10/13/2021 P&Z Packet - Laserfiche WebLink

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Ms.Katie Larsen 10/6/2021 Page 2 supposed to drain (i.e. the area between the north edge of the pond and the curb for Rosemary Way and the area along the west edge of the Lot 2 parking lot entrance). • Stormwater Management The stormwater on the site flows to two different places. The southern portion of the site flows to a culvert located in the southeast corner that drains to the City of Hugo. The northern portion of the site flows to the north to an existing wetland in the northwest corner of the site. All of the stormwater from the site eventually flows to Clearwater Creek, which is an impaired water located approximately 0.4 miles south of the site. The surface water will flow to a new wet sedimentation basin. Storm sewer is proposed to collect water from the parking lot and road and then direct it to the proposed Stormwater Pond 10P. Some runoff will first be passed through Low Area 20P, before ultimately draining to the basin. Pond 10P is designed to discharge southeast to the existing ditch and culvert system. After the project is completed, the site will include approximately 2.42 acres of new impervious surfaces including the streets, parking lots, and rooftops. Groundwater elevations ranged from 908 to 912 throughout the site and no groundwater was detected where the pond is being proposed. Soils consist primarily of sandy lean clay, and clayey sand. Due to these soil types, infiltration is not feasible. The applicant used a HydroCAD model based on the Atlas 14, 24-hour storms to design the storm sewer conveyance system and basin. The site is designed to reduce site runoff rates for the 2-, 10-, and 100-year rainfall events. Pre-and Post- Development Discharge Rates (cfs) Condition 2-Year 10-Year 100-Year Pre- 3.8 10.4 4.2 Development Post- 3.8 10.0 2.2 Development Post-development stormwater discharge rates are less than the pre-development rates. Comments: 1. Storm sewer information shall be provided on the Belland Farms plans in addition to the AECP plans. 2. Applicant shall provide an outlet for the wetland 5 in Outlot B. 3. The location of the 5" orifice restriction in the outlet at the bottom of the structure is prone to plugging. Recommend providing a minimum of 1-foot below the orifice. 4. Confirm the HWL of Low Area 30P. The plans indicate a HWL of 917.7. However, the low area connects to the wet pond that has a HWL of 918.3. Sim-Routing or other methodology may be needed to accurately reflect the connection between the low area and pond. Belland Farms&Associated Eye Care Partners Engineering Review