Glossary terms obtained from Long Term Control Plan.

Adaptive Management Approach – As defined by the EPA, is “the process by which new information about the health of a watershed is incorporated into the watershed management plan.” The City has applied this process to the CSO Long Term Control Plan and implementation of individual controls by continually evaluating existing controls, identifying new controls, and determining the most cost-effective way to achieve water quality objectives.

Best Management Practice – These are stormwater treatment methods that have been determined to be the most effective, practical means of preventing or reducing pollution.

Biochemical Oxygen Demand (BOD) – A measure of the amount of oxygen consumed in the biological processes that break down organic matter in water. The greater the biochemical oxygen demand, the greater the degree of pollution.

Capture (Percent Capture) – The percentage by volume of combined sewer flow in the combined sewer system that receives treatment or is otherwise controlled.

Clean Water Act – An act passed by the US Congress to control water pollution. The Federal Water Pollution Control Act passed in 1972 (Public Law [PL] 92-500). It was amended in 1977 (the Clean Water Act, PL 95-217) and again in 1987 (the Water Quality Act, PL 100-4).

Combined Sewer Overflow (CSO) – Discharge of a mixture of stormwater and domestic/industrial/commercial wastewater. The overflow occurs when the flow capacity of a combined sewer system is exceeded during a rain event.

CSO Control Policy – EPA’s CSO Control Policy is a national framework for control of CSOs through the National Pollutant Discharge Elimination System (NPDES) permitting program. The Policy resulted from work with municipal organizations, environmental groups and state agencies. It provides guidance to municipalities and permitting authorities on flexible, cost-effective ways communities can meet Clean Water Act pollution control goals (

The Policy has since been incorporated into the Clean Water Act through the Wet Weather Water Quality Act of 2000.

Combined Sewer System (CSS) – A sewer system that carries both sewage and stormwater. Normally, the entire flow goes to a water resource recovery facility, but during a heavy flows, the volume of water may be so great as to cause overflows of untreated mixtures of stormwater and sewage into receiving waters.

Combined Sewer System Model (CSS Model) – A comprehensive model, organized into three model elements: hydrologic runoff to simulate wet weather flow, dry-weather flow to simulate sanitary flows, and the hydraulic collection system to simulate the separated and combined sewer systems.

Community Enhancements – Efforts of the City of Omaha or a neighborhood to implement positive green and/or aesthetic enhancements during planning and construction of a CSO Project. Enhancements include tree planting and landscaping, installing or replacing sidewalks, and incorporating public art.

Deactivated CSO – A combined sewer overflow location which no longer discharges untreated water.

Detention – The delay or holding of the flow of water in a pipe system. This can be caused by a restriction in the pipe, a stoppage, or a dip. Detention also refers to the time water is held or stored in a basin or a wet well.

Dewater – The draining or removal of water or sewerage from a tank or retention treatment basin (RTB).

Disinfection – The process designed to kill or inactivate most microorganisms in water or wastewater, including essentially all disease-causing bacteria. There are several ways to disinfect, with chlorination being the most frequently used in water and water resource recovery facilities.

Dissolved Oxygen – The oxygen freely available in water, vital to fish and other aquatic life and for the prevention of odors. Dissolved oxygen levels are considered the most important indicator of a water body’s ability to support desirable aquatic life. Secondary and advanced waste treatments are generally designed to ensure adequate dissolved oxygen in waste receiving waters.

Diversion Structure (Chamber) – A chamber or box that contains a structure for diverting or drawing off all or part of a flow for discharge to various outlets.

Drop Shaft – A vertical opening used to provide access to a tunnel.

Escherichia coli (E. coli) – One of the species of bacteria in the fecal coliform group. It is found in large numbers in the gastrointestinal tract and feces of warm-blooded animals and humans. Its presence is considered indicative of fresh fecal contamination, and it is used as an indicator organism for the presence of less easily detected pathogenic bacteria.

Existing Conditions – The combined sewer system as it was in the year 2002, which is the year the City of Omaha’s first CSO National Pollutant Discharge Elimination System permit was issued by the Nebraska Department of Environment and Energy.

Floatables Control – Technologies designed to reduce or eliminate the visible solid waste that is often present in CSO discharges.

Force Main – A pressure pipe joining the pump discharge at a water or wastewater pumping station with a point of gravity flow.

Full Sewer Separation – Public and private sewer separation.

Gravity Flow (Sewer) – Water or wastewater flowing from a higher elevation to a lower elevation due to the force of gravity. In this scenario, water does not flow due to energy provided by a pump. Wherever possible, wastewater collection systems are designed to use the force of gravity to carry waste liquids and solids.

Green Infrastructure – Green infrastructure uses natural or engineered systems designed to mimic natural processes to manage urban stormwater and reduce impacts. These systems are often soil or vegetation based and include approaches such as tree preservation and impervious cover (like concrete) reduction, as well as structural interventions like rain gardens and permeable pavements (like pavers). By maintaining or restoring the hydrologic function of urban areas, green infrastructure treats precipitation as a resource rather than waste, and can play a critical role in achieving community development as well as water quality goals.

