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HomeMy WebLinkAbout006 Stormwater Dishcarge Memo cushingterrell.com March 24, 2023 Suzanne Ryan, PE City of Bozeman 20 E. Olive Street Bozeman, MT 59715 RE: Berkshire Heights Bozeman Parcel Distribution Stormwater System Requirements Mrs. Ryan, The purpose of this memo is to address city code Section 38.410.070 – Municipal water, sanitary sewer and storm sewer systems. The proposed project plans to manage stormwater runoff using existing infrastructure on the predeveloped plot. Current Infrastructure Referencing the discharge report performed by C & H Engineering and Surveying INC. in the previous phase of this development, the current stormwater management plan consists of retention and underground detention facilities in the northwest corner of the plot. The sizing of these facilities was based on estimations in hardscape and landscape areas in future phases of development in the area. The area in which our design takes place is Lot 4, containing a total area of 13,587 SF. Within this area, it was previously estimated that there would approximately be 3762 SF of pervious/landscape area and 9825 SF of impervious/hardscape area, resulting in a weighted runoff coefficient of 0.742. The current site design has a pervious area of 4289 SF and an impervious area of 9298 SF, resulting in a weighted runoff coefficient of 0.713. Since the current coefficient is less than the estimated value, there will be less runoff coming from this site. Since there will be less runoff, the current stormwater facilities will be appropriate for future stormwater treatment. Please reference the attached stormwater exhibit for more information. Sincerely, Adam Schlegel, PE LOT 4PROPOSED BUILDINGFOOTPRINT = 4,929 SFwmwmwmwmwmwmss WVssssfofowmwmwm wm wm wmgasgas BPBPBPBPBPBPBPwmwmss DRAWN BY |REVISIONS©| ALL RIGHTS RESERVEDCHECKED BY |®BHHS BOZEMAN OFFICE BERKSHIRE HATHAWAY HOME SERVICESSITE PLAN SUBMITTAL03.24.20232023NORTH0102040SCALE: 1" = 20'LAND COVERAGETYPEAREA (SF/AC)AREA (%)RUNOFFCOEFFICIENTIMPERVIOUS9298/0.21680.95PERVIOUS4289/0.10320.20TOTAL13587/0.31100WEIGHTEDCOEFFICIENT:0.713IMPERVIOUS AREAPERVIOUS AREASTORMEXHIBIT1STORM EXHIBIT