3003 W CASINO RD BOEING STORMWATER MGT SYSTEM 2023-12-28

K File:Boeing Everett SSA_noPS_11-16-20.spf Ke n n ed y J e n ks Job Number: 2096009*01 Date: March 5,2021 \\KJC\KJC-Root\KJ-Office\FWY\Data\Projects\2020\2096009.00 Boeing Everett SW Treatment\10-Design\10.05-Calcs\2-Civil\SSA Model\[SSA Model Documentation gravity concept.xlsx]Assumptions CLIENT: Boeing Comercial Airplanes/ Boeing Everett Facility JOB NO.: 2096009*01 DATE: March 5, 2021 PROJECT: Stormwater Improvements ENGINEER: Jenny Mital DESCRIPTION: SSA Model Documentation -Assumptions CHECKER: Design Assumptions Purpose: Confirm that the gravity storm drain system is adequately designed to deliver 24cfs to the EMF basin, and a total flow of up to 49cfs to the stilling basin. 2020 Survey Horizontal Datum: NAD 83(91) 2020 Survey Vertical Datum: NGVD 29 General Site Information: Size: 700 acres approx. Watershed: Boeing Everett Facility Offsite run-on: Yes, included in the above acreage Storage Design Criteria: Minimum Freeboard n/a ft Maximum Ponding Depth n/a inches Model Assumptions: Design Storm: N/A Existing pipe sizes, lengths, and inverts were set based on survey data by DHA. Proposed pipe and structure invert elevations and rims are set based on survey data and the IFC submittal plans. o EMF basin invert elevations were set to 345.5ft instead of the actual elevation of 346ft. This was done to avoid a negative pipe slope modeling error in SSA. o T-structures in the flow splitter manholes and EMF outlet manholes were not modeled. A dummy node and conveyance was added upstream of the detention basin to increase model stability. Inflows are set using baseline flows in each basin and not by using a storm. The interaction between the two basins (SB & DB) is not modeled as there are currently not issues with how the basins interact. The initial model set a baseflow of 8 CFS entering the sedimentation basin outlet riser. This was then changed to 4cfs because that was the maximum that pipe could convey. The boundary conditions at the wetland are set to 340.25 based on expected conditions. The oulet boundary condition at the stilling basin is set to normal depth. Weirs in manholes are modeled as link between the manhole and a dummy node set to the same elevations as the manhole itself. A diversion node cannot be used with the necessary hydrodynamic routing method. The treatment system is sized to treat 24-30 cfs flow at a minimum of 18"/hr design infiltration rate. The media flowrate is limited to 15 cfs per basin in SSA. Minor losses are set to the most conservative value recommended by the SSA documentation. Losses for CDS units are not stated in the documentation, so the highest value, 1.0, was used in the model. Dead storage of the overflow chamber is dictated by the downstream outlet elevation