Smoke testing is an effective way to detect storm connections to the sanitary sewer. Roof drains and catch basins connected to the smoked line will emit smoke. If there are significant cracks or holes in the pipeline, the smoke will come up through the ground above the pipe. To detect this, the smoke testing must be done during dry weather periods.In smoke testing, a nontoxic smoke bomb is used to produce smoke. A blower (3500 CFM) is fitted over the top of the manhole for 15-20 minutes to purge the sewer of gases before the smoke is introduced. The pipes at the upstream and downstream manholes are blocked off to isolate a section of line. If there are any connections to the sewers, the smoke will travel up them. If there are any untrapped drains, the smoke will continue to travel until it gets to atmosphere.
Smoke testing is inexpensive. Sewer maintenance crews can easily carry it out. The engineer or technician in charge of the investigation should be on hand during the smoke test to observe and interpret the results. Pictures and videos should be taken to be included in the documentation. When planning smoke testing, allow for 5,000 to 7,000 feet of line per day to be tested with a crew of four men.
Always inform your customers through door hangers, bill inserts, newspapers, TV and/or radio before you start. Inform the fire department, police department, city hall and nearby building occupants when you will be performing the testing to prevent undue alarm. Expect frantic phone calls from people that think their house is on fire.
Dyed water testing is different from smoke testing in that dyed water is flooded on the surface or into potential sewer connections, and the nearest manhole is observed for signs of the dyed water. If the surface is flooded with dyed water and it gets into the pipe, it has entered through holes or cracks. If you suspect that a particular catch basin is connected to the sanitary sewer, you can dye running water from a hydrant or hose into the catch basin and look for it at the nearest downstream manhole. This is a very inexpensive technique and involves no equipment, just a bottle of dye and a water source. Dyeing is also a way to determine if an illegal drain is connected to the lines.
Smoke testing and dyeing are two inexpensive assessment tools to help determine where the inflow and infiltration you have in your system is coming from. They can also help to determine where you may be able to reduce inflow with little added expense by requiring the customer to remove the sources of inflow.