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� • Impervious Coverage Deviation Application 2060 Chatsworth Court Roseville, MN 'I'he impervious coverage of the planned build of the above home is 2% over the accepted amount of imperious coverage. The deviation amounts to 400 sq. ft. ln order to mitigate the deviation a rain garden will be installed at the rear of the lot and will incorporate the existing storm drainage manhole. The planned rain garden will be 11 ft by 11 ft. It will be 15 inches deep with 12 inches of coarse, sharp sand on the bottom covered by 3 inches of rock. The rock will help to reduce debris that is carried by the rainwater and might otherwise enter the Storm Drainage Manhole. As you can see from the Cenificate of Survey the majority of the runoff from the lot is directed toward the back of the lot where the Storm Drainage Manhole is located. The soil at the site is a mixture of sand and clay with the site being located more that 30 feet away from the downspouts. The size of the rain garden was determined using the following calculations as suggested by the W isconsin Department of Natural Resources DNR Publication PUB-WT-776 2003. "Having estimated the drainagc area, soil type, and depth for your rain �ardc�i, use Tahle 1 or T��hlc 2 to determine the rain garden's surface area. [Jse Table 1 if the rain garden is less than 30 feet from the do�� ns��o�it, :t�i�l u�c Tatale 2 if it is i��oi•e than 30 fcet t�r��it� t�l�c do�sn�poi�t. l�ablc I: 12ain gardcns less th�n 3U t'ect from downspout. 3-5 in. deep 6-7 in. deep S in. dcen Sandy soil 0.19 0.15 0.08 Siltv soil 0.34 0.25 0.16 Cla,yey soil 0.43 0.32 0.20 Table 2: Rain gardens more than 30 feet from downspout. Size Factor, for atl dcpths Sandy soil 0.03 Silt,y soil 0.0(i Clayey soil O.IU l. Find the size factor for the soil t��pc and rain gardcn de��th. 2. Multiply the size factor by the drainage area. This number is the recommended rain garden area. 3. If the recommended rain aarden area is much more than 300 square feet. divide it into smaller rain gardens.°' To mitigate 400 sq.ft-using clay as the soil type: 400 X.10 = 40 sq. ft. We are pro�osing a 121 sq ft garden, which includes the 3 sq. ft storm drainage manhole.