2401 TAYLOR DR 2022-08-29 - Laserfiche WebLink

6. PRESERVATION OF NATURAL DRAINAGE SYSTEM The runoff from the impervious improvements will be collected and tight lined directly to the toe of the bluff to the north within the BNSF railroad R/W. This is based on the City of Stormwater Management Manual prohibiting infiltration or dispersion of impervious surface runoff within 100 feet of slopes steeper than 20%. The steep bluff slopes found approximately'70`feet north of the building site exceed 35%.'This will slightly change the existing conditions of the site but the outfall from the proposed system will be within 100- feet of Puget Sound. 7._ ON-SITE STORMWATER MANAGEMENT The 'on:site"soils'were found to be fine sandy silt and silty fine sand to a depth of approximately 20 feet below grade. It has been determined that infiltration is not feasible due to the presence of the existing steep slopes/bluff approximately 70 feet north of the proposed SFR. Therefore, a collection/conveyance system has been designed to tightline all proposed hard surface runoff down the slope to the northwest to be discharged at the toe of the slope within the BNSF railroad R/W. 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. 8. SUMMARY This project proposes to construct less than 5,000 sf of new hard surfaces:As a result, the use and land cover for less than 5,000 sf of the site will be converted pervious to impervious surfaces. Stormwater management techniques have been incorporated into the design. Therefore, the stormwaterdesign for this project has met or exceeded all of the applicable Minimum Requirements-5. • Haack-Taylor Drive 19-1112 January 2020 Revised October 2020 Page 9