Grit Removal – Grit removal is accomplished by providing an enlarged channel or chamber that causes flow velocity to be reduced and allows the heavier grit to settle to the bottom of the channel where it can be removed.

Groundwater Infiltration – The quantity of groundwater that leaks into a pipe through joints, porous walls, or breaks.

Headworks – Initial structures and devices of a water or water resource recovery facility.

High-Rate Treatment – Treatment processes intended to provide a treatment level equivalent to primary treatment, as required by U.S. Environmental Protection Agency’s CSO Control Policy, plus disinfection to achieve an effluent quality of 126 E. coli organisms per 100 milliliters. Alternative high-rate treatment processes are sand ballasted sedimentation or retention treatment basins.

Lift Station – A structure that contains pumps, piping, valves, and other mechanical and electrical equipment for pumping water, wastewater, or other liquid. Also called a pumping station.

Major Projects – Facility projects and sewer separation projects linked to these facility projects identified in the Long Term Control Plan.

Missouri River Watershed – The watershed that includes study basins where combined sewage flows through sewers and is ultimately pumped to the Missouri River Water Resource Recovery Facility.

National Pollutant Discharge Elimination System (NPDES) Permit – The regulatory agency document issued by either a federal or state agency that is designed to control all discharges of potential pollutants from point sources and stormwater runoff into US waterways. NPDES permits regulate discharge into US waterways from all point sources of pollution, including industries, municipal water resource recovery facilitys, sanitary landfills, large animal feedlots, and return irrigation flows.

Nine Minimum Controls – Includes minimum technology based controls that can be used without extensive engineering studies or significant construction costs, prior to implementation of long-term controls.

Papillion Creek Watershed – The watershed that includes those study basins with combined sewers that flow into the Papillion Creek Interceptor and to the Papillion Creek Water Resource Recovery Facility.

Preliminary Treatment – Unit operations, such as screening and grit removal, that prepare wastewater for subsequent major treatment.

Presumption Control Level (Approach) – An approach that meets criteria as defined by the U.S. Environmental Protection Agency CSO Control Policy. The presumption approach requires either the capture of at least 85 percent by volume, annually, of the combined sewage entering the collection system during wet weather, or no more than four to six untreated overflows during an average year.

Primary Treatment – The first major treatment in a wastewater treatment facility, used for the purpose of sedimentation. Wastewater treatment processes usually consist of clarification with or without chemical treatment to accomplish solid–liquid separation.

Private Sewer Separation – Elimination of inflow sources on private property.

Program – The effort to implement the Long Term Control Plan for the City of Omaha.

Program Management Team – Members of the City of Omaha, CH2M HILL, HDR Inc., and Lamp Rynearson & Associates, Inc. who are working on the CSO Program.

Public Sewer Separation – Separation of sewers within public rights of way, not including the elimination of inflow sources on private property.

Representative Year – The year (1969) selected for the development of baseline CSO hydrographs for evaluating CSO controls, based on statistical analysis of historic precipitation data from Eppley Airfield.

Retention Treatment Basins – Large settling basins to which chemicals are added for disinfection and de–chlorination. During smaller wet weather events, the entire CSO volume will be captured and pumped out to an existing water resource recovery facility. During larger events, basins will discharge treated water to a receiving stream.

Sanitary Sewer – A sewer that carries only liquid and waterborne wastes from residences, commercial buildings, industrial plants, and institutions together with minor quantities of ground, storm, and surface water that are not admitted intentionally to a water resource recovery facility for treatment.

Screen – A device with openings, generally of uniform size, used to retain or remove suspended or floating solids preventing them from passing a given point in a conduit. The screening element may consist of parallel bars, rods, wires, grating, wire mesh, or perforated plate.

Secondary Treatment – Commonly applied to treatment that consists chiefly of clarification followed by a biological process with separate sludge collection and handling.

Storm Sewer – A sewer that carries only storm water flows.

Stormwater Runoff – Water flowing over land during and immediately following a rainstorm or snowmelt. Stormwater carries nutrient laden sediment, heavy metals, oils, and other materials that have accumulated on the land between rain events and carries them into streams, rivers, and lakes.

Sustainability – The three primary components of sustainability as they relate to CSO Program goals are economic growth, environmental stewardship, and social progress.

Total Maximum Daily Load – A Total Maximum Daily Load (or TMDL) is a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards, and an allocation of that amount to the pollutant’s sources.

Total Suspended Solids – A measure of suspended solids in wastewater, effluent, or water bodies, determined by tests for “total suspended non-filterable solids”.

Watershed – The region or land area that contributes to the drainage or catchment area above a specific point on a stream or river.

Wet Well – A compartment or tank in which wastewater is collected. The suction pipe of a pump may be connected to the wet well or a submersible pump may be located in the wet well.