Stormwater Terms

HRT

Hydraulic residence time

MS4

Municipal Separate Storm Sewer System

SWMP

Stormwater Management Program

Eutrophic

A condition of a water body in which excess nutrients, particularly phosphorous, stimulates the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen. Thus, less dissolved oxygen is available to other aquatic life.

Drainage facility

A constructed or engineered feature that collects, conveys, stores or treats surface and storm water runoff. Drainage facilities shall include but not be limited to all constructed or engineered streams, pipelines, channels, ditches, gutters, lakes, wetlands, closed depressions, flow control or water quality treatment facilities, erosion and sedimentation control facilities, and other drainage structures and appurtenances that provide for drainage.

Flow Restrictor sketch

A control device or a T section with a specifically sized orifice(s) to control release rates.

Buffer

A designated area adjacent to and a part of a steep slope or landslide hazard area which protects slope stability, attenuation of surface water flows, and landslide hazards reasonably necessary to minimize risk; or a designated area adjacent to or a part of a stream or wetland that is an integral part of the stream or wetland ecosystem.

Catch basin insert

A device installed underneath a catch basin inlet to treat stormwater through filtration, settling, absorption, adsorption, or a combination of these mechanisms. There are a number of shapes, sizes, and configurations of inserts available.

Flow control facility

A drainage facility designed to mitigate the impacts of increased surface and storm water runoff generated by site development pursuant to the drainage requirements in King County Code Chapter 9.04. Flow control facilities are designed either to hold water for a considerable length of time and then release it by evaporation, plant transpiration, and/or infiltration into the ground, or to hold runoff a short period of time and then release it to the conveyance system.

Detention facility

A facility that collects water from developed areas and releases it at a slower rate than it enters the collection system. The excess of inflow over outflow is temporarily stored in a pond or a vault and is typically released over a few hours or a few days. Detention Pond Detention Tank Detention Vault

303(d) waterbody

A list of lakes, rivers, and streams that have been designated as impaired or threatened by a pollutant(s) for which one or more TMDL(s) are needed. Impaired means that the water is not meeting state water quality standards

Biofiltration swale or Bioswale sketch

A long, gently sloped, vegetated ditch designed to filter pollutants from stormwater. Grass is the most common vegetation, but wetland vegetation can be used if the soil is saturated.

Pollution-generating pervious surface

A non-impervious surface with vegetative ground cover subject to use of pesticides and fertilizers. Such surfaces include, but are not limited to, the lawn and landscaped areas of residential or commercial sites, golf courses, parks, and sports fields.

Basin plan

A plan and all implementing regulations and procedures including but not limited to capital projects, public education activities, land use management regulations adopted by ordinance for managing surface and storm water management facilities, and features within individual subbasins.

Catch Basin, Type II

A round concrete underground basin (4'-8' diameter; 6' or greater deep); may contain Flow Restrictor/Oil Pollution control device. These basins are also required when larger diameter culverts are used. Also referred to as a Manhole or Control Manhole.

Small MS4s

A small MS4 is defined as any MS4 that is not a medium or large MS4 covered by Phase I of the NPDES Storm Water Program. Only some small MS4s are regulated. See EPA information on regulatory applicability.

Compliance with TMDLs in Idaho

A total maximum daily load (TMDL) is a water quality improvement plan that provides a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards. TMDLs are calculated for surface water bodies that do not meet water quality standards; their purpose is to improve poor water quality. Since stormwater can discharge pollutants to streams, lakes, and rivers, stormwater discharges must be consistent with the requirements of a TMDL that has been developed for a particular water body. If a TMDL has been established for the stream, lake, or river where stormwater will discharge, the stormwater discharger should contact DEQ to determine if there are specific TMDL stormwater requirements. Following BMPs from the Catalog of Stormwater Best Management Practices for Idaho Cities and Counties described below is generally sufficient to meet TMDL requirements, but it is best to discuss BMPs with DEQ before implementing if a TMDL is in place.

