Stormwater Glossary


Best Management Practices (BMPs): Activities, practices, facilities, and/or procedures that, when implemented to their maximum efficiency will prevent or reduce pollutants in discharges.

Clean Water Act (CWA): The Federal water quality control law governing surface waters establishing water quality objectives, waste discharge standards, and the National Pollutant Discharge Elimination System permit process; also called the Federal Water Pollution Control Act. Check out EPA's website for a great overview.

Designated Uses (DUs): Uses that society, through state and federal governments, determines should be attained in the waterbody. Examples include warmwater aquatic ecosystems, public water supply, and recreational fishing. Different parts of the waterbody often have varied uses.

Effluent Guidelines: National standards for wastewater discharges to surface waters and publicly-owned treatment works (municipal sewage treatment plants). EPA issues effluent guidelines for categories of existing sources and new sources under Title III of the Clean Water Act. The standards are technology-based (i.e., they are based on the performance of treatment and control technologies); they are not based on risk or impacts upon receiving waters.

National Pollution Discharge Elimination System (NPDES): Point sources must obtain a discharge permit from the proper authority (usually a state, sometimes EPA, a tribe, or a territory). These permits do not simply say "no discharge," ather, they set limits on the amount of various pollutants that a source can discharge in a given time. 

Nonpoint Source (NPS) Pollution: Pollution that, unlike pollution from industrial and sewage treatment plants, comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and manmade pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water. Loadings of pollutants from NPS enter waterbodies via sheet flow, rather than through a pipe, ditch or other conveyance.

Point Source of Pollution: Discrete conveyances, such as pipes or man made ditches that discharge pollutants into waters of the United States. This includes not only discharges from municipal sewage plants and industrial facilities, but also collected storm drainage from larger urban areas, certain animal feedlots and fish farms, some types of ships, tank trucks, offshore oil platforms, and collected runoff from many construction sites.

Publicly Owned Treatment Works (POTW): A treatment works as defined by Section 212 of the CWA, which is owned by the state or municipality). This definition includes any devices or systems used in the storage, treatment, recycling, and reclamation of municipal sewage or industrial wastes of a liquid nature. It also includes sewers, pipes or other conveyances only if they convey wastewater to a POTW treatment plant.

Regional Water Quality Control Board (RWQCB): Local Division of the State Water Resources Control Board. The RWQCB is charged with enforcement of the federal Clean Water Act, state and local legislation. There are nine regional quality control boards statewide.

Storm Drains: A system of gutters, catch basins, and over- and underground channels which carry runoff from city streets to the ocean. Storm drains can carry a variety of substances such as sediments, fecal waste, metals, bacteria, oil, and antifreeze which enter the system through runoff, deliberate dumping, or spills.

State Water Resources Control Board (SWRCB): The board was created by the State Legislature in 1967 and is comprised of five members. The goals of the Board are 1) protect water quality by setting statewide policy 2) coordinate and support Regional Water Board efforts 3) review petitions that contest Regional Board actions 4) allocate surface water rights.

Stormwater Pollution Prevention Plan (SPPP): A Storm Water Pollution Prevention Plan (SWPPP) must include a site description, including a map that identifies sources of storm water discharges on the site, anticipated drainage patterns after major grading, areas where major structural and nonstructural measures will be employed, surface waters, including wetlands, and locations of discharge points to surface waters

Total Maximum Daily Load (TMDL): A calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, a “pollutant budget.”  Required only for waterbodies that are considered “impaired.”

Water Quality Criteria: Levels of individual pollutants or water quality characteristics, or descriptions of conditions of a waterbody that, if met, will generally protect the designated use of the water.

Water Quality Standards (WQS): These standards aim to translate the goals of the Clean Water Act into measurable objectives.  Includes three major components: designated uses, water quality criteria, and antidegradation provisions.

Waters of the United States: As defined in the CWA, "waters of the United States" applies only to surface waters, rivers, lakes, estuaries, coastal waters, and wetlands. Not all surface waters are legally "waters of the United States." Generally, those waters include the following:

  • All interstate waters
  • Intrastate waters used in interstate and/or foreign commerce
  • Tributaries of the above
  • Territorial seas at the cyclical high tide mark; and
  • Wetlands adjacent to all the above

Watershed: A drainage area or basin in which all land and water areas drain or flow toward a central collector such as a stream, river, or lake at a lower elevation.