Brown and Caldwell, Inc. 9/20/2023

PGSF WMVD Storm and Combined Sewer Design Scope of Work 08-25-2023 8 of 41 Category 2: Sensitive information Category 2: For official use only / disclosure permissible by law. 5.Handheld thickness measurement results 6. Information for use in Phase 250. Phase 230 – Stormwater Pretreatment Analysis Objective: To determine locations of stormwater pretreatment needs Activities/Approach: Continue completed work to date, from other BC contract, to continue the stormwater pretreatment needs and locations. Preform field investigation of three proposed pretreatment locations along Rucker Ave between 14th and 16th streets and along 15th St between Hoyt and Colby avenues for three locations to pretreat stormwater in the Sewer M basin. Perform measure downs at maintenance holes. Coordinate proposed location of pretreatment unit along CO20 alignment during Phase 240 Technical Refinement. Update storm hydraulic model to reflect most recent field investigation, survey, as-built or GIS data for rim and invert elevations of storm system pipe network at and upstream of proposed pretreatment unit locations. Perform hydraulic simulations for future conditions which include build out impervious conditions, separated stormwater in planned separated system, and climate-adjusted precipitation). Confirm CDS unit sizing based on the 6-month flow rate at the proposed location and flow velocity rates upstream of the location. Develop presentation materials to workshop the scenarios and design outcomes with the City. Lead Pretreatment Unity Alternatives workshop. Workshop outcome is unit location and sizing/scenario decision. Develop Pretreatment Unit Location and Sizing Technical Memorandum. Task Assumptions Refinements to stormwater treatment system design as a result of stormwater hydraulic model updates of pretreatment units are scoped as part of the PGSF contract. Rainfall timeseries used will be the climate-adjusted 33.5-year record developed by BC for the PGSF Facility design Everett Responsibilities •Participate in field investigation efforts. •Participate in Pretreatment Unit workshop •Review Pretreatment Unit Location and Sizing TM Meetings •Pretreatment Unit workshop Work Products •Pretreatment Unit Location and Sizing TM, draft and final Phase 240 – Technical Refinement Phase Objective Establish the basis for project elements prior to proceeding into the basis of design phase. This includes establishing minimum pipe diameter sizes and identifying routing analysis to identify pipe locations.