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Ms. Katie Larsen <br />10/29/2024 <br />Page 3 <br />3. Provide an equalization pipe or channel between the existing City stormwater basin <br />and proposed infiltration basin at the 100-yr HWL (906.3). <br />4. Pipe storage for infiltration is not allowed for water quality volume or rate control. <br />Nonperforated pipes must be used for storm sewer conveyance. <br />5. An outlet control structure will be needed for the southern infiltration basin based on <br />proposed RCWD rule changes due to go into effect by the end of 2024. <br />a. At the very least, permanent stabilization is needed along the overflow path <br />to reduce the likelihood of large-scale erosion in major storm events. <br />6. Soil borings indicate significant amounts of SM soils, meaning design infiltration rates <br />should be 0.45 in/hr consistent with RCWD and MPCA standards. <br />7. In -situ infiltration rate testing will be needed during or after construction to confirm <br />designed rates are achievable. <br />a. Testing before construction can be used to demonstrate infiltration rates <br />above the 0.45 in/hr standard. <br />8. Both infiltration basins must be able to demonstrate they meet 48-hour drawdown <br />requirements. <br />9. The lowest -floor elevation of all buildings must be specified to ensure compliance <br />with infiltration basin freeboard requirements (basin bottom must be at or below <br />lowest -floor elevation). <br />a. This is especially relevant for the potential oil change pit in the Valvoline <br />building. <br />10. Show roof drain routing. Tie into storm sewer at or upstream of a sumped structure to <br />provide pretreatment of roof runoff. <br />11. The Marketplace Drive roadway and existing stormwater basin, including offsite <br />tributary drainage, must be included in the HydroCAD model to understand all flows <br />throughout the site. <br />12. HydroCAD runoff should be set to "Calculate separate pervious/impervious runoff <br />(SBUH weighting)" for most accurate runoff results. <br />13. Proposed impervious should be entered as paved parking and roof as there is a mix <br />of both. <br />14. Existing and proposed models should route to a Link node to calculate total offsite <br />flows. <br />15. Confirm drainage area delineations match site grading, some areas on the perimeter <br />of the sites do not appear possible to route to proposed stormwater basins as <br />indicated in HydroCAD. <br />16. For modeling of outflow rates and HWLs, exfiltration is not allowed in HydroCAD to <br />conservatively design assuming basin infiltration capacity is lost in the future. <br />• Water Supply <br />Java Properties - Lino Retail 2.0 Engineering Review <br />