The Municipality of Metropolitan Seattle’s (Metro) Regional Treatment Plant in Renton, Washington (MTPR) was initially constructed in the early 1960s to provide secondary treatment to the communities lying to the east and south of the city of Seattle. Flow was brought to the plant via a gravity interceptor system and, once at the plant, the wastewater was screened, pumped, degritted in preaeration grit removal tanks, settled in primary clarifiers, received secondary treatment via the air activated sludge process, disinfected with chlorine and discharged to the Green River. Specific details on the original plant design are contained in a paper published in the WPCF Journal (Uhte 1963). The plant went on line in June 1965 with an average dry weather design flow of 24 mgd. The plant was designed to be expanded through a series of expansion stages to keep pace with the anticipated growth in the service area.