Agenda - Council - 06/13/2017 - Laserfiche WebLink

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COVENANT MEADOWS Storm water summary Rev 5-4-17 Covenant Meadows is a 12 lot proposed single family residential subdivision that lies roughly at 173rd Ave NW, Germanium St NW and Trott Brook in the City of Ramsey. Three ponds are proposed for the site. All will be infiltration type. This type of ponding was chosen as no storm sewer or other viable outlets exist on the site. All ponds retain the 100 year storm event. An area of direct runoff will occur. This is created by the connection of the property to Germanium Street. This strip of land does not provide an area to treat storm water. Per attached HydroCad analysis, the 2, 10, 100 year release rate is 1.10, 1.65, 2.74 cfs vs 0, 0.09, 3.15 cfs existing respectively. With pool volumes less than 3 feet deep for the 100 year event and an infiltration rate of .8 inches per hour, dry time for the ponds will be less than 48 hours. ATLAS 14 rainfall rates were used to analyze the system as depicted in the attached HydroCad Report. Steep slopes exposed to water are not proposed for this project. No wetlands are located on the site. Site soils are sands with the exception of the area by the NE Pond and SE Pond. A clay layer is found here. This layer will be excavated to access the well draining sands beneath. Sand will be loosely placed in the excavation to promote water absorption into the ground. The area of development is 11.6 acres. The impervious area of the plat is 2.30 acres. The impervious is comprised of housepads, driveways, and streets. Silt fences will be placed after pond construction to prevent soils from depositing into the ponds. Pond grading and seeding notes are found on the attached plans.