The Blominmäki sewage treatment plant is being built in Espoo, Finland, with a target completion date of 2021. It represents the most expensive investment of the ever, with a total cost that could be as high as 392 million Euros. It is the second most expensive infrastructure project in the Helsinki Metropolitan Area, behind the coming extension of the Western Metro. The plant will clean sewage from some 400,000 local residents from Espoo, Kauniainen, Vihti, Siuntio and western Vantaa. In the future, its operations could be enlarged, so that it could process the sewage of a million residents.