1815 13TH ST SEATTLE CHILDRENS NORTH CLINIC 2019-07-08

MAGNUSSON KLEMENCIC _ ASSOCIATES ■ I. PROJECT DESCRIPTION This report documents the proposed stormwater and drainage design approach for the Providence Regional Medical Center Everett (PRMCE) North Site project in Everett, Washington. The report has been prepared using the guidelines set forth in the City of Everett Stormwater Management Manual (COESWMM) dated February 2010 by the City of Everett (COE) Surface Water Management. The North Site of PRMCE is located at 1815 13'h Street and is bounded by 13th Street on the south, residential blocks to the north and east, and the Providence Regional Cancer Partnership facility to the west. The 8.98-acre existing site contains PRMCE's Central Utility Plant (CUP) and temporary surface parking. See Figure 1 for a Vicinity Map showing the project location. In preparation for a future clinic facility and associated parking to be constructed in the north third of the site, the North Site project will relocate existing utility infrastructure to avoid conflicts with the new building. The project will also expand the existing parking lot to the west of the CUP to address increasing demands for parking. The existing stormwater detention pond in the northeast corner of the site will ultimately conflict with the clinic facility footprint and so will be replaced with an underground detention vault east of the CUP. The project limits of work are shown on the Project Site Plan included as Figure 2. Approximately 2.77 acres will be disturbed for clearing, grading, excavation, etc., for the North Site project, with approximately 6,300 bank cubic yards of cut and 2,600 bank cubic yards of fill required to establish finish grade, including earthwork required for the detention vault excavation and installation. Because the future clinic facility development will tie into the on-site conveyance system and detention facility designed and installed as part of the North Site project, this report will address the flow control and conveyance requirements for both the North Site development and the future clinic facility. The total increase of impervious area for the North Site project and the future clinic is approximately 4.58 acres. The site development and utility work for the clinic will be under a separate permit. II. SITE ASSESSMENT See Appendix A for a copy of the site survey completed by Bush, Roed, & Hitchings, Inc. on May 3, 2016. The survey shows existing contour elevations for the site as well as existing surface features and utility infrastructure. Potholing was also performed on select utilities to determine depth of bury. TOPOGRAPHY Generally the site slopes inwards from the northwest and northeast corners, and then maintains a steady slope south to the lowest point on the site, near the access driveway at the middle of the southern property limits along 13' Street. DRAINAGE There are two means of discharging existing drainage on the site, with the extent of each generally matching the limits of the two previous construction projects on the site: the CUP construction in the western half of the site (referred to herein as the CUP project) and the more recent construction of temporary parking in the eastern half (referred to herein as the CUP Parking project). Storm Drainage Report 1 Providence Regional Medical Center Everett North Site, Everett, Washington