3531 NORTON AVE 2022-02-23 - Laserfiche WebLink

7. ON-SITE STORMWATER MANAGEMENT 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 Chapter 12 of Volume III in the 2010 COE SWMM. Per the COE SWMM the BMP's must be evaluated in the order they are listed. BMP's for Roof Runoff: 1. BMP 12.30 On-site infiltration areas: As previously mentioned in this report,the on-site soils were found to be loamy fine sand with mottling found at 50-55 inches below grade. However,the entire east portion of the site contains steep slopes at 34%. Since the slopes are greater than 25%, infiltration is not feasible. 2. Downspout Dispersion Systems: As previously mentioned, this site contains slopes at 34%. Per the stormwater manual, runoff should not be dispersed over slopes greater than 15%. Therefore, dispersion BMP's are not feasible for this site. 3. Perforated Stub-out Connections Due to the fact that infiltration and dispersion BMP's are both infeasible for this site, a perforated stub-out connection may be used. Runoff from the proposed roof surfaces should be tightlined via a solid pipe to the toe of the steep slopes on the east side of the project site. Runoff should then be directed to the existing stormwater system within the right-of-way. This will be accomplished by the use of a perforated section of pipe. The perforated stub-out connection should be connected to the existing stormwater system within the right-of-way of Grand Ave. BMP's for other hard surfaces: No other hard surfaces proposed for this project. Proposed Pervious Areas: 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 12.20. Please refer to the engineering plans for basic soil amendment notes. Grandview Ave Duplex 18-1001 January 2019 -Pag9 1n1 \5