06/11/2014 P&Z Packet - Laserfiche WebLink

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Ms. Katie Larsen June 5, 2014 Page 2 ■ Pond 2 storage is modeled incorrectly — the elevation -area relationship is mistakenly representing the area in acres, rather than square feet. ■ Revise the curve numbers based on RCWD Rule C values (HSG B is 61 for existing pervious areas and 74 for proposed pervious areas to account for soil compaction during construction). ■ The time of concentration for all catchments, in both existing and proposed models, is 0 minutes, please update the calculations. ■ Please include the 7.2-inch 100-year 10-day snowmelt event to determine critical water surface elevation. ■ The project as shown only treats 5 1 % of the impervious surfaces with Ponds 1 and 2; RCWD allows a maximum of 15% of the impervious surfaces may be left untreated (at least 85% of the impervious surfaces must be treated before leaving the site). 2. Grading and Erosion Control Plan ■ Label ponds, normal water elevation and high water elevations ■ Pond 2 contours are mislabeled ■ Verify slopes are no steeper than 3:1, especially in pond areas ■ Show emergency overflow locations and elevations ■ Show driveways and include in the impervious area calculations ■ Show the existing house low floor and low opening elevations ■ Low opening freeboard not being met for Lot 3 (low floor elevation 910.5, minimum is 910.83) ■ Three-foot groundwater separation may not be met for ponds; pond bottom at 906, soil boring from May 8, 2014 has a water depth of 5.5-ft below grade (approximate elevation of 903.5), minimum pond bottom elevation would then be 906.5. ■ Legend lists rain gardens and infiltration areas, but missing the line types and labels to indicate where these features are located on the plan. 3. Pre -Development Drainage Plan: ■ Turn off proposed contours ■ Turn off "proposed grinder pump station" shown at the southeast corner of catchment X3 4. Post -Development Drainage Plan: ■ Pond 2 contours are mislabeled ■ Verify pond elevation -area relationships — the HydroCAD model has two identical ponds, but the grading plan shows different grading. ■ Label ponds, normal water elevation, high water elevation and emergency overflow locations and elevations. Administrative: ■ The applicant must provide an operation and maintenance agreement for stormwater facilities. This agreement must be recorded against the parcel so that it transfers with future sales of the parcel. This may be included as a part of the Developer's agreement with the City. ■ The applicant must receive permits from other agencies prior to construction. Permits needed may include the MPCA's NPDES Construction Stormwater Permit and RCWD's Stormwater Management and Erosion Control permits. Grading Comments: 1. Benchmark or datum not shown on grading plan.