Brown and Caldwell, Inc. 9/20/2023

PGSF WMVD Storm and Combined Sewer Design Scope of Work 08-25-2023 9 of 41 Category 2: Sensitive information Category 2: For official use only / disclosure permissible by law. Task 240.001 – Establish Pipe Diameter Minimums Task Objective: Establish minimum required pipe diameters for all A, C, and E conveyance lines to inform Design of pipe rehabilitation selection and trenchless crossing method selection. Task Activities/Approach: This task includes the following activities. Update hydraulic models (sewer and storm) to refine pipe layouts, crossing concepts, diameters according to Facility Plan. Refine regulator structures. Connect to updated PGSF portion of hydraulic model. Develop “Large Pipe” scenario by artificially enlarging all AC&E pipes to have no hydraulic restriction. Run long term simulation to determine true flow regime at key design decision locations. Develop peak flow statistics for modeled flow regime to determine recurrence interval flowrates for AC&E lines. Determine inflection points to identify point of diminishing returns. Iteratively reduce pipe sizes from updated Facility Plan model to determine pipe sizes to pass the 5 year, 10 year, 25 year, 50 Year, and Inflection Point flowrates. Calculate overflow frequency at all PSOs in all 5 scenarios and characterize adverse operational impacts or risk factors associated with each scenario. Coordinate with design team to determine design impacts/opportunities by scenario. Develop presentation materials to workshop the scenarios and design outcomes with the City. Lead Pipe Size Alternatives workshop. Workshop outcome is diameter minimum decisions / scenario decision. Develop Pipe Sizing Criteria Technical Memorandum Task Assumptions Hydraulic model updates to incorporate updated design of PGSF and adjacent vicinity are scoped as part of the PGSF contract Rainfall timeseries used will be the climate modified 33.5-year record developed by BC for the PGSF Facility design Everett Responsibilities • Participate in Pipe Size workshop • Review Pipe Sizing Criteria TM Meetings • Pipe Size Alternatives workshop Work Products • Pipe Size Criteria TM, draft and final Task 240.002 – Establish Initial Pipe Routing and Material Selection Activities/Approach: Review available information to determine the most appropriate location for pipelines, with emphasis on the CO-10 and C0-20 lines, connection points with the PGSF facility, and BNSF crossing. Review installation depths and other requirements to select initial pipeline materials. Task Assumptions: • Publicly available and City of Everett provided GIS/Lidar will be used as basis for routing.