CHS Engineers LLC 5/4/2020 - Laserfiche WebLink

EXHIBIT A City of Everett Lift Station #15 and Force Main Siting Evaluation and Pre-Design Scope of Work March 30, 2020 Introduction The City of Everett owns and operates a domestic wastewater"lift station" immediately adjacent to an existing City-owned bridge along W. Mukilteo Blvd. The station is situated on the north side of the road, on a steep bank above Edgewater Creek, immediately west of Shore Ave. The station is partially on easement and partially in the City right of way. The station is west of the City's Edgewater Park. The park includes limited parking immediately east of the station/west of the park, a large lawn and sport and play areas. Immediately east of the park is another City-owned property with lawn and trees. The City intends to remodel the park in the near future. The station consists of a cast-in-place concrete structure configured with a control room above a dosing tank and a full depth outlet box. The tributary area is served by a separated sanitary sewer collection system, extending east along Shore Ave. and east along W. Mukilteo Blvd. The service area includes approximately 413 single family homes east and southeast of the station. The collector along Shore Ave. is approximately 29 feet deep between the park and the station. Flow from those collectors join in a manhole with bypass pipe in Shore Ave. Gravity flow enters the dosing tank or bypassed flow is directed to the outlet box. Wastewater is conveyed away from the outlet box by gravity discharge. The control room is accessible from stairs from street level and through a side door, or through a roof hatch. The dosing tank is accessible from the control room through a manhole cover in the floor. The outlet box is accessible only through a manhole. The "lift station" was originally designed as a flush tank to receive and periodically discharge a large volume of wastewater by gravity to the downstream conveyance system. The "flush" function may have been disabled since installation so that now the dosing tank and/or outlet box simply function as a flow-through wet well. The station has been modified with fencing for controlled access and SCADA and communication equipment for remote monitoring. A slab has been added to support a polyethylene tank for onsite storage of Bioxide®. This calcium nitrate solution is dosed to the wastewater for odor and corrosion management in the downstream conveyance system. The discharge from this station is conveyed in piping north along the ravine to a City interceptor flowing east/northeast along the shoreline of Possession Sound (Mukilteo Beach Interceptor). The interceptor also receives flow from a small pump and 2" force main serving the office at the Port of Everett pier, located to the west along the shoreline. The City's interceptor is in unknown condition and it would be very challenging to replace in the shoreline environment. The City is planning a project to replace the bridge and that project will require additional space for construction and temporary facilities and will likely require removal of the existing station. Given the concerns about the condition and cost of replacement of the shoreline interceptor and anticipated impacts from the bridge replacement project, the City has identified a project CHS Engineers, LLC Page 1 of 5