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Appendix - Arden Hills Water Quality Task Force - June 2000 . homes. 1bis gives residents the option to walk rather than drive and thereby eliminate some of the 12 automobile trips that the members of an average suburban household make each day.38 Other Non-Structural Methods- Water Quality Education Programs The most successful of the education/outreach programs accomplish three goals. First, they educate people about the nature of the urban stormwater pollution problem -- its causes and consequences. Second, they inform people about what they can do to solve the problem. Finally, since hands-on education is often the best, the program achieves either pollution reduction or restoration targets. "Post Construction Stormwater,Management -The management and planning methods.usedto reduce the overall impact of stormwater from developed, or developing, areas. The primary activity of most municipal and Watershed control organizations. Pre-Construction Stormwater management- The identification of issues and planning for water quality management prior to construction. Includes public education, construction site controls, elimination of illegal and harmful discharges, and improved municipal housecleaning practices. Studies and case histories have shown these methods to be more effective and more cost effective than post construction management. Structural BMP's - Detention practices Temporarily store runoff, then discharge it through a pipe or other outlet structure into streams or other waterbodies.43 Use ofwet and dry detention ponds are the most common such practices. Dry ponds release all of their water within a specified time period (generally up to 48 hours), while wet ponds keep some water at all times and retain excess water for a longer period than dry ponds. When designed to be such, wet ponds can be an aesthetic or recreational amenity. Another less common detention practice is the use of cistems. Detention ponds allow warm stormwater to enter directly into receiving waters. Stormwater collected in ponds may heat to 950 F or more on a hot summer aftemoon.51 Since aquatic ecosystems are sensitive to changes in water temperature, these warm waters can cause a loss of fish and other aquatic organisms e Bioretention & Biofiltration These practices filter stormwater to reduce contaminant loading using plants as an additional filter medium. Plants absorb nutrients and metals to a certain extent and facilitate microbial breakdown, but most of the pollutant removal from these practices occurs when the presence of the plants physically blocks the stormwater flow, slowing the flow and allowing contaminants to settle out. One example of this structure are called raingardens. Municipalities may use several types of biofiltration. Constructed wetlands are artificial versions of natural wetlands, using shallow bodies of standing water filled with reeds and other wetland vegetation to filter the water. Engineered filter strips are slightly sloped, flat land planted with grasses, trees or other vegetation which remove stormwater pollutants as the stormwater moves gently across the strip in a even, sheet-like flow. Swales are wide ditches with moderate sloped banks and bottoms covered with filtering turf; in many cases swales also permit infiltration as well as clean the water. Bioretention areas are constructed forested or vegetated beds, usually composed of gravel, soil, trees and shrubs, a sand layer, and a grassed swale. . Infiltration practices Temporarily store runoff in basins from which the water percolates slowly into the soil below. Like detention practices, they reduce peak flows. However, infiltration practices also recreate, to a greater or lesser extent, the natural pattern of water infIltration into the ground that existed before increased imperviousness covered the land. When designed and installed correctly and maintained regularly, infiltration practices are among the most effective structural BMPs, and often address most of the stormwater impacts previously discussed. Studies have shown that infiltration can get 98 percent of stormwater into the earth, cool stormwater to 550F, remove up to 83 percent of nitrogen, and remove up to 98 percent of copper.45 The principal reason why infiltration is often a preferred method is that runoff is cooled as it flows though the ground, thereby reducing the detrimental thermal effects that runoff has on aquatic ecosystems. "Retention" basins look like dry detention ponds, but have no outlet, forcing water to infiltrate through the bottom of the basin.46 Infiltration trenches are generally filled with rocks and gravel to surface level, creating a reservoir that holds water until it passes into the surrounding soil. Dry wells are deeper, narrower versions of infiltration trenches. Some of the most successful are wide- spread use of ''French drains," small infiltration trenches placed at the bottom of the discharge pipe from roof gutters that allow water to infiltrate on site rather than passing into the storm sewer system.