Critical Drainage Area

An area with such severe flooding, drainage, and/or erosion/sedimentation conditions which have resulted or will result from the cumulative impacts of development and urbanization, that the area has been formally adopted as a Critical Drainage Area by rule

Pollution-generating impervious surface

An impervious surface considered to be a significant source of pollutants in surface and storm water runoff.. Such surfaces include those subject to vehicular use or storage of erodible or leachable materials, wastes, or chemicals, and which receive direct rainfall or the run-on or blow-in of rainfall. Thus, a covered parking area would be included if runoff from uphill could regularly run through it or if rainfall could regularly blow in and wet the pavement surface. Metal roofs are also considered pollution-generating impervious surface unless they are treated to prevent leaching.

Catch Basin, Type I

An underground concrete water receiving inlet, rectangular in shape (approximately 3' x 2' x 4' deep) with a slotted iron grate on top to inlet water or a solid rectangular cover. Water may also enter/exit through culverts visible in the side walls of basin. Also referred to as Inlet.

Business, Industry, and Land Owners

Businesses, industry, and land owners are responsible for stormwater runoff from their property and may need to obtain a stormwater NPDES permit from EPA and/or comply with their city's municipal stormwater NPDES permit. Compliance with a stormwater permit may require the use of stormwater best management practices (BMPs); their use is recommended although not required.

CFR

Code of Federal Regulations

CSO

Combined Sewer Overflow

CSD

Community Services District

CAFO

Concentrated Animal Feeding Operation A point sourse Polution-

Structural BMP

Constructed facilities or measures to help protect receiving water quality and control stormwater quantity. Examples include storage, vegetation, infiltration, and filtration.

Illicit discharges

Discharges of non-stormwater to the storm drainage system. Examples are discharges from internal floor drains, appliances, industrial processes, sinks, and toilets that are connected to the nearby storm drainage system. These discharges should be going to the sanitary sewer system, a holding tank, an on-site process water treatment system, or a septic system.

Conveyance System

Drainage facilities and features that collect, contain, and provide for the flow of surface and storm water from the highest points on the land down to a receiving water. Conveyance systems are made up of natural elements and of constructed facilities.

NPDES permitting authority

EPA, Region 10, is the NPDES permitting authority for Idaho and is responsible for issuing NPDES stormwater permits.

EIS

Environmental Impact Statement. A document that discusses the likely significant adverse impacts of a proposal, ways to lessen the impacts, and alternatives to the proposal. It is required by the national and state environmental policy acts when projects are determined to have the potential for significant environmental impact.

ESC

Erosion and Sediment Control

FEMA

Federal Emergency Management Agency.

Constructed conveyance system facilities

Gutters, ditches, pipes, channels, and most flow control and water quality treatment facilities.

IWMA

Integrated Waste Management Authority

LID

Low Impact Development

Local Government

Many communities have stormwater NPDES permits and related stormwater ordinances that impact everyone, including individuals. Stormwater ordinances are designed to minimize the environmental threat to Idaho's rivers, lakes, and streams by prohibiting certain activities that would directly discharge into stormwater sewer systems. For more information about local ordinances in your community, contact your local public works department, highway district, or county.

MEP

Maximum Extent Practicable

Dry Season

May 1 to September 30.

NPDES

National Pollutant Discharge Elimination System

NSP

Nonpoint Source Pollution

NOI

Notice of Intent

Culvert

Pipe or concrete box structure which drains open channels, swales, or ditches under a roadway or embankment typically with no catch basins or manholes along its length.

Dispersed discharge

Release of surface and storm water runoff from a drainage facility system such that the flow spreads over a wide area and is located so as not to allow flow to concentrate anywhere upstream of a drainage channel with erodible underlying granular soils or the potential to flood downstream properties.

