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Stormwater Management Plan <br />Inwood Commercial <br />Carlson Engineering, Inc. Page 3 of 6 <br />STORMWATER ANALYSIS <br /> <br />The proposed site is part of a master development known as Inwood. The site was mass graded <br />in 2015, including grading for the Inwood Commercial and adjacent commercial lots. As part of <br />the mass grading, two regional stormwater ponds and a regional infiltration basin were <br />constructed to provide water quality treatment and rate control for the area in question, as well <br />as portions of the residential area to the west. The analysis presented below is based on a review <br />of the approved Inwood Stormwater Management Plan prepared by Carlson Engineering, last <br />revised February 16, 2015. <br /> <br />1.4 Peak Elevations <br /> <br />Based on the Inwood Stormwater Management Plan, the table below summarizes the existing <br />high water levels for the existing Ponds 100 and Infiltration Basin 400 located south of the existing <br />Kwik Trip, and Pond 200 located immediately east of the site. <br /> <br />Table 1 <br />High Water Elevations <br />Inwood Development <br />Lake Elmo, Minnesota <br />Basin Bottom Outlet 2y HWL 10y HWL 100y HWL <br />Pond 100 986.0 995.0 996.9 998.1 1000.7* <br />Pond 200 996.0 1006.0 1007.9 1008.9 1011.0* <br />Basin 400 994.0 995.0 996.6 997.5 998.6* <br /> <br />*Note the revised HydroCAD model and final grading plans for Inwood list the 100-year HWL <br />for Pond 100 at 1001.3, for Pond 200 at 1010.4 and for Basin 400 at 998.8. <br /> <br />The previously approved Inwood development stormwater management plan accounted for a <br />maximum allowable impervious area of 3.330 acres of the proposed site to flow to Pond 200. <br />The current Inwood Commercial plan is proposing a total of 3.184 acres of impervious (from the <br />public streets and ghost plat lots) to Pond 200. Therefore, the approved Inwood stormwater <br />plan is more conservative than the proposed Inwood Commercial layout, and Pond 200 will see <br />no adverse effects of the full build out of Inwood Commercial. Pond 100 is in a similar situation <br />with a maximum allowable impervious area of 2.850 acres, which was previously accounted for <br />in the approved Inwood stormwater plan, and a proposed impervious area of 2.377 acres with <br />Inwood Commercial development. Thus, Pond 100 will see no adverse effects from the full <br />build out of the Inwood Commercial site. <br /> <br /> <br /> <br />