BaySaver Stormwater Separation System Glossary


Best available technology economically achievable (applies to non-conventional and toxic pollutants)

A stormwater separation system designed to treat stormwater run-off.
When rain falls on an impervious surface, the runoff carries with it the oils, floatables (trash and debris) and sediments that have built up since the last storm.
The BaySaver Stormwater Separator System is designed to treat throughout an entire storm, not just the first flush.
To treat the entire storm, the BaySaver Separation System matches the treatment flow rate and path to the incoming flow rate. During the first flush, the BaySaver treats the entire volume of influent water through both manholes in series. As flow rates increase, the BaySaver enters into maximum treatment flow. During this phase, the BaySaver diverts water containing free oils, fine sediments, and floatables, to the storage manhole for secondary treatment while the primary manhole treats and cleans the remaining flow. During peak design flow, gravity removes large suspended solids in the primary manhole. A portion of the flow passes through the storage manhole for further treatment. Portions in both manholes pass straight through the system thus avoiding resuspension of materials previously collected. This direct flow path for a portion of the water assures that the BaySaver will not back up the overall piping system.

Best conventional pollutant control technology (applies to conventional pollutants)

Best available technology / Best control technology
A level of technology based on the very best (state-of-the-art) control and treatment measures that have been developed or are capable of being developed and that are economically achievable within the appropriate industrial category

Best management practices
Activities or structural improvements that help reduce the quantity and improve the quality of stormwater runoff. BMPs include treatment requirements, operating procedures, and practices to control site runoff, spillage or leaks, sludge or waste disposal, or drainage from raw material storage.

Dense vegetation designed to filter stormwater runoff as it passes through

Best management practice

Buffer strip or buffer zone
Strip of grass or other erosion-resistant vegetation located between a waterway and an area of more intensive land use

Catch basin
An entryway to the storm drain system, usually located at a street comer. See Baysaver.

Category (XI) facilities
Specific facilities classified as light industry with equipment or materials exposed to stormwater

Code of Federal Regulations

Clean Water Act
Legislation that provides statutory authority for the NPDES program; Public law 92-500; 33 U.S.C. 1251 et seq. Also known as the Federal Water Pollution Control Act.

Coastal Zone Act Reauthorization Amendments (CZARA)
The Coastal Nonpoint Source Pollution Control Program (Section 6217) addresses nonpoint pollution problems in coastal waters. Section 6217 requires the 29 states and territories with approved Coastal Zone Management Programs to develop Coastal Nonpoint Pollution Control Programs. In its program, a state or territory describes how it will implement nonpoint source pollution controls, known as management measures, that conform with those described in Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters (available at This program is administered jointly with the National Oceanic and Atmospheric Administration (NOAA).

Code of Federal Regulations
The compilation of federal regulations. Each area of regulation is contained in a separate volume (e.g., environmental regulations are compiled in volume 40, or 40 CFR). Each volume contains up to several hundred parts.

Any channel or pipe used to transport flowing water

The process of water moving from one place to another

Combined sewer overflow

A short, closed (covered) conduit that passes stormwater runoff under an embankment, usually a roadway. A rectangular or square concrete culvert is referred to as a box culvert.

A stormwater system that delays the downstream progress of stormwater runoff in a controlled manner, typically by using temporary storage areas and a metered outlet device See Baysaver.

Also levee; an embankment used to confine or control water. Dikes are often built along the banks of a river to prevent overflow.

The volume of water (and suspended sediment if surface water) that passes a given location within a given period of time

Drain inlet insert
A device (tray, bag, or basket) installed in a drain inlet or catch basin to treat stormwater runoff

Removal of soil particles by wind and water. Often the eroded debris (silt or sediment) becomes a pollutant via stormwater runoff. Erosion occurs naturally but can be intensified by human activities such as farming, development, road-building, and timber harvesting.

