Commonly Used Terms

Dry Weather Flow – Flow in a sanitary sewer during periods of dry weather in which the sanitary sewer is under minimum influence of inflow and infiltration.

Catch Basin – A chamber usually built at the curbline of a street, which conveys surface water for discharge into a storm sewer.

Collector Sewer – The first element of a wastewater collection system used to collect and carry wastewater from one or more building sewer laterals to a main sewer.

Combined Sewer System– Generally older sewer systems designed to convey both sewage and storm water into one pipe to a wastewater treatment plant.

Combined Sewer Overflow – The portion of flow from a combined sewer sytem, which discharges into a water body from an outfall located upstream of a wastewater treatment plant, usually during wet weather conditions.

Sanitary Sewer System – Wastewater collection system designed to carry sanitary sewage, consisting solely of domestic, commercial, and industrial wastewater. This type of system is not designed nor intended to carry water from rainfall, snowmelt, or groundwater sources.

Sanitary Sewer Overflow – Overflow from a sanitary sewer system caused when total wastewater flow exceeds the capacity of the system.

Infiltration – Water other than wastewater that enters a wastewater system and/or building laterals from the ground through such means as defective pipes, pipe joints, connections, or manholes. (Infiltration does not include inflow.)

Inflow – Water other than wastewater that enters a wastewater system and building sewer from sources such as roof leaders, cellar drains, yard drains, area drains, foundation drains, drains from springs and swampy areas, manhole covers, cross connections between storm drains and sanitary sewers, catch basins, cooling towers, stormwaters, surface runoff, street wash waters, or drainage. (Inflow does not include infiltration.)

Infiltration/Inflow (I/I) – The total quantity of water from both infiltration and inflow.

Overflow Rate – Flow release rate, generally expressed as gallons per day (gpd) or million gallons per day (MGD).

Peak Flow – The maximum flow that occurs over a specific length of time (e.g., daily, hourly, instantaneously).

Wastewater Fees – Fees assessed to residential, commercial, and industrial users based upon volume of water consumption and strength of pollutants discharged into the water.

Wet Weather Flow – Dry weather flow combined with stormwater introduced into a combined sewer system, and dry weather flow combined with infiltration/inflow into a separate sewer.