New remediation method used in Ropsten

Remediating land in Stockholm Royal Seaport is necessary to build in and develop the district. There are several different ways to do this, and in conjunction with remediating land in Ropsten a new remediation method for Sweden is being tested.

After more than 100 years of industrial activity and gas production in the Gasverket area, it is necessary to remediate land, groundwater and sediment before we can start building homes, pre-schools, business premises, parks and squares. The ground is partly an old lake bed with thick layers of clay. When gas was produced in the area, filling masses were laid on the lakebed to expand the area available for industrial activity. Today, the clay and filling masses are contaminated by, among other things, tar oils, benzene and heavy metals. In addition to being remediated, the land also needs to be reinforced to avoid subsidence damage when it is built on.

Remediating and stabilising land in situ

The filling masses are transported from the site. The clay, which is up to 15 metres thick in places, must be remediated and reinforced before it is built on. To solve these two problems, the project uses a completely new method for land remediation in Sweden, which stabilises the clay geotechnically at the same time as chemicals are added so that the pollutants are broken down through chemical oxidation. An oxidizing agent in liquid or gaseous form is added to the contaminated area, and the oxidizing agent converts soil or groundwater contamination into less harmful environmental and health metabolites. In complete oxidation, carbon dioxide and water are formed as final products. The method is known as ISS–ISCO: In Situ Stabilisation and Solidification – In Situ Chemical Oxidation. “In situ” is Latin for “in place”.

Stabilisation is done with a 130-tonne machine fitted with a mixing beater two metres in diameter. The mixing beater stirs the clay with cement and an oxidizing agent and in this way the clay is stabilised and impurities are broken down at the same time.

Remediating the clay in situ reduces the number of transports that would otherwise have been needed to excavate it and remove it from the site. Land remediation reduces the spread of pollution to Lilla Värtan and will make it possible to live in the area free from health risks. Assessments and tests have been carried out for many years to determine which remediation measures are suitable, and we are delighted that this work is underway.

Land remediation in Ropsten began in 2020 and is expected to take two to three years. An environmental control organisation is on site daily to take samples to ensure that our measurable soil and groundwater goals for the project are achieved. Measurements are also taken to check odours and pollution levels in the air. Environmental monitoring of groundwater will continue for several years after remediation is completed.