Raleigh, NC

Raleigh, NC

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City of Raleigh Public Utilities Department

KEY ENGINEERING TERMS



Air release manhole:
A manhole that houses an air relief valve. The valve and manhole are located at the highest points of the wastewater pressure lines, called force mains, and allow air to bleed off. This prevents air bubbles from forming and possibly blocking the flow of wastewater in the pipeline.


Blasting: The act of detonating an explosive. For utility construction, this typical involves drilling into rock beneath the ground surface, placing explosives in the void space created by the drilling, and detonating the explosives to fracture the rock so that it can be more easily excavated by mechanical equipment for installation of utilities in trenches.


Bore: To make a hole in a solid substance with a rotary cutting instrument to allow for a pipe to be inserted.


Capital Improvement Program (CIP): A plan adopted by a government agency that documents proposed improvements through a certain time period and includes associated costs for the improvements. A CIP is used for establishing annual budgets.


Drainage basin: A geographical area that drains into a creek, river, or reservoir.


Equalization basin: A reservoir or basin that contributes to flow equalization by temporarily storing wastewater until peak flows subside and a more normal flow to the downstream collection system or treatment facility can be obtained.


Environmental assessment (EA): A written document, prepared in accordance with state and/or federal guidelines under the Environment Protection Act, which addresses direct, secondary, and cumulative impacts of a proposed engineering project on the environment.


Flow equalization: The process of controlling and equalizing the rate at which wastewater flows through the collection system and into the treatment facility. Wastewater flow can vary widely during the day, and maintaining a steady, even flow helps optimize treatment processes and pipe sizes.


Force main: A pipe that uses pressure to transport wastewater from the pump station to a downstream collection system or a wastewater treatment facility.


Gravity sewer: A pipe that uses a declining grade to cause wastewater to flow downstream. It is the most common type of sewer line in existence. Raleigh’s wastewater collection system functions primarily by gravity.


I&I: Inflow and infiltration causes excess water to seep into a wastewater collection system and possibly create overflows.


Infiltration: Ground water that leaks into a wastewater collection system through old, cracked, or faulty sewer pipes.


Inflow: Water from heavy rains or melted snow and ice that directly enters through openings into the wastewater collection system. An example would be water entering the system through manhole covers that are submerged during rain events.


Interceptor: A large pipe that collects wastewater flow from other smaller wastewater pipelines and transports it further downstream.


Microtunneling: A method of tunneling beneath the ground surface utilizing a remote controlled Microtunnel Boring Machine (MTBM), where excavated material at the tunnel face is mixed with bentonite and other lubrication fluids to create a slurry.  Pressure at the cutting face is balanced with earth removal, groundwater head, and propulsion of the tunnel support without manned entry.  Excavated material which is captured in the slurry is pumped to the surface and separated.


Open Cut: Open-cut pipeline construction involves laying pipe into a trench cut into the ground from the surface.  Trenches are open to the sky at the ground surface, as opposed to a tunnel or horizontal mine shaft.  The work area is broken into manageable sections along the length of the route.  Crews ahead of the current pipe section being installed clear the terrain, while crews in the back of this section restore the area.  Open-cut pipeline installation typically takes place during normal working hours to avoid disruption in the evening.

Open cut construction generally consists of the following stages:
1.       Install trench shoring system (if required)
2.       Excavate trench
3.       Install pipe bedding
4.       Lower pipe into the trench
5.       Fuse pipe joints
6.       Test newly installed pipe
7.       Backfill and compact earth covering pipe
8.       Restore surface conditions


Pump station: A facility that pumps wastewater from an interceptor to the wastewater treatment facility or a downstream collection system. In Raleigh, 115 public pump stations keep wastewater flowing to four wastewater treatment facilities.


Preliminary Engineering Report (PER): A written document, typically prepared by a licensed engineer, that evaluates an infrastructure improvement need. A PER provides information about the existing infrastructure, current situation, future need, alternatives for meeting the future need, cost estimates to implement each alternative, and a final recommended alternative (plan) for addressing the need.


Sanitary sewer overflow (SSO): A situation in which wastewater is discharged into the environment before it reaches the wastewater treatment facility. The discharge usually occurs through manholes, plumbing fixtures or service cleanouts. In Raleigh, most SSOs are caused by grease and debris (rags, sticks, rocks, personal hygiene products, etc.) being flushed into the sewer sytem via private sewer services.


Sanitary sewer system: An underground system of pipes that commonly uses gravity to transport wastewater from homes and businesses to a treatment facility, where the water is treated and released into natural water bodies like lakes and streams.


Sewer manhole: A structure through which a person can gain access to the underground wastewater collection system. In paved areas, manholes are flush with the pavement. In unpaved areas, they are often located one or two feet above the ground and are sometimes higher due to flood plain conditions.


Storm sewer system: An underground system that collects rainwater, melted snow, and ice, and transports the water to natural waterways, where it is released.


Tunnel: To make or excavate an underground passageway to allow for the installation of a pipe. A tunnel is usually required due to the pipe size or if a bore cannot be made due to presence of rock.


Utility easement: Use of private property for the purpose of laying gas, electric, water, and sewer lines.


Wastewater: Water previously used by a municipality, industry, or agriculture that has suffered a loss of quality as a result of use.


Wastewater collection system: A system of pipes and pump stations connected by a series of sewer manholes that collects used water from kitchen sinks, bathtubs, toilets, washing machines, dishwashers, etc., in homes and businesses and transports it to a wastewater treatment facility. Raleigh’s wastewater collection system consists of approximately 2,300 miles of pipeline, ranging in diameter from six inches to six feet. Each day, an average of 42 million gallons of wastewater is transported through Raleigh’s wastewater collection system to the wastwater treatment facilities. The City established its first wastewater collection system in 1890.


Wastewater treatment facility: The facility at which physical, biological, and chemical processes are used to remove pollution from wastewater before it is discharged into a body of water. The City of Raleigh operates four wastewater treatment facilities.


Wet-weather flow: Any storm-generated flow, such as flow caused by heavy rains or melting snow and ice.

 
City of Raleigh Public Utilities Department