1822 CHESTNUT ST 2017-01-13 - Laserfiche WebLink

7. ON-SITE STORMWATER MANAGEMENT The soils for this project were found to be sandy loam with a water table depth between 18 and 36 inches below grade. Since the soils are ciassified as till and the water table is conceivabiy less than 3 feet below grade, dispersion of the NPGIS may be used since infiltration is not feasible. Dispersion of the NPGIS will be done using downspout splash blocks. The proposed roof surfaces for the site total approximately 1,622 sf and a minimum of three downspout splash blocks are required. Each downspout will not be allowed to collect runoff from more than 700 sf of roof area. The splash blocks will disperse runoff away from the proposed SFR to the north toward a shallow swale. Runoff from the proposed SFR will sheet flow to a shallow swale proposed near the center of the parcel. The shallow swale will direct runoff in the easterly direction toward the eastern property line. The shallow swale will allow for some natural infiltration on-site and maximize vegetated flow paths before flows leave the site. This will aid in preventing runoff from draining onto neighboring downslope properties. Any excess runoff that is not infiltrated from the shallow swales shall be collected by a catch basin. This catch basin shall convey excess runoff to the street gutter line and connect to a bubble-up catch basin energy dissipater, proposed within the right-of-way of Chestnut St. A total of approximately 780 sf of PGIS is proposed for the site. The runoff generated by the proposed impervious driveway surfaces will be dispersed toward the north. The dispersed flow will pass over existing landscaping or amended soils prior to leaving the site or naturally infiltrating on-site. This project does not propose to construct more than 5,000 sf of PGIS so it is exempt from any water quality treatment systems per Minimum Requirement 6. Any excess runoff not infiltrated on-site shall be collected by the proposed conveyance system mentioned above. 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 DOE BMP T.5.13. Please refer to the engineering plans for the basic soil amendment notes and additional details. Refer to Appendix A for Soil amendment quantity calculation. Haack Chestnut SFR 15-0118 October 2015 Page 10