CSO Control Program --
Glossary of Terms The following is a list of definitions of terms about combined sewers and more generally about wastewater treatment. a-c | d-g | h-l | m-p | r-s | t-z Raw sewage
Untreated wastewater.  Regulator
A structure that controls the flow of wastewater from two or more input pipes (trunk lines) to a single output (usually a larger interceptor line). Regulators can be used to restrict or halt flow, thus causing wastewater to be stored in the conveyance system until it can be handled by the treatment plant.
Runoff
That part of precipitation, snow melt, or irrigation water that runs off of the land surface into streams or other surface water instead of infiltrating the land surface. Secondary treatment
Biochemical treatment of wastewater after the primary stage, using bacteria to consume the organic wastes. The secondary treatment step includes aeration, settling, disinfection and discharge through an outfall. Secondary treatment in conjunction with primary treatment removes about 85 to 90 percent of suspended solids in wastewater. Sediment
Once-suspended material which has settled to the bottom of a liquid, such as the sand and mud that make up much of the shorelines and bottom of Puget Sound. Sediment quality standards
Standards which identify chemical concentration and biological toxicity limits allowed in sediments which correspond to no observable acute or chronic adverse effects on biological resources and which do not pose a significant health threat to humans. Sedimentation tanks
Tanks or tunnels for holding wastewater where floating wastes are skimmed off and solids settle by gravity. Settled solids, called "sludge," are pumped out for further treatment. Sedimentation tanks are also referred to as clarifiers. Separation, total or partial
A method for controlling combined sewer overflow whereby the combined sewer is separated into both a sanitary sewer and a storm drain, as is the practice in new development. Separation may be total, in which case no stormwater is diverted to the sanitary sewer, or it may be partial, involving only the removal of runoff from streets and parking lots from the sanitary system. Setpoint
A defined indicator point in an electronic or mechanical control system where an action takes place. In a sewage conveyance system, a setpoint is generally the liquid level or flow rate which causes a valve to be opened or closed or a pump to be activated. Sewer
A channel or conduit that carries wastewater or stormwater runoff from the source to a treatment plant or receiving stream. Sanitary sewers carry household, industrial, and commercial wastewater. Storm sewers carry runoff from rain or snow. Combined sewers carry both kinds of water. Sewer system
Collectively, all of the property involved in the operation of a sewer utility. It includes land, wastewater pipes, pumping stations, treatment plants, and general property. It may also be called a sewerage or wastewater system. Side sewer
A privately owned and maintained sewer which connects the plumbing system of the building to the public sewer pipes. State Environmental Policy Act (SEPA)
A state law (Chapter 43.21C RCW) that requires state agencies and local governments to consider environmental impacts when making decisions about certain activities, such as development proposals over a certain size, and comprehensive plans. As part of this process, environmental impacts are documented and opportunities for public comment are provided. Storage
A method for controlling combined sewer overflows by storing the combined sewage until the rainstorm subsides, then releasing it back into the conveyance system to be treated at the usual treatment plant. Storm drain
A system of gutters, pipes, or ditches used to collect and carry stormwater from buildings or land surfaces to streams, lakes, or other receiving waters. In practice storm drains carry a variety of substances such as sediments, metals, bacteria, oil, and antifreeze which enter the system through runoff, deliberate dumping, or spills. This term also refers to the end of the pipe where the stormwater is discharged. Storm sewer
A system of pipes (separate from sanitary sewers) that carry only water runoff from building and land surfaces. Stormwater
Water that is generated by rainfall and is often routed into drain systems in order to prevent flooding. Suspended solids
Small particles of organic or inorganic materials that float on the surface of, or are suspended in, sewage or other liquids and which cloud the water. The term may include sand, mud, and clay particles as well as waste materials. Synthetic Unit Hydrograph
Estimates amount and pattern of rainwater due to a "unit" of rainfall flowing into the sewer system over a certain period of time. The pattern is than factored according to the amount of rainfall that actually fell for the time period. These individual patterns are then added for each time step to get the cumulative hydrograph from each basin. a-c | d-g | h-l | m-p | r-s | t-z |
