Originally built in 1910, the Maple Leaf Reservoir is the City of Seattleâs largest, holding 60 million gallons of potable water. The Cover project involves the construction a new reservoir from the bottom up. Hermanson Company is responsible for full mechanical (plumbing, piping and HVAC/sheet metal) construction of all piping systems and a new mechanical vault. This project consists of the construction of a dual cell 60 MG cast-in-place reinforced concrete reservoir that includes 30â inlet and outlet pipelines, 42â surge and 36â overflow pipelines, 10â recirculation and 6â wash-down piping, various mechanical vaults (main mechanical vault with isolation valves and recirculation pumps, inlet vault, meter vault and wash-down vault); mechanical vault ventilation systems, modifications to instrumentation and control systems; modifications to existing sodium hypochlorite disinfection systems and acceptance testing and startup. The final stage of construction will involve the covering of the reservoir and the creation of open space which may eventually become a park.