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CSO Glossary of Terms

Average dry weather flow (ADWF) – The average daily volume of flow entering the sewer system in dry weather.

Basement flood relief (BFR) – The minimum level of service for basement flood protection.

Best Management Practice (BMP) –  A practice or combination of practices that is determined to be an effective and practicable (including technological, economic, and regulatory considerations) means of preventing or reducing the amount of pollution generated from overflows to a level compatible with water quality goals.

Bio-retention / Rain garden – A depressed area of the ground planted with vegetation, allowing runoff from impervious surfaces (e.g., parking lots, roofs) to be collected, treated and filtered before being discharged downstream or returned to the atmosphere through evaporation and evapotranspiration.

Clean Environment Commission (CEC) – An arms-length provincial government agency designed to provide opportunities for the Manitoba public to play a part in ensuring the protection of our environment. This is done by providing a forum at which the public can participate in environmental assessment and decision-making, and in offering advice and recommendations to the government.

Combined sewer (CS) – A single pipe designed to carry two types of flow – wastewater (sewage from homes and businesses) and land drainage (rain and snowmelt). There are about 1,037 kilometres of combined sewers in Winnipeg. Typically, they serve areas of the city built before the 1960s.

Combined sewer overflow (CSO) – A discharge to the river when the capacity of a combined sewer is overwhelmed (e.g., during heavy rain or spring snowmelt). The discharge is a dilute mixture of wastewater (sewage from homes and businesses) and land drainage (rain or snowmelt).

Combined sewer districts – An area of the city served by a network of combined sewers. There are 43 combined sewer districts in Winnipeg.

Control limits – An established level of performance required through a regulatory licensing process. Maintaining levels within the acceptable control limit(s) ensures the required level of performance associated with regulatory licensing is met.

Dissolved oxygen (DO) – the amount of oxygen dissolved in liquid, expressed as milligrams per litre (mg/L) or percent saturation.

Downstream water quality – The condition of the water in our rivers when it flows out of Winnipeg.

Dry weather flow (DWF) – Flow entering sewers during dry weather from homes and businesses.

Escherichia coli (E. coli) – A large group of bacteria that normally live in the intestines of people and animals. Most E. coli are harmless and actually are an important part of a healthy human intestinal tract However, some strains can make people sick, causing severe stomach cramps, diarrhea and vomiting. Serious complications of an infection from a specific strain of E. coli can include kidney failure.

Event mean concentration (EMC) – A method for characterizing pollutant concentrations from a runoff event often chosen for its practicality. The value is determined by compositing (in proportion to flow rate) a set of samples, taken at various points in time during a runoff event, into a single sample for analysis.

Fecal coliform (FC) – Bacteria associated with fecal matter from humans and other warm blooded animals. Fecal coliform level is an indicator of pollution from raw sewage. Microbes in these wastes can cause short-term effects (e.g., diarrhea, cramps, nausea, headaches). They may pose a special health risk to infants, young children, some of the elderly, and people with severely compromised immune systems.

Floatables – Debris that floats in runoff, such as plastic, street litter (e.g., cigarette butts), and personal hygiene items (e.g., condoms, tampons).

Flood pump station (FPS) – Pumping stations dedicated to maintaining levels in the sewer system below basement flooding levels during wet weather events when the river levels are high. These stations pump wastewater to the rivers when gravity flow is not available due to system hydraulic constraints due to the high river levels.

Geographic Information System (GIS) – A database of digital information and data on land-use, land cover, ecology, and other geographic attributes that can be overlaid, statistically analyzed, mathematically manipulated, and graphically displayed using maps, charts and graphs.

Green infrastructure (GI) – Engineered, human-designed storm management systems that mimic nature by soaking up and storing rain water and snowmelt before it can reach the sewer system. Examples include:

  • green roofs, rain gardens,
  • permeable pavements, green alleys,
  • downspout disconnection (disconnecting a building’s roof drainage system from the combined sewer or land drainage system and redirecting the runoff from the roof onto permeable areas, such as lawns or gardens, or into rain barrels or cisterns to be stored and re-used)

Grey Infrastructure – Grey infrastructure refers to traditional human engineered solutions for stormwater management and wastewater treatment (e.g., pipes, sewers), versus green infrastructure that uses natural ecosystems to reduces pollutants from entering waterways.

Grey water – means untreated, used household water that does not contain human waste and does not come from a toilet or urinal. It includes water from:

  • appliances, such as dishwashers or washing machines; and
  • plumbing fixtures such as sinks, bathtubs and showers.

Infiltration and Inflow
Infiltration is:

  • groundwater that infiltrates a sewer system through defective pipes, pipe joints, connections, or manholes,
  • generally measured during seasonally high ground water conditions, during dry weather.

Inflow is:

  • water other than sanitary flow that enters a sewer system from sources which include, but are not limited to, roof leaders, cellar drains, yard drains, area drains, drains from wet areas, cross connections between storm sewers and sanitary sewers, catch basins, cooling towers, stormwater, surface runoff (including leaking manhole covers), street wash-water, or drainage,
  • generally measured during wet weather.

Infiltration rate – The maximum velocity at which a soil can absorb water. It is usually measured by the depth (in mm) of the water that can enter the soil in one hour.

lnline storage – A control option for sewer overflows which involves storing wastewater in the sewers up to a level which does not increase the risk of basement flooding.

Land drainage sewers (LDS) – A system of single pipes designed to carry only rainfall and snowmelt directly to the river system. There are 1,326 kms of land drainage sewers in Winnipeg.

Life-Cycle Cost Analysis (LCCA) – A tool used to examine the environmental impacts and financial costs of a good or service, from its design through to production and then final disposal.

