1130 90TH ST SW 2025-07-29 - Laserfiche WebLink

5. SOURCE CONTROL This project proposes to construct 4 new SFRs on this parcel with 4 new driveways. Per Volume 1 of the City of Everett 2010 Stormwater Management Manual residential development does not require source control. 6. PRESERVATION OF NATURAL DRAINAGE SYSTEM The runoff from the site improvements will be collected by one of four on-site swales. However, 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 Alderwood - Urban Land Complex with a hard pan layer between 20 and 40-inches below grade. Since the parcel size for this project is less than 22,000 sf then on-site swales may be used if infiltration is not feasible. A minimum of three downspout splash blocks are to be used per building, which will drain runoff away from the SFRs and to an adjacent shallow swale which parallels one of the unit lines. Units 1 and 2 will share a swale that runs from north to south between the two units. Units 1, 2 and 3 will share a swale that runs from east to west toward a yard drain and collects the runoff from the swale shared by units 1 and 2. Unit 4 will have its own swale along its southern property line which runs from east to west and drains into a yard drain. Units 3 and 4 will share a swale that runs from east to west and drains into a yard drain. This yard drain collects the runoff from all other on-site yard drains and pipes the runoff to the on-site catch basin. For the two proposed PGIS's on this project the runoff from the driveways will be dispersed using transition zones along the western edges of the new driveways for units 1 and 2, and along the southern edge of the new driveways for units 3 and 4. The dispersed flows 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 PGlS 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. OLYMPIC TERRACE CONDOS 13-0605 June 2013 Page 11