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u • Impervious Coverage Deviation Application 2060 Chatsworth Court Roseville, MN The impervious coverage of the planned build of the above home exceeds the allowable amount. The deviation amounts to 539 sq. ft per Bryan Lloyd, Associate City Planner. In order to mitigate the deviation a rain garden will be installed at the rear of the lot. See attachment. The planned rain garden will be 11 ft by 5 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 Certificate of Survey the majority of the runoff from the lot is directed toward the back of the lot where a 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 Wisconsin Department of Natural Resources DNR Publication PUB-WT-776 2003. "Having estimated the drainage area, soil type, and depYh for your r�in �;�orden, use T�blc ( u�• T��blc• 2 to determine the rain garden's surface area. Use Table 1 if the rain garden is less than 30 feet from the downspout, .�n�! usc �C�3hl�'_ if �t es en«rc th��n 3il fee�t 1�rom the d��e�ss�out.�" 7�able 1: Rain gardens less than 30 feet from downspout. 3-5 io. deep 6-? in. decp K i�i. dec� Sandy soil 0.19 0.15 0.08 Siltv soil 0.34 0.25 0.1(, ('la��c�� soil 0.-t3 0.32 O.2U ('abl�: 2: 12ain �arden�ti morc than 30 fce� from do��nspout. Size Factor, for all dcpth� Sandy soil O.t13 Siltv soil O.U(i Clayey soil 0.➢ff 1. Find the size factor for the soil t��pe and rain �arden deptho 2. Multiply the sizc factor by thc drainagc area. This numbcr is flac recun��mcnded rain garden area. 3. ITthe recummcndcd rzzin �;�u•den �rca is nruch �n��re thzan 3QU �qu:�re fc�t, di� itle it into smaller rain �ardcn5a" To mitigate 539 sq ft-using clay as the soil type: 539 X.10 = 53.9 or 54 sq. ft. We are proposing a 55 sq ft garden.