Virginia Administrative Code › Title 9 - ENVIRONMENT › Agency 25 - STATE WATER CONTROL BOARD › Chapter 875 - VIRGINIA EROSION AND STORMWATER MANAGEMENT REGULATION › Part V - Criteria and Requirements for Regulated Land-Disturbing Activities › Article 4 - Water Quantity and Water Quality Technical Criteria for Grandfathered Projects and Time Limits of Applicability Projects › Section 9VAC25-875-670 - Definitions

Current through Register Vol. 40, No. 24, July 15, 2024
For the purposes of this article only, the following
						words and terms have the following meanings unless the context clearly
						indicates otherwise:
"Aquatic bench" means a 10-foot to 15-foot wide bench
						around the inside perimeter of a permanent pool that ranges in depth from zero
						to 12 inches. Vegetated with emergent plants, the bench augments pollutant
						removal, provides habitats, conceals trash and water level fluctuations, and
						enhances safety.
"Average land cover condition" means a measure of the
						average amount of impervious surfaces within a watershed, assumed to be 16% or
						a calculated watershed-specific value for the average land cover condition as
						approved by the Chesapeake Bay Local Assistance Board prior to September 13,
						2011.
"Bioretention basin" means a water quality BMP engineered
						to filter the water quality volume (i) through an engineered planting bed
						consisting of a vegetated surface layer (vegetation, mulch, ground cover),
						planting soil, and sand bed and (ii) into the in-situ material.
"Bioretention filter" means a bioretention basin with the
						addition of a sand filter collector pipe system beneath the planting
						bed.
"Constructed wetlands" means areas intentionally designed
						and created to emulate the water quality improvement function of wetlands for
						the primary purpose of removing pollutants from stormwater.
"Development" means a tract of land developed or to be
						developed as a unit under single ownership or unified control that is to be
						used for any business or industrial purpose or is to contain three or more
						residential dwelling units.
"Grassed swale" means an earthen conveyance system that
						is broad and shallow with erosion resistant grasses and check dams, engineered
						to remove pollutants from stormwater runoff by filtration through grass and
						infiltration into the soil.
"Infiltration facility" means a stormwater management
						facility that temporarily impounds runoff and discharges it via infiltration
						through the surrounding soil. While an infiltration facility may also be
						equipped with an outlet structure to discharge impounded runoff, such discharge
						is normally reserved for overflow and other emergency conditions. Since an
						infiltration facility impounds runoff only temporarily, it is normally dry
						during nonrainfall periods. Infiltration basin, infiltration trench,
						infiltration dry well, and porous pavement shall be considered infiltration
						facilities.
"Layout" means a conceptual drawing sufficient to provide
						for the specified stormwater management facilities required at the time of
						approval.
"Nonpoint source pollutant runoff load" or "pollutant
						discharge" means the average amount of a particular pollutant measured in
						pounds per year, delivered in a diffuse manner by stormwater runoff.
"Planning area" means a designated portion of the parcel
						on which the land development project is located. Planning areas shall be
						established by delineation on a master plan. Once established, planning areas
						shall be applied consistently for all future projects.
"Sand filter" means a contained bed of sand that acts to
						filter the first flush of runoff. The runoff is then collected beneath the sand
						bed and conveyed to an adequate discharge point or infiltrated into the in-situ
						soils.
"Shallow marsh" means a zone within a stormwater extended
						detention basin that exists from the surface of the normal pool to a depth of
						six to 18 inches, and has a large surface area and, therefore, requires a
						reliable source of baseflow, groundwater supply, or a sizeable drainage area to
						maintain the desired water surface elevations to support emergent
						vegetation.
"Stormwater detention basin" or "detention basin" means a
						stormwater management facility that temporarily impounds runoff and discharges
						it through a hydraulic outlet structure to a downstream conveyance system.
						While a certain amount of outflow may also occur via infiltration through the
						surrounding soil, such amounts are negligible when compared to the outlet
						structure discharge rates and are, therefore, not considered in the facility's
						design. Since a detention facility impounds runoff only temporarily, it is
						normally dry during nonrainfall periods.
"Stormwater extended detention basin" or "extended
						detention basin" means a stormwater management facility that temporarily
						impounds runoff and discharges it through a hydraulic outlet structure over a
						specified period of time to a downstream conveyance system for the purpose of
						water quality enhancement or stream channel erosion control. While a certain
						amount of outflow may also occur via infiltration through the surrounding soil,
						such amounts are negligible when compared to the outlet structure discharge
						rates and, therefore, are not considered in the facility's design. Since an
						extended detention basin impounds runoff only temporarily, it is normally dry
						during nonrainfall periods.
"Stormwater extended detention basin-enhanced" or
						"extended detention basin-enhanced" means an extended detention basin modified
						to increase pollutant removal by providing a shallow marsh in the lower stage
						of the basin.
"Stormwater retention basin" or "retention basin" means a
						stormwater management facility that includes a permanent impoundment, or normal
						pool of water, for the purpose of enhancing water quality and, therefore, is
						normally wet even during nonrainfall periods. Storm runoff inflows may be
						temporarily stored above this permanent impoundment for the purpose of reducing
						flooding or stream channel erosion.
"Stormwater retention basin I" or "retention basin I"
						means a retention basin with the volume of the permanent pool equal to three
						times the water quality volume.
"Stormwater retention basin II" or "retention basin II"
						means a retention basin with the volume of the permanent pool equal to four
						times the water quality volume.
"Stormwater retention basin III" or "retention basin III"
						means a retention basin with the volume of the permanent pool equal to four
						times the water quality volume with the addition of an aquatic bench.
"Vegetated filter strip" means a densely vegetated
						section of land engineered to accept runoff as overland sheet flow from
						upstream development. It shall adopt any natural vegetated form, from grassy
						meadow to small forest. The vegetative cover facilitates pollutant removal
						through filtration, sediment deposition, infiltration, and absorption and is
						dedicated for that purpose.
"Water quality volume" means the volume equal to the
						first 1/2-inch of runoff multiplied by the impervious surface of the land
						development project.
Statutory Authority: §
													62.1-44.15:28 of the Code of
						  Virginia; Chapters 68 and 758 of the 2016 Acts of
						  Assembly.