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Environmental Impacts <br /> With the addition of a concrete skate park to Orono Park, considerations must be made to <br /> adequately manage the increase in runoff due to the addition of the impervious area. Using <br /> Spade Model as a baseline,the predicted runoff will be 500 cubic feet during a normal rain <br /> event. This was determined by using 1.1" of runoff for a net increase in impervious surface <br /> area, a value recommended by the Minnesota Pollution Control Agency as representative <br /> for a typical Minnesota rain event.To treat this runoff,the use of a rain garden or swale <br /> ditch to is recommended. Based on the sizing recommendations of RainScaping,an <br /> environmental and rain garden planning site,the rain garden should an area of roughly 750 <br /> square feet to treat the runoff from the 6000 square foot skate park. By placing the rain <br /> garden the length of the skate park at the base of the 1% overall grade of the concrete slab <br /> the dimensions of the garden would be 105 feet by 7.5 feet,at a depth of 8". <br /> Not only would the rain garden be aesthetically pleasing and increase the beauty of Orono <br /> Park,the garden would also decrease the overall estimated cost of the skate park as well as <br /> protect Orono Lake from the possible runoff sediment pollution.The typical rain garden <br /> will cost$10,000 to install,based upon MnDOT standard pricing per unit; in comparison, <br /> the installation and materials for storm water treatment in the recently installed Oakdale, <br /> Minnesota skate park cost$32,000. In addition,the rain garden will provide a natural filter <br /> for the runoff which permeates into the ground,which will significantly decrease the risk of <br /> sediment or other pollutants reaching Orono Lake. <br /> 8 <br />