The process of removing earth, stone, or other materials from land
A temporary rise in flow or stage of any watercourse or stormwater conveyance system that results in stormwater runoff exceeding its normal flow boundaries and inundating adjacent, normally dry areas

Flood control
The specific regulations and practices that reduce or prevent the damage caused by stormwater runoff
General permit
A permit issued under the NPDES program to cover a certain class or category of stormwater discharges. These permits reduce the administrative burden of permitting stormwater discharges.

The cutting and/or filling of the land surface to a desired slope or elevation
Holding pond
A pond or reservoir, usually made of earth, built to store polluted runoff for a limited time

Illicit connection
Any discharge to a municipal separate storm sewer that is not composed entirely of stormwater and is not authorized by an NPDES permit, with some exceptions (e.g., discharges due to fire-fighting activities)

International Erosion Control Association

Impermeable material
A soil or material whose properties prevent movement of water through the material

Impervious surface
Hard ground cover that prevents or retards the entry of water into the soil and increases runoff, such as asphalt, concrete, rooftops

Industrial activity
Any activity directly related to manufacturing, processing, or raw materials storage areas at an industrial plant

The portion of rainfall or surface runoff that moves downward into the subsurface rock and soil
Large municipal separate storm sewer system (MS4)
An MS4 located in an incorporated place or county with a population of 250,000 or more, as determined by the 1990 U.S. Census

Light manufacturing facilities
Described under Category (XI) of the definition of "stormwater discharges associated with industrial activity" [40 CFR 122.26(b)(14)(XI)]. Under the Phase I NPDES program, these facilities were eligible for exemption from stormwater permitting requirements if certain areas and activities were not exposed to stormwater. As a result of the Phase II Final Rule, these facilities must now certify to a condition of no exposure.
Maximum extent practicable (MEP)
A standard for water quality that applies to all MS4 operators regulated under the NPDES program. Since no precise definition of MEP exists, it allows for maximum flexibility on the part of MS4 operators as they develop and implement their programs.

Media filter
A filter containing sand, compost, sand peat, or perlite and zeolite designed to filter constituents (particulates, oil, bacteria, or dissolved metals) out of stormwater runoff as it passes through the filter

Medium municipal separate storm sewer system (MS4)
MS4 located in an incorporated place or county with a population of 100,000 or more but less than 250,000, as determined by the 1990 U.S. Census

Maximum extent practicable

Municipal separate storm sewer system
Municipal separate storm sewer system (MS4)
A publicly owned conveyance or system of conveyances that discharges to waters of the US and is designed or used for collecting or conveying stormwater, is not a combined sewer, and is not part of a publicly owned treatment works (POTW)

Multisector general permit (MSGP)
An NPDES permit that regulates stormwater discharges from 11 categories of industrial activities
National Pollutant Discharge Elimination System
Two-phased surface water quality program authorized by Congress as part of the 1987 Clean Water Act

"No exposure"
Protection of all industrial materials or activities by a storm-resistant shelter to prevent exposure to rain, snow, snowmelt, and/or runoff.

Non-delegated state
Any state that does not have the authority to implement the NPDES stormwater program

Nonpoint-source pollutants
Pollutants from many diffuse sources. Nonpoint-source 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 human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even underground sources of drinking water.

Notice of Intent (NOI)
An application to notify the permitting authority of a facility;s intention to be covered by a general permit; exempts a facility from having to submit an individual or group application

National Pollutant Discharge Elimination System, the two-phased surface water quality program authorized by Congress as part of the 1987 Clean Water Act
The point where wastewater or drainage discharges from a sewer pipe, ditch, or other conveyance to a receiving body of water
Permitting authority
The NPDES-authorized state agency or EPA regional office that administers the NPDES program, issuing permits, providing compliance assistance, conducting inspections, and enforcing the program

Physically interconnected MS4
One MS4 connected to a second MS4 in such a way that allows direct discharges into the second system

Point-source pollutants
Pollutants from a single, identifiable source such as a factory or refinery; also called single-point-source pollution

