09-28-2005 Council Agenda - Laserfiche WebLink

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Storm Water Calculations 1. The drainage area map currently has the existing and proposed areas on the same map. They should be separated into two exhibits and contours should be included. The boundaries for the subcatchments appear to be the same for the existing and proposed conditions. However, the HydroCAD results have different areas listed for the two conditions. Any discrepancies should be resolved. In addition, the proposed boundary for Subcatchment Dev -North appears to be inaccurate. The boundary is shown as the north edge of the roadway. The grading plan indicates that the front of the houses and the driveways will drain to the roadway. 2. The time of concentration appears low for the Ex -North Subcatchment. The area is larger than some of the other Subcatchments; however the time of concentration is lower. This should be reviewed and corrected or documentation provided as to the shorter time. 3. The time of concentration for each area remains the same for the existing and proposed calculations even though the areas and curve numbers are different. This should be reviewed and corrected. 4. A curve number of 100 should be used for the area covered by the normal water level of the proposed ponds in Subcatchment Dev -East and Dev -West. 5. Documentation should be provided to verify that the data in the HydroCAD model is correct for the existing wetland, including area and outlet information. In addition, the starting elevation for the wetland should match the outlet elevation. 6. Documentation should be provided for the area of Subcatchment Adj -Area. 7. The maximum allowable impervious area by City Ordinance is 30 %. The curve number for Subcatchment Dev -North should be revised to reflect a 30% impervious area. 8. Dead storage calculations should be provided for review to verify that the required volume is provided for treatment. 9. A drainage area map should be provided that corresponds with the areas for each proposed catch basin to facilitate review of the storm sewer design. Miscellaneous 1. The pavement section indicated in the geotechnical report is noted as a 10 -year design life. It is required that a 20 -year design life be used. The report and street section should be revised to reflect this. These are our comments based on review of the final documents submitted. It is our recommendation that if the City Council approves the final plat, the approval should be contingent on addressing all the comments that are listed above along with all other City Staff comments. Approval should also be contingent on approval by the Ramsey Washington Metro Watershed District and all other applicable agencies. Please contact me if you have any questions regarding the above information at (763) 780 -0450. cc: Developer Pete Regnier Steve Westerhaus, Building Official