MWRA) for every gallon of water that enters the sewer system regardless of its source. Removal of inflow to the sewer system will reduce sewer capacity and overflow issues, protect surface water quality, and decrease the City’s sewer costs.

For more information about the Inflow/Infiltration Source Removal Program, please contact:
Alison Eliot, Senior Project Manager