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MEMORANDUM TBPLS Firm No. 10074302 Date: August 31, 2021 Re: Bremer Bank - Stormwater Management Summary File 0026999.00 To: Victoria Perbix, Interstate Development From: Dan Parks Below is a summary of the stormwater management system designed for the new Bremer Bank facility in St. Anthony, MN. •The proposed 0.91-acre Bremer Bank site is presently vacant but has previously been occupied by buildings and a parking lot. •The native soils on the site are not sandy, but largely cohesive clayey-type materials that do not infiltrate well. •The proposed bank use will convert the present grassy lot to approximately 75% impervious. •Due to the required development density for the bank, it is not feasible to incorporate open- water ponding areas into the project design and a below-ground stormwater vaulting system will be used instead. The stormwater vault will temporarily store runoff and limit stormwater discharge rates from the site to their current runoff rates. It will also provide water quality improvement. •Stormwater from the proposed building and parking lot will directly runoff into the storm sewer and from there into the below-ground vault. When the vault reaches capacity, it will discharge east by pipe into the city storm sewer system in the alley abutting the property. •The below-ground vault will incorporate perforated pipes (or similar system) and be surrounded by an aggregate material with large void spaces. •The vaulting system is typically inspected on an annual basis, and collected sediment is removed as needed. •A more complete analysis of the proposed stormwater system is included in the Stormwater Management Plan prepared with the city site development application. 68