The goal is to reduce the spread of environmental toxins from the port by 90 percent. Between 2016 and 2018, the entire area was dredged, but that was not enough. Now 150,000 square meters of seabed will be covered to meet the requirements.

- Areas where there are still pollutants should be covered with stone crusher. It is in hard-to-reach places between stones and in rocky outcrops, says Bodil Liedberg Jönsson, ordering agent for the decontamination.

First out in Sweden

The method has been widely used in the US and Canada but is new in Sweden. Three different types of gravel and rock will be laid on the seabed. Where the Gotland Ferry has its route, the largest stones will be 50 centimeters in diameter.

The material does not need to be transported far. When the landfill site for the mud masses was built at Storskogen's waste facility, much rock was blown away. It is the blasted pulp that will be used for the coverage.

The trucks will go into gunfire.

"There will be around 5,400 truck trips," says Björn Karlsson, site manager at Peab anlegg AB.

Biggest environmental project

If the plan holds, the seabed should be covered before the summer.

The entire project has cost over half a billion SEK, most of which the state has financed for the Baltic Sea.