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Retention Basins: A retention basin is a stormwater facility that includes a permanent impoundment, or pool of
water, and therefore, is normally wet, even during dry periods. Inflows from stormwater runoff may be
temporarily stored above this permanent pool.
Extended Detention Basin: An extended-detention basin is an impoundment that temporarily stores runoff for
a specified period and discharges it through a hydraulic outlet structure to a downstream conveyance system.
An extended-detention basin is usually dry during non-rainfall periods. An Enhanced Extended Detention Basin
includes a shallow marsh with emergent vegetation in the basin bottom, which increases the potential pollutant
uptake.
Constructed Stormwater Wetlands: Constructed stormwater wetlands are manmade shallow pools that create
growing conditions suitable for both emergent and aquatic vegetation. Infiltration Practices: Infiltration facilities
temporarily impound stormwater runoff and discharge it via infiltration into the surrounding soil. Infiltration
facilities include Infiltration Basins, Infiltration Trenches, Roof Downspout Systems, and Porous Pavement.
Bioretention Practices: Bioretention Practices are shallow pockets or depressions underlain by an engineered
soil mixture to facilitate filtration and exfiltration into the underlying natural soils. When the natural soil horizon
below the facility is not suitable for infiltration, an under drain system is used to de-water the facility. Also referred
to as rain gardens, bioretention practices include a landscaping plan of specific plant species which results
in an aesthetic site feature, as well as a water quality BMP.
Sand Filters: Intermittent sand filter facilities are underground vault-like facilities that capture, pre-treat, and
filter the first flush of stormwater runoff. In some cases these facilities can include an above ground storage
facility to store the excess volume of runoff from larger storms.
Grassed Swale: A grassed swale is a broad and shallow earthen channel vegetated with erosion resistant and
flood-tolerant grasses. Check dams are strategically placed in the swale to encourage ponding behind them. A
Water Quality Swale is a broad and shallow earthen channel vegetated with erosion resistant and flood tolerant
grasses, and underlain by an engineered soil mixture to facilitate filtration and exfiltration into the underlying
natural soils. When the natural soil horizon below the swale is not suitable for infiltration, an under drain system
is used to dewater the swale.
Vegetated Filter Strip: A vegetated filter strip is a densely vegetated strip of land engineered to accept runoff
from upstream development as overland sheet flow. It may adopt any naturally vegetated form, from grassy
meadow to small forest. All stormwater management structures must be maintained to remain effective.
Non-Structural BMP’s
Nonstructural BMPs include any efforts to minimize the impact of the activities on, and the improvements to, the
land surface on the aquatic environment
• In most states a Stormwater Pollution Prevention Plan (SWPPP) must be written and updated and
include the following requirements:
- Used oil management
- Spent solvent management
- Proper disposal of spent abrasives
- Disposal of vessel wastewater
- Spill prevention and control
- Safe fueling procedures
- General good housekeeping
- Appropriate painting and blasting procedures
- Used battery management
A sample SWPPP is attached at the end of this document, Appendix A
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