Manitoba Water Quality Standards, Objectives and Guidelines (MCWS, 2011) MWQSOG – Guide created by the provincial government to provide criteria for municipal wastewater effluents discharged to a water body.

Latent storage – The volume of collected runoff and wastewater that remains in the system after a runoff event. This volume cannot discharge to the rivers because the pipe, typically storm relief sewers, is lower than the river levels at the outfall location. This volume takes up space that could be used to collect runoff and reduce the CSO volume.

Environment Act Licence – Province of Manitoba Environment Act Licence No. 3042 issued to the City of Winnipeg on September 4, 2013, to regulate CSOs.

Low Impact Development (LID) – An approach to land development or redevelopment that works with nature to manage land drainage as close to its source as possible and includes a variety of practices that mimic or preserve natural drainage processes.

Nutrient – Element or compound essential for healthy animal and plant growth. Elevated concentrations of the nutrients, nitrogen and phosphorus, can degrade surface water quality, resulting in excessive, growth of algae and other nuisance aquatic plants.

Outfall – The final point of discharge into the river for the flow from a combined sewer, land drainage system or treatment plant effluent.

Overflow event – An event that occurs when there is one or more CSOs from a combined sewer system, resulting from rainfall or snowmelt.

Partially separated – An area of the city where part of the combined sewer system has been upgraded so that the wastewater and land drainage are carried separately.

Percent capture – the volume of wet weather flow treated in comparison to the volume of wet weather flow collected on a percentage basis over a given time frame.

Permeable (or porous) pavement – A special type of pavement that allows rain and snowmelt to seep into the ground rather than running off into storm drains and waterways. Well-maintained porous pavement filters pollutants from runoff before releasing it slowly to the surrounding soil.

Pollutant of Concern (POC) – a pollutant that is present in a discharge based on monitoring or is expected to be present in a discharge based on the source of the discharge that has the potential to adversely impact water quality or poses a health risk. POCs are typically linked to water quality standards.

Rainfall Derived Inflow and Infiltration (RDII) – the increased portion of water flow in a sewer system that occurs during and after a rainfall as a source of operating problems in the sewer system.

Real Time Control (RTC) – A system that dynamically adjusts the operation of facilities in response to online measurements in the field to maintain and meet the operational objectives, during both dry and wet weather conditions.

Recreation season – For purposes of analyzing surface water quality, the recreation season is usually May 1 to September 30.

Representative Year - A Representative Year is a record of actual rainfall at a single rain gauge for a whole year which statistically is considered to be representative of an average rainfall year. Part of the CSO Master Plan was to assess the long term rainfall record for the City of Winnipeg and determine a suitable Representative Year. Based on a review of the 60 years of historic rainfall data the 1992 year event was considered to be the representative Year.

The Representative Year allow designers and planners to size infrastructure to meet appropriate achievable levels of services and to management track progress over time.

Runoff – Water from rainfall, snowmelt, or other sources that flows over the ground surface, onto the street, through the storm drains at the curb and into the rivers.

Sanitary – Another engineering term for wastewater.

Sanitary Sewer Overflow (SSO) – Discharges of untreated sewage from municipal sanitary sewer systems as a result of broken pipes, equipment failure, or system overload.

Separate sewers – A system of two pipes where one pipe carries wastewater and the other carries land drainage (rain and snow melt). The role of the separate sewer system is to collect wastewater from homes and businesses and carry it to a sewage treatment plant. Since the 1960s, new property developments in the city have been serviced by this two-pipe system.

Stormwater retention basin (SRB) – Man-made ponds that store rainfall runoff from streets and adjacent lands. The ponds act as a natural filter by helping to remove sediment and chemicals before the water drains to our rivers.

Storm relief sewers (SRS) – A sewer designed to carry a portion of the land drainage flow from the combined sewer district where the existing sewers are of insufficient capacity. The combined sewer can surcharge and overflow into the SRS. The SRS conveys the additional flow directly to the rivers to help reduce the risk of basement flooding.

Stormwater – Another engineering term for wet weather flow (WWF).

Upstream water quality – The condition of the water in the rivers before it flows into the boundaries of Winnipeg.

Wastewater sewer overflow – Overflows to the rivers resulting from overloading of the wastewater sewers during high intensity storms. The main source of the high flow is interconnections of the wastewater and land drainage and storm relief sewers.

Wastewater sewers (WWS) – A system of single pipes that carry wastewater (sewage from homes and businesses) to sewage treatment plants.

Watershed – The land area, or catchment, that contributes water to a specific water body. All the rain or snow that falls within this area flows to the water bodies as surface runoff, in tributary streams, or as groundwater.

Weir – A dam built within a sewer pipe to contain and divert upstream flows. Weirs prevent dry weather overflows from occurring, but may allow overflows during surcharge conditions.

Wet weather period – Any period of precipitation (e.g., spring thaw) capable of contributing flow to a combined sewer system that exceeds the capability of the system to convey wet weather flows to a sewage treatment plant.

Sewage treatment plants – City-owned and operated facilities that receive the flow from wastewater and combined sewers, move the flow through a number of treatment processes, and then discharge the treated flow to the rivers. The plants operate under an Environment Act licence issued by the Province of Manitoba to protect public health and the freshwater environment. The licences set terms and conditions that the City is required to meet, including regularly monitoring plant operations and the quality of effluent discharged from the plants to the rivers. Three sewage treatment plants serve Winnipeg (north end, south end, west end). Wastewater from 90 percent of the combined sewer districts flows to the north end plant. Both the south end and west end plants collect sewage from three combined sewer districts each. All three plants treat flow from separate sewer areas.

Wet weather flow (WWF) – The combined amount of rainwater or snowmelt and wastewater that flows through the sewers in wet weather, not including average dry weather flow.

Last updated: April 15, 2024

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