11-08-07 Planning Comm. Agenda - Laserfiche WebLink

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Planning Commission October 5, 2007 Page Two 3. The current hydrant spacing is insufficient to meet city standards and it appears that the addition of a hydrant will be necessary. We would recommend that a hydrant be added between Lots 1 and 2. 4. All utilities should be shown in a profile view. The minimum storm sewer pipe size for pipe runs other than leads to single catchbasins is 15-inches. 5. Standard detail plates should be included in the final plan set including specifics on the pond outlet structure. Drainage Calculations The existing drainage area map does not depict the existing conditions correctly. There is a low area located to the east side of the middle of the proposed development. A third drainage area should be created that drains to this low area and provides existing ponding. 2. Infiltration basin 2P in the proposed calculations should be revised to reflect the proposed contours. The top contour is currently noted as 915.0 and the calculations should be modified to reflect this. All ponding/storage area utilized for 2P should be within a drainage and utility easement. 3. The time of concentrations provided should each be calculated based on a path and not a direct assumption. Flow paths that correspond to the time of concentrations used in HydroCAD should be noted on the drainage maps. 4. Infiltration Pond 1P should be revised within the proposed drainage calculations. The starting elevation of the silt basin pond should be modified to 912.8, which corresponds to the overflow noted on the plans. The silt basin area cannot be used for exfiltration. The exfiltration surface area can only be modeled for the infiltration/ponding basin. Infiltration pond P1 should be modeled as two separate ponds. 5. The time span for the HydroCAD calculation should be changed from 2.00-24.00 hrs to 0.00-24.00 hrs. A fu1124-hour period should be accounted for. 6. Documentation should be provided as to the basis of the infiltration rates being used in the calculations. 7. Storm water pipe calculations should be provided for verification of pipe sizes. Preliminary Plat 1. Front footage should be verified at the building set back line to ensure they meet a minimum width of seventy-five feet for Lots 5, 6, and 7. 2. Additional drainage and utility easement may be necessary on Lots 6 and 7 depending on proposed contours that are added. All drainage from Lot 7 across Lot 6 should be covered. An access path to the infiltration pond in the northwest corner of the site should also be designated and covered by a drainage and utility easement for City access to the pond with maintenance equipment. 2 Z:\PROJ\120101E -Whispering Pines\Itr-100507-PC.doc