3003 W CASINO RD BLDG 40-58 2025-07-25

I Project Description The proposed project consists of a new 40-58 building which will be located directly east of the existing 40-56 building. The existing 40-83, 40-84, and 40-85 buildings and their associated infrastructure will be demolished to accommodate the proposed 40-58 building. The construction will include new underground utilities and site infrastructure, as well as new paved apron areas to support the new building. Additionally, the existing Boeing Perimeter Road will be re-routed to the north to provide Iadditional clearance for the new building. A meeting was held with City of Everett Public Works on April 3, 2014 to discuss the stormwater design for the proposed 40-58 building. The conclusion from this meeting was that the existing stormwater management systems in place had adequate capacity for the new project, and that the stormwater design for the new building should match the existing outfalls and permitted coverages as best as possible. This is to be accomplished by continuing to maintain existing basin boundaries and coverages I to the best degree possible and continuing to send sub-basin flows to their existing outfall locations (see meeting minutes in appendix). It is the intent of this report, with supporting exhibits and drawings, to demonstrate the proposed design meets and exceeds these requirements. Existing Condition Summary The existing North Boeing Everett Campus is broken into two large basins draining to Japanese Gulch and Powder Mill Gulch according to the Technical Appendix C Surface Water Study from the 1991 EIS Report by CH2M Hill (1991 EIS Report). The 40-58 building improvements impact three outfalls that ultimately drain to Powder Mill Gulch: (See Exhibit 1 for Overall Basin Map) - Powder Mill Gulch Detention Pond - West Detention Pond (Fluke Pond B) via bio-swales and wetland o A Portion of this basin runoff is infiltrated into the ground via underdrain - Fluke Pond A via bio-swale and wetland The 1991 EIS Report assigned contributing runoff areas and impervious coverage to each of the individual sub-basins. Subsequent to this report, the Boeing Office Complex improvements associated with the 40-87 and 40-88 buildings revised the permitted drainage outfalls, affecting a portion of the 111 1991 EIS Report sub-basins. These improvements predominantly affected sub-basin 88 (split into 88A and 88B), sub-basin 79, and sub-basin 80 from the 1991 EIS Report. Because these basin areas and impervious coverages have not been updated to reflect these improvements, Sub-basin A, Sub-basin I B, Sub-basin C and Sub-basin D have been created to analyze impact to the existing conditions. It is assumed that the existing conditions today do not substantially differ from the permitted design of the Boeing Office Project. As such, the existing conditions were considered as the baseline for comparison I of these affected sub-basins and the 1991 EIS Report sub-basins. The following table summarizes the revisions made to the 1991 EIS Report sub-basins and the new sub-basins: I 1 1 I