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Glossary of Terms

Combined Sewer System

When domestic sewage combines with storm water in the same pipe. In the even of heavy rains, the storm water can cause an overflow (Combined Sewer Overflow or CSO) into a receiving stream or river.

Separate Sewer System

When domestic sewage and stormwater flow into separate pipes. The sewage is diverted to a wastewater treatment plant and storm water is released untreated to a receiving stream.

Open- Cut Construction

Involves digging down to the level of the existing pipe and replacing the old pipe with new pipe.


A process that uses a remotely controlled Microtunnel Boring Machine combined with the pipe jacking technique to directly install product pipelines underground in a single pass. This process avoids the need to have long stretches of open trench for pipe laying, which causes extreme disruption to the community.

Closed Circuit Television (CCTV)

CCTV technology uses a television camera mounted on a remotely controlled, self propelled robotic device that is connected to a video monitor, a videocassette recorder and other recording devices by a long electric cable to inspect sewer lines. The robotic system is placed directly into the sewer through a manhole. Once inside the sewer line, the remote-controlled device moves through the sewers and allows the operator to examine the entire length of pipeline between two manholes. The CCTV system relays live footage to a high resolution monitor located in a mobile survey unit. The footage of pipeline surveyed is recorded on videotape. If a defect is detected, the operator can stop the camera and investigate the defect in more detail.

Smoke Testing

A method used to locate sewers or test the pipe for cracks and breaks. It is conducted by placing a blower over a manhole and forcing non-toxic smoke-filled air through a sewer line. Under the pressure of the blower, the smoke will fill the sewer line plus any connections, then follow the path of any leaks to the ground’s surface, quickly revealing potential sources of inflow and infiltration.

Dye Testing

Dye testing with a non-toxic dye is used to confirm rain or ground entry points into the sanitary sewer system. Dyed water is introduced roof drain leaders, driveway drains, or area drains. In some instances, dyed water is injected into the ground around foundations to check for the illegal connections of foundation drains. After introducing the dyed water, the downstream sanitary sewer manhole is checked, and if a cleanout is present, it is checked for the presence of dyed water. Dye testing is one way of helping to determine where a pipe or structure drains if it is not obvious by observation or shown on existing plans records. Dye testing can help identify inappropriate connections.

Copyright 2003 City of Atlanta, Depart of Watershed Management. All rights reserved
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