Some examples of post-construction storm water controls:
Infiltration / Filtration Basins are open earthen impoundments designed to retain storm water and to infiltrate it into the soil. The design should include an inlet-settling basin to remove coarse materials prior to flowing into the infiltration basin. The surface may or may not be vegetated. Infiltration basins are used when you have permeable soils to accept the water, filtration basins have drain tile systems that collect the filtered water and discharge it to a storm sewer.
Infiltration / Filtration Trenches are trenches that are 1 to 2 feet wide, and 2 to 10 feet deep. They are typically lined on the sides and bottom with permeable filter fabric and backfilled with coarse aggregate. Trenches may be surface or subsurface levels, and design may include a vegetative filter strip. Trenches are effective in removing suspended sediments, floating debris, and bacteria. In most cases, trenches will have some overflow connection to the storm sewer. Infiltration trenches are used when you have permeable soils to accept the water, filtration trenches have drain tile systems that collect the filtered water and discharge it to a storm sewer.
Pervious (Permeable) Pavement is a structural support surface that allows water to flow through the material into a subsurface of gravel or rock, and ultimately into the soil or other post construction storm water control. Pavements can be made of concrete, asphalt, plastic, or composite materials. They can look like standard concrete or asphalt pavement, paving block or even grass.
Swales are vegetated, shallow channels with gentle side-slopes. Treatment occurs as storm water flows through the dense vegetation. Removal mechanisms for pollutants include filtration, sedimentation, adsorption, and infiltration into the soil profile. Swales are used to remove sediment and pollutants that adhere to the sediment.
Filter Strips are vegetated, gently sloped strip, 10 feet or more in down-slope length (50 to 75 feet is recommended for good performance). Vegetation may be turf, or forested with trees and shrubs. Filter strips must be designed to accept sheet flow, and are typically used in conjunction with other treatment control measures, such as grassy swales or infiltration trenches.
Rain Gardens and Bio-retention Areas are gardens that collect, filter and use storm water reducing the amount of water discharged to a storm water system. Flowering plants and grasses (preferably native species) that can withstand a cycle of flooding and drought are usually used.
Underground Detention devices are tanks that can take large volumes of storm water quickly and then slowly discharge that water back into the storm water system. Underground systems are usually more expensive than other systems, but are useful on small sites.
Best Management Practices: New Practices will be added as they are completed.
To reduce the impact of the Duluth campus we will look into building infiltration / retention / detention centers. This would include design and possible modifications to existing wet ponds for retention capabilities, and the design and possible construction of new facilities. New facilities may include rain gardens, bio-retention, sand filters, etc.
We will also be looking for ways to protect our creeks by develop setback requirements, improving shade for trout streams and protecting shorelines against erosion where necessary.
As a non-traditional MS4, the University does not have traditional "regulatory mechanisms." It relies on administrative procedures and contractual relationships to ensure compliance. University Construction Standards, which are incorporated into contracts with Architect/Engineering (A/E) firms, already require construction projects to include post construction controls, specifically requiring all new projects to ‘reduce impacts on receiving waters with a goal of no net increase in volume, rate or pollutant loading.’
The following is from the University of Minnesota Standards & Procedures for Construction and current as of December 2006. "7. Sustainable Design Requirements - 7.3.2. Sustainable Sites: This includes development in environmentally appropriate areas, reduced site disturbance, proper storm water management and sustainable landscape design." Please check http://www.cppm.umn.edu/standards/ProgramInformation.pdf for updated requirements.
As a non-traditional MS4, the University of Minnesota Duluth will be the final owner of all installed structural BMPs. These BMPs will be operated and maintained as part of our on-going maintenance of the campus.
Storm water drainage wells (usually considered a class V injection well) are typically shallow disposal wells designed to place storm water below the land surface. By EPA definition, a Class V injection well is any hole that is deeper than its widest surface dimension or any subsurface fluid distribution system that releases fluids underground. Storm water management BMP's that include subsurface infiltration must comply with the EPA Underground Injection Control program. For more information see http://www.epa.gov/safewater/uic/class5/index.html or the EPA’s fact sheet "When are storm water discharges regulated as Class 5 wells".
Post-construction controls can be particularly difficult in cold weather climates due to frozen soils and ponds, and sand and salt use. The Center for Watershed Protection has a Stormwater Practices for Cold Climates manual available on line at http://www.cwp.org/Resource_Library/Special_Resource_Management/coldclimate.htm.
Several Minnesota organizations have also put out manuals that have BMP's for post-construction storm water management. Metropolitan Council Environmental Services (MCES) offers guidance on post construction storm water controls in their Urban Small Sites Best Management Practice manual, and the MPCA put out the Protecting Water Quality in Urban Areas manual
The EPA has a National Menu of Best Management Practices for Storm Water Phase II for Post-Construction Storm Water Management in New Development & Redevelopment which can be found at: http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm.