3003 W CASINO RD BOEING PARKING LOTS - E 6 2025-07-25

Drainage Report Boeing Everett-E-6 Parking Lot Expansion July 16,2013 to prevent surface flows to and from the existing parking lot. TABLE 1 summarizes the developed site conditions and land cover. 8.4 Stormwater Flow Control Plan Not applicable. The project site is exempt from flow control requirements as it is vested under the previously accepted 1991 Boeing Master Plan. See APPENDIX F for correspondence with the City of Everett approving the exemption. 8.5 Stormwater Treatment Plan Not applicable. The project site is exempt from water quality requirements as it is vested under the previously accepted 1991 Boeing Master Plan. See APPENDIX F for correspondence with the City of Everett approving the exemption. 8.6 Conveyance Analysis Conveyance calculations were completed for the new asphalt parking lot. Results showed that an 8" pipe would provide adequate capacity for the 100-year storm event. However, 12" diameter storm pipe will be used to match the majority of the Boeing conveyance system and provide a factor of safety during high flows. See conveyance calculations in APPENDIX E for the design ' of the onsite conveyance system. 8.7 Operation and Maintenance Plan An Operation and Maintenance Manual was prepared for the proposed catch basins. It is attached in APPENDIX B. I I I I I I I 20130715_Drainage Report_Boeing Everett_Gate E-6 Parking Lot.doc Page 16 I