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Custer Avenue CSO Project Glossary

Connecting Tunnels – Tunnels that extend from the intake structures to the main tunnel. These tunnels are located at Shadowlawn, Roswell Road and Johnson Ferry Road. They total 2,332 feet in length and will be excavated by drilling and blasting. These sections of tunnel will be lined with pre-cast concrete pipe.

Continuous Conveyor – The system of rock removal from the tunnel, whereby a continuous conveyor system in used to transport rock cuttings (tunnel muck) from the TBM to the muckpile located at the ground surface adjacent to the construction shaft. The conveyor system includes a series of transfer conveyors as well as a vertical belt at the shaft.

Intake – Structures used to transfer flow from the truck sewers down to the tunnel. On the Nancy Creek Tunnel, eight intakes will be constructed. The intakes include a tangential vortex drop structure, a drop and vent pipe. The drop and vent pipes will be installed using a technique called “raise boring.” The advantage of raise boring is that cuttings from the drilling operation drop back into the tunnel and are removed at the construction shafts, rather than at the intake locations.

Pump Station – The lift station located on the R.M. Clayton WRC site at the end of the tunnel to lift flow up to the treatment plant. The pump station will be constructed as a separate contract from the Nancy Creek Tunnel.

Tunnel – The horizontal excavation. On the Nancy Creek Tunnel, the main tunnel extends 43,700 feet from the Johnson Ferry Road shaft to the RM Clayton shaft. Along the alignment, the depth of the tunnel ranges from 95 to 330 feet. Only about 800 feet of the 43,700-foot length will be excavated by drilling and blasting (400 foot long TBM starter tunnels at the RM Clayton and Roswell Road shafts). The remaining length will be excavated using TBMs.

Tunnelling – Use of an underground tunnel to convey wastewater, storm water or combined flows to a treatment facility. Atlanta is already served by two wastewater tunnels - Three Rivers and Intrenchment Creek. A tunnel will be constructed in the Nancy Creek sewer basin to convey sanitary sewer flows from DeKalb to the R.M. Clayton WRC, providing relief from sewage overflows for northeast Atlanta residents.

TBM – Tunnel Boring Machines used to excavate hard rock tunnels. On the Nancy Creek Tunnel, there will be two electrically-powered, 18-foot diameter TBMs each equipped with thirty-nine - 19" disk cutters to cut the rock.

Shaft – The vertical excavation used to get from the ground surface down to tunnel grade. On the Nancy Creek Tunnel, 32- foot finished diameter construction shafts, varying in depth from 145 to 170 feet, are located at the R.M. Clayton WRC, Roswell Road and Johnson Ferry Road.

Basin – A segment or portion of a larger watershed area, based on the natural water drainage pattern.

Combined Sewer System – A one-pipe sewer system in which a single pipe collects both sewage and stormwater. In dry weather, all flow goes to a wastewater treatment plant. During wet weather, some flow may be diverted to CSO treatment facilities for storage and/or treatment. In heaviest rainfall, combined sewage flow may be discharged directly to streams.

Consent Decree – A negotiated agreement by the City to implement a court-ordered directive to evaluate and implement short and long-term plans for eliminating water quality violations. The City is currently operating under two consent decrees that resulted from lawsuits against the City, filed by the Upper Chattahoochee Riverkeeper, later joined by EPA and EPD. Two separate consent decrees address combined sewer overflows (CSO Consent Decree) and sanitary sewer overflows (First Amended (SSO) Consent Decree).

Combined Sewer Overflow (CSO) – Designed discharge from a combined sewer system into a stream. Usually occurs during heavy rainfall.

EPA – U.S. Environmental Protection Agency: The federal agency responsible for enforcing the Clean Water Act and other federal environmental regulations.

EPD – Georgia Environmental Protection Division: The Georgia agency responsible for enforcing EPA regulations as well as state environmental standards.

First Amended Consent Decree – A second Consent Decree agreement, signed in 1999, that addresses Sanitary Sewer Overflows (SSOs) and operation of the City’s wastewater treatment plants.

Impervious Surface – A surface that does not allow water or other liquids to pass through it (for example, pavement).

Separated Sewer System – A two-pipe sewer system in which one pipe collects sewage and sends it to a wastewater treatment plant and the other pipe collects storm water, which is typically discharged to a stream.

SSES – Sewer System Evaluation Survey (also Sanitary Sewer Evaluation Survey). A process of inspecting the inside of sewer pipes, using techniques such as Closed Circuit Television (CCTV), smoke testing, dye testing, flow monitoring and inspections to detect potential problems in sewer systems. The City’s SSES program, which began in June 2002, will address the entire system (2,200 miles) of pipe in the City.

SSO (Separate/Sanitary Sewer Overflow) – Sewage that flows out of a sanitary sewer pipe or overflow from a manhole onto the surface or into a stream. SSOs are a violation of the Clean Water Act.

SSO Remediation Deadline – All construction associated with meeting the terms of the First Amended Consent Decree (FACD) must be completed by July 2014. Failure to meet this deadline, and interim milestone deadlines in the FACD, will result in severe monetary penalties and a moratorium on development in the city.

Storm Water – Rainfall or other forms of precipitation. Storm water runoff is the result of storm water washing across impervious surfaces, carrying with it the pollutants found on streets, parking lots, rooftops, etc. These pollutants end up in streams and rivers. Storm water runoff contributes from 60 to 80% of total water pollution.

Wastewater – Water that has been discharged from homes and commercial and industrial establishments following use.

Watershed – The area of land that drains to a creek, stream or river.

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