06/10/2020 P&Z Packet - Laserfiche WebLink

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Ms. Katie Larsen 06/03/2020 Page 3 Applicant to review the use of tip out curb along the edge of the proposed parking lot as shown on sheets C1.20 to C1.22 in the final plat to make sure that drainage is properly directed to storm sewer. Applicant to review and clearly show the erosion control methods proposed to protect the 239 and 241 Woodridge Lane properties near the pond outlet (Sheets C1.50 to C1.52). Applicant shall review existing TOPO shots and update existing contours. Currently, the existing contours show a 10-ft hill on the west side of the intersection of Gateway and the private road. This hill does not exist. • Stormwater Management The Lyngblomsten development is 20.74 acres in size, with an existing impervious area of approximately 2 acres. Majority of the site runoff is towards the west where there is an 24 inch diameter pipe outlet and to the existing wetland on site. The proposed impervious area is approximately 9.5 acres. There is a proposed pond located in the middle and east side of the site. The City adopts Rice Creek Watershed District's (RCWD) rules for water quality and quantity requirements. The applicant is proposing a stormwater reuse system that will be further reviewed with the final design. The current submittal now includes rate control via a combination of a dry pond (located in the northwest) and a stormwater treatment pond. The submittal normal water level of the pond is 896, and the 100 year elevation of the pond is at 900.5. CAPROC from RCWD has been obtained. (AJA 2020-05.08) It is not clear on the plans where the Porous Baffle Basin and Floating Head Skimmer are proposed. The applicant shall submit additional information for review. The plans have been modified to show the location of erosion control devices. See sheets C1.50-CI .52. These erosion control devices will be reviewed with the final design submittal. Noted. (AJA 2020-05.08) In the plan and modeling, the applicant shall update the NWL of the pond to be at, or above, the elevation of 897.0. This is the conservative estimated seasonal ground water elevation provided by Braun in the Geotechnical Report. a. The applicant shall also verify all HWL and freeboard requirements are still met. The normal water level lies been adjusted The City is comfortable allowing the NWL of the pond to be constructed below the ground water elevation if the pond is lined with a 1.0-foot clay liner. Please provide an updated plan, HydroCAD model/discharge rate calculations, water quality calculations, and irrigation calculations. Stormwater report has been included in this submittal. (AJA 2020-05.08) Ok. 2-ft clay section is shown in stormwater pond section detail on C2.11 The City's standard outlet control structure shall be used without a Fluidic -AMP Hydrobrake. The HydroCAD model shall reflect this. The fluidic amp Hydrobrake has been included in the model to allow for Rice Creek Watershed District's required 80% reduction inflow rate. If a standard orifice where to be used, it would be small enough where we are concerned about clogging of the actual orifice. The Hydrobrake provides a reduced flow yet allows for the passing of a larger sphere. The model has not been updated. The applicant has communicated to us that this outlet has been changed and modified to be a v notch weir with a 10 inch orifice at outlet. See included stormwater report for information on the proposed weir / orifice. (AJA 2020-05.08) Lyngblomsten Preliminary Plat Engineering Review