2410 WALNUT ST 2018-01-02 MF Import

6. PRESERVATION OF NATURAL DRAINAGE SYSTEM The runoff from the NPGIS improvements will be dispersed as sheet flow over amended soils By not grading or compacting the majority of the pervious surfaces to remain after construction in the area of disturbance a maximum amount of site runoff from the developed project will be absorbed and infiltrated into the existing on -site soils This will mimic the existing conditions by maintaining the existing direction and condition of flow from this site. 7. ON -SITE STORMWATER MANAGEMENT The soils for this project were found to be loam with a water table depth between 18 and 36 inches below grade Since the parcel size for this project is less than 22,000 sf then dispersion of the NPGIS may be used if infiltration is not feasible. Dispersion of the NPGIS will be done using downspout splash blocks. The proposed roof surfaces total approximately 2,520 sf The proposed roof surfaces for the proposed SFR totals approximately 1,467 sf and a minimum of three downspout splash blocks are required. The proposed roof surfaces for the proposed detached garage totals approximately 1,053 sf and a minimum of two 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 for the proposed SFR will disperse runoff east toward a shallow swale to be located along the northern property line The splash blocks for the proposed detached garage will disperse runoff east toward a shallow swale to be located along the southern property line. The swales will drain east. as it makes their way towards the road. A total of approximately 710 sf of PGIS is proposed for this project The runoff generated by the impervious driveway surfaces will be dispersed to the north side of the property and be collected by a shallow swale to be located along the northern property line. The dispersed flow will pass over existing landscaping or amended soils prior to leaving the site or naturally infiltration 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. 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 locations of the soil amendments and additional details. Refer to Appendix A for Soil amendment quantity calculation. 8. SUMMARY This project proposes to construct less than 4,000 sf of new impervious surfaces including driveways and roof areas. As a result, the use and land cover for less than 4,000 sf of the site will be converted from pervious to impervious surfaces. On -site stormwater management techniques have been incorporated into the design to mitigate for this land conversion. In addition, based on the proposed improvements for the site drainage design the post developed runoff from the site is expected to increase slightly from the existing system Therefore, the stormwaler design for this project has met or exceeded all of the applicable Minimum Requirements 1-5. Walnut SFR 14-0420 May 2014 age 9