Some examples of the impact that Inflow and Infiltration may cause are as follows:

• Pump stations handling large volumes of unnecessary water
• Hydraulic overloads that will greatly reduce system efficiency
• Increased operating expenses due to the processing of ground water and storm water that do not require treatment
• Unnecessary equipment wear
• Increased collection system maintenance and cleaning

There are a few factors to consider when deciding if implementing a smoke testing program will be beneficial to your Facility.

What is the age and type of materials used in the collection system? Many sanitary systems are 50 to 100 years old and are constructed of out-dated materials. Over time decay and roots cause breaks in the lines that will permit excessive infiltration during wet periods.

The presence of undesired connections such as basement and yard drains, catch basins, cross connections from storm sewers, foundation drains and roof down spouts will cause elevated flows every time it rains. The easiest way to tell if this exists in your collection system is to have a look at the plant’s influent flow meter.

Smoke testing is a very quick and easy way to determine if buildings are properly connected to your system. Smoke should exit the vent stacks of the surrounding properties within the testing area. If traces of the smoke or its odor enter the building, it is an indication that gases from the sewer system may also be entering. Smoke that enters a building can cause panic and stress to an unsuspecting individual. This will require some good public relations skills and allow for an opportunity to stress the importance of correcting the problem. Remind them that the smoke entering their building is their friend. If smoke is entering their home or business, DANGEROUS gases could be entering as well. The smoke that is manufactured specifically for testing is not dangerous or toxic, leaves no residuals or stains, and has no effects on plants or animals. It has a distinctive, but not unpleasant, odor. The visible smoke and odor will only last for a few minutes, where there is adequate ventilation. Sewer gases are dangerous! A few of these gases have no odor and present the most serious problem because they can enter a building undetected. These gases can cause anything from minor illness to death. Identifying and correction of the source of any smoke entering a building is urgently advised.

Possible causes for this smoke entering the building are:

• The vents connected to the building’s sewer lateral are inadequate, defective, or improperly installed.
• The traps under sinks, tubs, basins, showers, floor drains, etc. are dry, defective, improperly installed, or missing.
• The pipes, connections, and seals of the building’s sewer system are damaged, defective, have plugs missing, or are improperly installed.

In the end, if the situation is handled properly, the property owner is usually grateful for the assistance and information that you provide.

Smoke testing can also be very useful in locating "lost" manholes. Although collection systems can cost millions of dollars they are often the first thing to be neglected when there is a decrease in funding and staffing levels because they are out of sight and out of mind until a problem occurs.

In my opinion the biggest benefit of conducting a smoke testing program is the high visibility and learning opportunities of the staff by being out in the collection system for a few days.

The public, in general, has a preconceived notion that the wastewater treatment plant operators don’t do much. Make sure to seize the opportunities that will arise while conducting this testing to explain what you are doing. You will be surprised how grateful they are! Staff will also be provided a great chance to familiarize themselves with the design, function, location and condition of the collection system that they seldom have a chance to get out and work in.

Smoke testing is conducted by placing a blower over a centrally located manhole and forcing non-toxic smoke-filled air through a sewer line. Depending on the equipment being used the smoke will be generated by lighting a smoke bomb or utilizing liquid smoke. Using liquid smoke will generally cut your labor costs. The smoke under pressure will fill the main line plus any connections; then follows the path of the leak to the ground surface quickly revealing the source of inflow and infiltration. Only enough force to overcome atmospheric pressure is required.

After placing the blower and filling the lines with smoke, staff will have to perform a visual inspection of the area being tested. When using liquid smoke, you control the time you want it to run. Typically, you will leave the smoke run until the crew has had ample time to do a thorough inspection. A field crew should consist of a minimum of two people.

You should check all connected lines, including abandoned and supposedly disconnected service lines, don’t rush because minor leaks can easily be overlooked. It is important to carefully check around houses with close attention given to cleanouts and roof leaders. It is not uncommon to see smoke coming out of the grass, wooded areas, or cracks in the pavement. If smoke is found during the inspection it must be carefully recorded so that it can be corrected after the testing. Cameras make the job easier because a picture will help you relocate the problem after testing so that you can take corrective measures. It is also proof of the leak found.

Blocking off a sewer line should not be necessary except when isolation is important. As long as openings exist for the smoke to follow, smoke tests are effective, regardless of surface type, soil type and depth of the lines.