Detention

Release of surface and storm water runoff from the site at a slower rate than it is collected by the drainage facility system, the difference being held in temporary storage.

Discharge

Runoff, excluding offsite flows, leaving the proposed development through overland flow, built conveyance systems, or infiltration facilities.

SWRCB

State Water Resources Control Board

Point source pollutant

Storm water discharges are generated by runoff from land and impervious areas such as paved streets, parking lots, and building rooftops during rainfall and snow events that often contain pollutants in quantities that could adversely affect water quality. Most storm water discharges are considered point sources and require coverage by an NPDES permit. The primary method to control storm water discharges is through the use of best management practices.

SWPP2

Stormwater Pollution Prevention

SWPPP

Stormwater Pollution Prevention Plan

Stormwater

Stormwater is the water that runs off surfaces such as rooftops, paved streets, highways, and parking lots. It can also come from hard grassy surfaces like lawns, play fields, and from graveled roads and parking lots.

NPDES Permits?

The Clean Water Act prohibits anybody from discharging "pollutants" through a "point source" into a "water of the United States" unless they have an NPDES permit. The permit will contains: -limits on what you can discharge -monitoring and reporting requirements -provisions to ensure that the discharge does not hurt water quality or people's health. In essence, the permit translates general requirements of the Clean Water Act into specific provisions tailored to the operations of each person discharging pollutants.

Depression storage

The amount of precipitation that is trapped in depressions on the surface of the ground.

Erosion

The detachment and transport of soil or rock fragments by water, wind, ice, etc.

319

The section of the Federal Clean Water Act that deals with nonpoint pollution

Dead storage

The volume available in a depression in the ground below any conveyance system, or surface drainage pathway, or outlet invert elevation that could allow the discharge of surface and storm water runoff.

Determination of Non-Significance or DNS

The written decision by the responsible official of the lead agency that a proposal is not likely to have a significant adverse environmental impact per the SEPA process, and therefore an EIS is not required.

Direct discharge

Undetained discharge from a proposed project to a major receiving water.

UA

Urbanized Area

WDR

Waste Discharge Requirements

Idaho Department of Water Resources: IDWR

administers the Idaho waste disposal and injection well program and the stream channel alteration program. Injection wells can be used for stormwater runoff disposal; stream channel alteration permits are required when construction activities impact a stream below the mean high water mark. This includes constructing a stormwater outfall along a river, stream, or lake.

Treatment control measures

designed to remove pollutants after they have entered runoff. They tend to be more expensive than source control measures. An example of a treatment control is an oil/water separator.

Source control BMPs

focus on minimizing or eliminating the source of the pollution so that pollutants are prevented from contacting runoff or entering the drainage system.

Source control measures

focus on minimizing or eliminating the source of the pollution so that pollutants are prevented from contacting runoff or entering the drainage system. An example of a source control is maintaining existing vegetation in specific areas of a construction site to help control erosion.

Idaho Transportation Department: ITD

maintains the storm drain system that lies within the state highway right-of-way and incorporates erosion and sediment controls into its construction projects to keep sediment out of stormwater. The Idaho Transportation Department also periodically conducts erosion and sedimentation control workshops.

Idaho Department of Environmental Quality: IDEQ

provides technical assistance and support for controlling stormwater in Idaho. DEQ's Catalog of Stormwater Best Management Practices for Cities and Counties includes site-design techniques for controlling stormwater runoff associated with land development activities. DEQ also provides plan and specification review for facilities that control, treat, or dispose of stormwater if requested by the developer or design engineer.

Treatment control BMPs

tend to be more expensive to implement than source control BMPs, are designed to remove pollutants after they have entered runoff. Examples of source control BMPs include spill controls and employee education, while treatment control BMPs include detention ponds and oil/water separators. Most source control BMPs tend to be non-structural, and most treatment control BMPs tend to be structural in nature, although there can be exceptions. For example, a roof over a materials storage area at an industrial site would be considered a structural source control.