1 March 1997
10-4. SMOKE TESTING. The introduction of smoke under low pressure into a sealed off portion
of the sewer system is used to determine sources of inflow. This method is effective in
- Roof, basement, yard, area, and foundation drains
- Abandoned building sewers
- Faulty connections
- Illegal connections
- Cross-connections with storm sewers
- Structurally damaged manholes.
Shallow deteriorated joints and pipes may also be detected in porous soil.
10-5. PHYSICAL INSPECTIONS. A visual inspection of the system above ground is important
- Confirming maps
- Determining the structural condition of manholes, including rings, covers, cone and walls,
steps, bench, and inverts
- Detecting settling of manholes or backfill
- Detecting evidence of ponding or surcharging.
Personnel can also enter manholes and, using mirrors and bright sunlight or portable, high
candlepower lamps, look down sewer lines to detect displaced joints, sediments, blockages,
roots entering joints, collapsed lines, and uneven settling. The lines should be cleaned prior to
10-6. REMOTE INSPECTIONS. A closer inspection can be made using a closed circuit
television camera, an ultrawide angle lens, and a high resolution monitor. After the line has been
cleaned of debris and roots, the camera is pulled through the sewer between manholes using a
variable speed electric wrench. Plugs are used to cut off flows. Photographs can be made of
defects as well as a videotape.