Land remediation and bulk materials management
Stockholm Royal Seaport is being developed in a former industrial and port area, including a former gasworks. This industrial activity has resulted in pollutants such as tar, petroleum hydrocarbons, and heavy metals in the soil, and contaminated bottom sediments.
Reduced costs and fewer transports with local soil remediation
A total of 220,000 m3 of contaminated soil needs to be remediated for the Kolkajen and Ropsten phases. Instead of transporting all the soil ti a treatment facility, it is being remediated on site. With new technology that stabilises the soil while it is treated, 35,000 m3 of clay has been remediated and reinforced on site and 51,000 m3 of moraine under the clay has been remediated using chemical oxidation. 63,000 m3 of highly contaminated soil has been transported to an approved landfill. More than 50% of the costs have been saved and also 12,000 truck transports.
- Around one third of the area has been remediated.
- 40% of rock and excavation materials have been reused, amounting to 900,000 tonnes.
Land remediation and management
The development of Stockholm Royal Seaport has required the treatment of land and water contamination in former industrial areas. The City of Stockholm therefore conducts land remediation work as the area is developed. The City has a high level of ambition for its sustainability work in Stockholm Royal Seaport, both in terms of remediating land in situ rather than excavating soil for transport, and by continuously streamlining transports of excavated soil as much as possible.
Work has been conducted to develop new environmental and health risk assessments for upcoming development phases. These assessments provide insights into the risks posed to people and the environment by current contamination levels. Improved knowledge base and new calculation models in government requirements have made updated assessments possible.
The Kolkajen and Ropsten areas have extensive contamination due to previous handling of by-products from gas production. The main contaminants are tar and benzene that have seeped into the ground. Extensive remediation has been underway at the site since 2019. The clay, which is up to 15 metres deep, has been both remediated and strengthened. Calcium cement pillars have been created using a two-meter wide "whisk", and persulfate has been added to break down tar pockets in the clay, a new technique never used in Sweden before. Under the clay is friction soil (moraine) that has also been treated with persulfate, which has been injected through pipes in the ground. Regular testing ensures that levels of contaminants have decreased. If levels have not reached the required levels, the treatment is repeated.
Sofia Billersjö, Land Environment Specialist, Fredrik Bergman, Implementation Manager and Christina Salmhofer, Sustainability Strategist at Stockholm City Development Administration explain the process of remediating land, sorting the contaminated soil and rocks in Ropsten and why the green and blue structures in the public spaces play an important role. Andreas Huss, architect and resident, shares his experience living in the area.
Source: Carbon Neutral Cities Alliance
Mass Consolidation Centre
Excavation and site preparation generates rock and soil that needs to be handled. A process that usually involves heavy transportation and carbon dioxide emissions. A local crushing station was established, making it possible to crush remediated rock on site. Materials with a mixture of rock and soil could, however, not be taken care of and utilised. To streamline the management and thus avoid unnecessary transportation, a Mass Consolidation Centre was developed from 2016 to 2019 - a local facility for management of excavated materials where the materials are sorted for local use, sold to external projects or transported away from the area. The Mass Consolidation Centre is also used for handling bulk materials from external projects around Stocholm.
The City takes both rock from construction and soil to the centre contributing to a larger amount of reuse and reduces both the climate impact of the construction and the City's costs. Since all sorting of the masses takes place inside a hall building, it also results in less dust and noise for neighbors.
To improve the sorting of soil, the Mass Consolidation Centre has received funding from the City´s climate investment funds for a combined dry and wet screening facility that can increase the recycling rate from 35 per cent to 75 per cent. The current dry screening separates out coarser fractions, but the new wet screening makes it possible to reuse everything larger than 1mm. The City, together with Ports of Stockholm, has received an environmental permit for bulk handling and handling of hazardous waste centre, which will be used when the wet screening facility is completed.
Cooperation has been developed with the Stockholm Region and the administration for the extended subway by accepting material from the expansion for local reuse. As of 2022, rock from the metro construction is received by water via barge. This relieves Stockholm's inner city road network from heavy transport by truck.
Key events in 2022
- Excavation remediation in Värtahamnen and purification of drainage water during the Ropsten tunnel construction has commenced.
- Reuse of rock materials and purification of drainage water at Gasklocka 2 completed.
- On site soil and groundwater remediation of Kolkajen and Ropsten.
- Construction of a new combined dry and wet screening facility in the Mass Consolidation Centre. The centre has handled 321,000 tonnes of rock and excavation materials, of which 70,000 tonnes came from the Stockholm Royal Seaport development and the rest from external projects, with the largest proportion, 171,000 tonnes, coming from the construction of the metro.
- Of the handled masses, 180,000 tonnes of rock materials in various fractions have been produced. 36,000 tonnes of material had to be sent to landfill, mainly contaminated soil.
- Co-operation with Region Stockholm to increase the reuse of bulk materials in conjunction with the extending of the metro was initiated.
- New environmental and health risk assessments were carried out for upcoming development phases.
Achievements for 3. Land remediation and bulk materials management
3.1 Reduce amounts of waste
To date 29% of the area has been remediated.
900,000 tonnes of excavated materials have been reused in Stockholm Royal Seaport, which means that approximately 60,000 round-trip journeys have been avoided.
in Stockholm Royal Seaport is 91 kg per person/year (2022). Residual waste was 104 kg per person/year (2021).
Pop-up Reuse has so far been visited by 20,700 people. 12,300 items were given new owners, thus 6.2 tonnes have been recycled.
The amount of construction waste in new construction varies greatly between the developers; from 25 to 158 kg/m² GFA.