Pollutant loading
The total quantity of pollutants in stormwater runoff
Regulated MS4
Any MS4 covered by the NPDES program (regulated small, medium, or large MS4s)

The modification of stormwater management systems through the construction and/or enhancement of wet ponds, wetland plantings, or other BMPs designed to improve water quality

Drainage or flood discharge that leaves an area as surface flow or as pipeline flow

Sanitary sewer
A system of underground pipes that carries sanitary waste or process wastewater to a treatment plant

Section 319 grant
A grant, under section 319 of the Clean Water Act, that pays up to 60% of the cost of a project to prevent or control nonpoint source pollution

Soil, sand, and minerals washed from land into water, usually after rain. Sediment can destroy fish-nesting areas, clog animal habitats, and cloud waters so that sunlight does not reach aquatic plants.

A device for separating liquids of differentspecific gravities (as oil from water) or liquids from solids.

Sheet flow
The portion of precipitation that moves initially as overland flow in very shallow depths before eventually reaching a stream channel

Site runoff
Any drainage or flood discharge that is released from a specified area

Small municipal separate storm sewer system (MS4)
Any MS4 that is not regulated under Phase I of the NPDES program

State revolving fund loan
Low-interest loan to pay for infrastructure investments such as wastewater treatment facilities, landfill closures, and habitat restoration. Federal and state funding provide the seed money, and repayment of earlier loans keeps the system going.

Storm drain
An opening leading to an underground pipe or open ditch for carrying surface runoff, separate from the sanitary sewer or wastewater system

Storm surge
An increase in water level above the normal water level on the open coast due to the action of wind stress and atmospheric pressure on the sea surface

Precipitation that accumulates in natural and/or constructed storage and stormwater systems during and immediately following a storm event

Stormwater management
Functions associated with planning, designing, constructing, maintaining, financing, and regulating the facilities (both constructed and natural) that collect, store, control, and/or convey stormwater

Stormwater pollution prevention plan (SWPPP)
A plan to describe a process though which a facility thoroughly evaluates potential pollutant sources at a site and selects and implements appropriate measures designed to prevent or control the discharge of pollutants in stormwater runoff

Stormwater utility
Special assessment district set up to generate a stable source of funding for stormwater management within a region, usually through user fees

Surface runoff
The portion of rainfall that moves over the ground toward a lower elevation and does not infiltrate the soil

Surface water
Water that remains on the surface of the ground, including rivers, lakes, reservoirs, streams, wetlands, impoundments, seas, and estuaries

Stormwater management plan (or program)
Total maximum daily load (TMDL)
The maximum allowable loading of a pollutant that a designated water body can assimilate and still meet numeric and narrative water quality standards. TMDLs were established by the 1972 Clean Water Act. Section 303(d) of the US Water Quality Act requires states to identify water bodies that do not meet federal water quality standards. In 1996 the states developed (with EPA approval) a list of water bodies that failed to meet section 303(d) standards. These are the focus of TMDLs. Allocation of named pollutants is on percentage basis.

Tool box
A term to describe the activities and materials that EPA plans to perform/produce to facilitate implementation of the stormwater program in an effective and cost-efficient manner. The eight components include fact sheets, guidance documents, menu of BMPs, compliance assistance, information clearinghouse, training and outreach efforts, technical research, and support for demonstration projects.
Urbanized area
A Bureau of the Census determination of a central place (or places) and the adjacent densely settled surrounding territory that together have a minimum residential population of 50,000 people and a minimum average density of 1,000 people/mi.2

Urban runoff
Stormwater from urban areas, which tends to contain heavy concentrations of pollutants from urban activities
Geographical area that drains to a specified point on a water course, usually a confluence of streams or rivers. Also known as drainage area, catchment, or river basin. (In the UK the term "watershed" refers to what in the US is called the drainage divide, and the term "catchment" refers to what in the US is called a watershed.)

Wet weather flows
Water entering storm drains during rainstorms/wet weather events

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