2413 74TH ST SE 2025-08-20 - Laserfiche WebLink

As documented in Section 1 of this report this project is required to meet Minimum Requirements 1-5. As a result, this project is required to use the On -Site Stormwater Management BMP's from 2019 DOE SWMMWW. Per the DOE SWMMWW, the BMP's must be evaluated in the order they are listed. BMP's for roofs: 1. Full Dispersion: Not feasible due to the 65:35 requirement. 2. Downspout Infiltration Systems: As mentioned in Section 2, the soils were found to be dark brown sandy loam with hardpan encountered at a depth of 6-35 inches below grade. The minimum required vertical separation cannot be provided. Due to the soil conditions of the site, infiltration is not feasible for this project. 3. Rain Gardens and Bioretention: Similar to Downspout Infiltration systems, the soil conditions of the site make rain gardens and bioretention not feasible for this project. 4. Downspout Dispersion Systems: The proposed roof area for the SFR totals 2,014 sf. Dispersion of the NPGHS will be done using splash blocks. Three (3) splash blocks are proposed. Each downspout splash block will not be allowed to collect runoff from more than 700 sf of roof area and will have a minimum 50-foot flow path over vegetated surfaces before the flows leave the site. BMP's for other surfaces: 1. Full Dispersion: Not feasible due to the 65:35 requirement. 2. Rain Gardens and Bioretention: Similar to Downspout Infiltration systems, the soil conditions of the site make rain gardens and bioretention not feasible for this project. 3. Sheet Flow Dispersion: This project will disperse runoff from the concrete driveway by sheet flowing to the east. Finally, any area of the site not proposed to be covered with impervious surfaces but graded or compacted will be treated to meet the criteria for BMP T5.13. Please refer to the engineering plans for basic soil amendment notes. Haack — 74th 22-0807 September 2022 Page 9