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if- <br />i. <br />January 3, 1991 <br />Fairway Hills Add. <br />Page 3 of 3 <br />3. Surface Drainage <br />Surface water flow through the site appeairs to be intennittent. There is <br />no clear estedslished drainageway through part of the wetleu:^. can <br />the high water information provided by the MNDOT TH 12 plans, we have <br />cxarputed expected flows frcan a 100 year storm to be 19 cfs, and have <br />provided two 18" culverts under the driveway to accomnodate this water. <br />We suggest that these culverts be placed at a relatively flat grade and <br />at an elevaticnn which will pass the 100 year storm without an increase <br />’’n hi^ water elevation. We also suggest that, to maintain the character <br />of the wetland, no specific channel be cxanstructed connecting the <br />existing culverts. Seme annual maintenance of this cnilvert may be <br />required. <br />4. Stormwater Detention <br />The regulations of the watershed require on-site stormwater detention <br />sdiere runoff flows are a’tered. Constructicn of two houses and the <br />driveway wcjuld cover alxut .55 acre with in^jervious surfacing or 9% of <br />the site. In our preliminary cxxtversaticxis with Mr. Ron Quanbeck from <br />the waterslied, he indicated on-site detent icon may not be rec^uired for <br />this development. <br />If it is determined that stormwater detention is necessary, the areas <br />southeast of the driveway in Lot 1 and north of the house in lot 2 would <br />be adequate for this purpose. <br />Summary <br />This information is provided to assist the City in their review of the <br />projeert. CXir primary focxis was for the drainage/wetland considerations, <br />but we have also included a preliminary design for driveway and utility <br />construction. <br />In our opinion, the improvements shown will meet the requirements of the <br />City and Watershed regarding site drainage and wetland emcroachment. <br />Please contact me if you have any questions regarding this letter. <br />Sinoeraly, <br />.:. V . <br />A. Andersen, P.E. <br />Attaednnents <br />••• ♦»*. <br />i. . • ■■•mi- . <br />Si, <br />oc: Ran Hopkins <br />Gary Mroz <br />.Lot Surveys _ _ _ _ <br />■ . ' <■ » - : , .. . . i • . • _. . . . . . . . . . . . . . . . . ....... ... ... . ‘ . . . . . .- ^ *• •- ' . J 1 ^ _ .... . ............ <br />e- .*»•#, •.*•= <br />r ^ .* <br />..rMMMKskAuttih..,