16628 - SWMP - Tanager Creek 1-18-2022

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Stormwater Narrative/Summary December 5, 2021 Tanager Creek Orono, MN 2 | P a g e Project Overview Tanager Creek is a proposed 3-lot residential development in Orono, MN. The site encompasses 14.06 acres. The property is located in Hennepin County and within the Minnehaha Creek Watershed District. The project will require an Erosion Control Permit and Stormwater Management Permit from Minnehaha Creek Watershed Distict. The project includes site clearing and demolition of existing structures and pavement found on site. The proposed development will consist of 3 residential lots, each with over a half acre of upland. A private street and cul-de-sac is proposed to provide access off Brown Road. Existing Site Conditions The 14.06-acre property is located on Brown Road (Co Rd 146) in Orono, MN. Runoff is generally directed to the north and east, entering a wetland area that is contiguous with Lake Minnetonka. The existing site features a single-family residence with detached garage and bituminous paved driveway. The area surrounding the residence is vegetated with turf grass with scattered trees beyond. The existing drainage pattern can be seen in Exhibit A: Existing Drainage Map within the appendices of this report. The property is does not have city water or sewer services and is instead served by private well and septic. Soils County Soils data indicates the in-situ soils are Angus Loam which consists of loam and clay loam. These soils area classified as Hydrologic Soil Group C. For our hydrologic modeling we used curve numbers for “B” soils for the existing conditions and “C” soils for the proposed conditions. Proposed Site Conditions The proposed development will consist of 3 single-family residential lots served by a short private street with cul-de-sac. Each lot is proposed to be served by a paved driveway. The post-developed impervious surface area will increase by 14,487sf. Due to the restrictive onsite soils and limited space to implement a conventional stormwater BMP, the project proposed to construct a filtration basin to provide stormwater treatment. The proposed filtration basin includes retention of 2,498 cubic feet of runoff for filtration prior to outletting into the wetland area. The proposed grading plan allows for overland drainage of the private street and front of the proposed lots, as well as all runoff from Lot 1 and an additional area of Lot 2 to be routed to the filtration basin. The grading also takes advantage of an area proposed to remain undisturbed as a filter strip to provide pretreatment of runoff. The proposed drainage pattern can be seen in Exhibit B: Proposed Drainage Map can be found in the appendices of this report.