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<br /> If it is not feasible to capture additional on-site or off-site impervious surface, <br />please provide sufficient explanation, including documentation of the constraint <br />and an examination of what it means to remove or avoid it including modifying <br />the size, scope, configuration, or density of the proposed action. <br />o Please delineate subwatersheds based on the wetland, stormwater basins or other <br />outlet point they drain to. Provide a summary at each point of site discharge. <br /> Currently, in existing conditions a large portion of E1 would drain to Wetland 1 <br />rather than Wetland 2. Please revise drainage map such that Wetland 1 has its <br />own drainage area and update HydroCAD Model to reflect this. <br /> Not all of P1 will flow to P1i/f. Please revise grading (provide more defined <br />ditch) or drainage diagram subwatershed. A more defined ditch is needed on <br />the north end of lots 1, 2, and 3 to make sure that impervious area is actually <br />draining to filtration Basin 1. As currently graded, much of lots 1 and 2 will drain <br />directly to Wetland 1. <br /> Please place ditch behind lot 5 home to drain impervious to infiltration basin. <br /> Delineate full drainage area of Wetland 1 <br />o Please provide culvert/pipe/draintile information (i.e. complete utility plan) so they can <br />be evaluated for compliance with stormwater management and water body crossings <br />rules. Include inverts, length, slope, size, material, end condition, etc. <br />o Provide delineation of any flowage or drainage easements, or of other property <br />interests dedicated to water management or conveyance. <br />o Please provide full HydroCAD inputs/outputs for 1- or 2-year, 10-year, and 100-year <br />events for the existing and proposed condition. Please also provide HydroCAD (.hcp) <br />electronic files by email for easier/quicker review. <br />o Basin 3 would be impacted by seasonally high groundwater as shown in the borings and <br />would not be suitable for infiltration. Boring 222 indicates a groundwater elevation of <br />950.25+/-. Bottom of basin is 953.0 which is less than the 3 feet of vertical separation <br />required from infiltration surface to groundwater. Additionally, soils are noted as silty <br />clay loams which are noted as having an infiltration rate of 0.06in/hr in the MN <br />Stormwater Manual and are HSG Type D soils. These soils are not suitable for <br />infiltration. <br />o Please use media mix C or D rather than filter topsoil borrow for filtration and <br />infiltration basins so it does not leach phosphorus, per MN Stormwater manual <br />guidance, or provide documentation that filter topsoil borrow will not leach <br />phosphorus. <br />o Remove drainage fabric around underdrain/draintile and underdrain pipes should have <br />a minimum of 3 inches of washed #57 stone above and on each side of the pipe (stone is <br />not required below the pipe). Above the stone, two inches of choking stone is needed to <br />protect the underdrain from blockage. <br />o In HydroCAD, exfiltration should not be discarded. It should be routed to an underdrain <br />and then to the outlet structure. Please update so exfiltration is included in outflow <br />from pond and for peak flow routing. <br />o There must be two feet of vertical separation between the 100-year high water <br />elevation of a waterbody or stormwater practice and the low opening of any structure, <br />unless the structure opening is hydraulically disconnected from the waterbody or <br />practice. Please provide the low opening elevation of nearby existing and proposed <br />structures and high water level of stormwater BMPs. <br />157