Description Intensive, decorative storm water treatment process with three-dimensional channels excavated and backfilled with a sand bed and soil, covered with a variety of vegetation and mulch. The design promotes sheet flow, which traps pollutants within the vegetation and soil.

Michigan Department of Environmental Quality, 2001.

Mechanisms A reduction in water pollutants is achieved through the use of selected vegetation, mulch, and a sand bed. The design promotes the slowing of runoff and the dispersion of flow throughout the channel area. The vegetation and soil removes pollution through biological and physical/chemical processes.

Michigan Department of Environmental Quality, 2001.

Applications Useful in reducing runoff contamination from parking lots, light traffic roadways, and other impervious surfaces. Not for use in areas with high water tables. Can be used in areas of high pollution concentration if a liner is installed. Not for use in areas with a soil clay content of 25% or greater. Reduced efficiency in cold climates. Not recommended for steep slopes. Not recommended in areas with large sediment runoff (due to clogging). Regular maintenance required. Especially recommended for areas with loamy sand soils. Flexible layout design. Requires large amounts of space relative to drainage area. Recommended for small sites due to clogging and problems associated with large flow volumes, although multiple bioretention areas can be installed for larger sites.

US Environmental Protection Agency, 2002.

 

Detailed Specifications Design Values*: Average sand bed depth of 18 inches. Bioretention area slope less than 20%. Maximum ponding depth of 6 inches. Maximum sheet flow velocity: 1 foot per second for planted ground cover. 3 feet per second for mulch. Average of 0.25 acre drainage area to one-acre bioretention area. Maximum drainage area determined for a 10-year storm event. Recommended minimum bioretention area of 15 feet wide by 40 feet long to establish a microclimate (additional calculations are required for site specific designs). Planting soils of sandy loam, loamy sand, or loam texture with 10-25% clay content and 1.5-3% organic content. Soil infiltration rates greater then 0.5 inches per hour. Soil pH between 5.5 and 6.5. Planting soil maximum of 500 ppm concentration of soluble salts. Minimum 4 feet deep of planting soil, and minimum of 4 inches past deepest root depth. Terrestrial forest ecosystems vegetation capable of handling pollutant load (native species and genotype specific to the region can be researched). Shrub-to-tree ratio of 2:1 or 3:1. Trees spaced 12 feet apart and shrubs 8 feet apart . Planting soil nutrient requirements: 35 pounds per acre magnesium. 85 pounds per acre potassium. 100 pounds per acre phosphorus. Ground cover of grasses or legumes and mulch 2-3 inches deep should be applied after other vegetation has been implemented. Mulch aged a minimum of half of a year. For more information visit: US EPA Bioretention Storm Water Technology Fact Sheet, US EPA Bioretention Post Construction Storm Water Management in New Development & Redevelopment. *Note: Local governments may use different design values than those listed above, be sure to comply with any applicable laws and regulations.

Metropolitan Council of Minnesota, 2003.

Plans

Prince George's County Department of Environmental Protection, 1993 (Cited in Metropolitan Council of Minnesota, 2003).

Prince George's County Department of Environmental Protection, 1993 (Cited in Metropolitan Council of Minnesota, 2003).

Center for Watershed Protection, 1996 (Cited in Metropolitan Council of Minnesota, 2003).

Water Quality

• 65-87% total phosphorus removal.

• 70-95% lead removal.

• 64-95% zinc removal.

• 43-97% copper removal.

• 59% total nitrogen removal.

• 52-80% TKN removal.

• 27% calcium removal.


(The capacity to remove some pollutants will become exhausted over time).


• 90% total suspended solids removal.

• 90% organics removal.

• 90% bacteria removal.

• For more information visit:
  US EPA Bioretention Storm Water Technology Fact Sheet,
  US EPA Bioretention Post Construction Storm Water Management in New Development & Redevelopment.

Maintenance

• Inspect vegetation twice per year.

• Remove litter, debris, and dead or diseased vegetation as needed.

• Prune, weed, and mow to maintain appearance.

• Replace mulch and soil in high erosion areas.

• Replace mulch every few years as needed.

• Measure soil pH 1-2 times a year.

• Apply alkaline product when soil is acidic.

• Replace soil if plant lethal pollutant levels are exceeded.

• Water daily until plants become established.

Resources

Center for Watershed Protection. 1996. Design of Stormwater Filtering Systems.

Michigan Department of Environmental Quality. 2001. Infiltration BMP’s.
: http://www.michigan.gov/deq/0,1607,7-135-3313_3682_3714-13673--,00.html (January 2006).

Metropolitan Council of Minnesota. 2003. Bioretention Systems. Urban Small Sites Best Management Practice Manual. pp. 3-181 - 3-190.
http://www.metrocouncil.org/environment/Watershed/BMP/CH3_STFiltBioretention.pdf (January 2006).

Prince George's County Department of Environmental Protection. 1993. Design Manual for Use of Bioretention in Stormwater Management.

United States Environmental Protection Agency. August 15, 2002. Bioretention. Post-Construction Storm Water Management in New Development & Redevelopment.
http://cfpub.epa.gov/npdes/stormwater/menuofbmps/post_4.cfm (January 2006).

United States Environmental Protection Agency. September 1999. Bioretention. Storm Water Technology Fact Sheet. EPA 832-F-99-012.
http://www.epa.gov/owmitnet/mtb/biortn.pdf (January 2006).

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