The city of Joensuu in the eastern part of Finland is transforming an old contaminated sawmill area near the city centre into an up-to-date housing district. Before the building can start, the whole area must be thoroughly restored after more than a century of heavy industrial use.

Joensuu which means "mouth of a river" is a lively city of about 75,000 people, located 450 km north-east of Helsinki. From 1871 until 1988, a sawmill was operated on the banks of the river Pielis close to the city centre in an area called Penttil?. After a century of industrial use, the soil and storage bay at the Penttil? area had become severely contaminated with heavy metals and other toxic materials.

The city had bought Penttil? in 2008 and was planning to turn the area into a modern, eco-friendly housing district for 3,000-4,000 residents during the next 20 years. But the area had to be thoroughly cleaned first.

The total restoration cost rose to about Euro 21 million, being one of the biggest restoration projects ever to be carried out in Finland. The name of the project became "a dream at the river mouth".

Penttil? district is altogether 40 hectare in size and more than 500,000 cu m of soil was to be cleaned.

The old storage bay right next to the river had been kept open during the winters by directing the flue gases from the near by plant to the bay. This inevitably caused the accumulation of vast amounts of heavy metals in the bottom sediments. The size of the bay is about 3 hectare and the depth varies from 2 to 4 m. It was the most polluted spot in the whole sawmill area and the cleaning of the bay was considered to be the most challenging part of the whole restoration project.

The bay is shallow and hard to reach with traditional dredging machinery so after thorough trials, the versatile Watermaster dredger was chosen to be the best solution for the site. Watermaster is a Finnish-made serially produced versatile dredger, that can do suction-
and backhoe-dredging and even pile driving work. Watermaster can "walk" in and out of water without crane assistance and it moves independently in water as well, minimising the need of extra machinery and labour and is thus a very cost-effective.

The contractor has operated all the previous Watermaster generations as well but is now using the latest model - Classic IV, the fourth generation of the original Watermaster concept. He is very happy with the new Classic IV as it offers more depth, greater boom and stabilizer forces and cabin LX.

Watermaster has suction dredged vast amount of contaminated sediments from the bay during 2009-11. The material is pumped into geotextile tubes to separate the sediments from the water. About 30 geotubes have been used at the site so far (50 m long and 9 m wide approx). Sediments are left to dry for about a year and will then be transported for further processing to the nearby waste treatment plant. A small marina will be built to the storage bay area later on.

The cleaning of the whole area is to be completed during 2011 and the building phase can begin in 2012. Penttil? should be receiving its first new residents in 2013 but new buildings will keep rising during the next two decades.

By the completion of the project, Penttil? will have been transformed from an industrial wasteland into a modern, verdant and desirable new residential area, which will undoubtedly attract new residents to live at the "mouth of the river".

Plan

2009-2011: Area restoration
2010-2012: Building the infrastructure
2012: Building of the apartments begins
2013: First new residents
2014: New bridge to the city for pedestrians
2015: The small Marina to be completed
2030: The whole project to be completed