04-17-2000 Planning Packet - Laserfiche WebLink

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Site Modifications • tv ••• The existing property is used for other seasonal purposes in addition to the salt sand operations during the fall and winter months. The proposed storage building would be located in the northeast comer of the property which is currently used to store the Lake Minnetonka Conservation District (LMCD) milfoil harvesters. To continue accommodating the storage o: dne milfoil harvesters, a proposed storage area would be provided in the northwest comer of the rroperu'. The storage area would be 68' W X 141* L with an 8" deep aggregate surface. The grade of the storage area would be 0.5% east toward the existing bituminous. Tlie storage area drainage would flow east and south to an existing 18" CMP culvert which outlets into Wetland #1 in the southwes: comer of the property. The area east of the existing bituminous mat and including the storage building and 10' perimeter would be changed from a gravel surface to a bituminous surface 147' X 257 ’ L consisting of 6" of bituminous and 8" of granular material. The grade of the proposed biouuinous mat would be 0.9% toward the southeast. The drainage would flow to Wetland #3 in the soumeasi comer of the property. The proposed bituminous area would provide a stable maneuv ering arei for vehicles and a surface for aggregate stockpiling. The grading excavation necessary for the improvements would be apprrximately 400 C.Y. for the milfoil harv'ester parking area, 1,500 C.Y. for the Pond A grading, and ".000 C.Y. for the salt storage building site including the three swales and bituminous mat. The salt s*.::age building footing excavation would be additional and dependent on the footing design. Stormwater Management The building location in the northeast comer of the property is the farthest practical location from the wetlands receiving stormwater runoff from the site. This location will maximize the time of concentration allowing the turf areas to filter stormwater runoff. The existing drainage flow is to three separate wetlands located on the south side of the property. The existing wetlands are referred to as Wetland #1, Wetland #2 and Wetland #3 from west to east. The peak rate of stormwater mnoff would be limited to the predevelopment condition. The hydraulic anal> sis is being performed and will be forwarded immediately upon completion. The runoff shall be ar.alyzed for events of critical duration with return frequencies of 1,10 and 100 years which is critehc.” set by the Minnehaha Creek Watershed District under Rule N. The proposed drainage closely mimics the existing with the following .T.odificaiions: • Drainage Swale 1 is 2' wide with variable depth paralleling the nors. edge of bituminous with 0.3% grade to proposed catch basin 2 located north of the existing bimminous and central to the property. • Drainage Swale 2 is 4' wide and 1' deep paralleling the north side c: the proposed storage building with a 0.5% grade to proposed catch basin 2. Catch basin 2 outlets through a proposed 15" plastic storm sewer pipe that flows to proposed catch basin 1. Catch basin 1 outlets into proposed Pond A through a proposed 15" plastic storm sewer with a CMP apron end section. • Drainage Swale 3 is 4' wide and 1' deep and parallels the east side c: the proposed bituminous mat with a 1 .5% grade to proposed Pond A. a