Over the last years many questions about dangerous substances in bedrock have reached the geological survey of Sweden – mainly from Stockholm but also from other areas of Sweden. The questions concern mostly tunnel muck generated from land preparation areas or infrastructure projects. Several different dangerous elements have been found in the cases reported below, both from whole rock analysis of rock samples and from water analysis. The results exceed either the national limits or the recommended limits of the European Commission.

Material supply in Stockholm and Sweden
Approximately 40 to 80 million tons of aggregates are generated each year from tunnel constructions etc., i.e. tunnel muck. A lot of the masses generated from construction sites are directly recycled on site, but some material must be stockpiled at the local, nearby quarry or at a landfill. The value of the excavated materials from all construction sites in Sweden, such as tunnel muck, is estimated to 0.1 to 0.3 billion euros each year. Estimated costs of the disposal of all material from construction sites to landfill, approximately 40 million tons, exceeds 2 billion euros. It is very important to re-use most of the leftover materials from construction projects.

Geological background of Stockholm and threshold limit value for sulfides
The bedrock of the Stockholm area at many places is dominated by sedimentary gneisses. The gneisses are believed to origin from Precambrian greywackes which sometimes contain sulfides.
Sulfides contain metal ions, normally iron, and if these are in higher quantities in sensitive areas, they can lower the pH levels in surrounding water areas. Sometimes the sulfide minerals may contain dangerous substances, i.e. arsenic, lead, copper, or zinc. Some mafic rocks, like gabbro or diorite may also contain higher levels of dangerous substances.

SGU has not been mapping the geochemistry of the local bedrock in the Stockholm area. Most mapping projects done in the Stockholm area have been performed before 2000. When rock samples have been collected mainly the major elements have been analyzed (Si, Al, Fe, Mg, Ca, Na, K, Ti, P, Mn), very few whole-rock-analyses have been performed.
The Swedish recommended threshold limit values of waste material were laid down after the mapping of the Stockholm region was completed. SGU made an investigation of the water areas north of Stockholm region in 2009. The result from that survey showed that elements such as arsenic were naturally elevated in some areas.

The threshold limit of sulfide-sulfur in the European Commission decision is 1000 mg/kg (1000 g/t, 1000 ppm or 0.1 %). Tunnel muck from the extractive industries should not exceed the threshold value of sulfide (see, https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32009D0359&from=EN). According to the Commission Decision one should follow the national threshold limits for elements listed. In Sweden we refer to national level values of less than low risk (MRR) for an assessment. An MRR-value for sulfide is not adopted why this is referred to the decision of the European Commission. MRR-values for other dangerous substances, As, Cd, Cr, Cu, Pb, Zn, Sb, Tl, Hg, Ni, Bi and Co, are adopted.

An important prerequisite to enable a proper estimation of any dangerous substances of a material is that you can relate analysis results to the local, natural background values. If measured elements of a material increase the local background values and are regarded as toxic for humans or the environment it may be categorized as contaminated and it should be taken care of.
Background levels are not possible to adopt in many areas of Sweden, like the Stockholm area, because of a shortage of necessary local lithogeochemistry data. For this reason no comparison between new analysis from construction sites and the local background levels is possible to do in these areas.

Current events

Albyberg 2016
One year after the construction project in Albyberg started heavy metals were leached from the crushed local bedrock. Due to sulfides from the rock the pH decreased in nearby water areas which finally lead to a leaching of heavy metals. The authorities stopped the work at the construction site and added carbonates in order to neutralize the acid-leaching from the aggregates. The bedrock was a sedimentary gneiss and at certain places you could see rust-colored rocks, but the bedrock was not heavily deep-weathered.

Gustavsberg 2018
At Gustavsberg, southeast of Stockholm, a major land area was uncovered. The bedrock from this area was excavated and crushed for a purpose to be re-used on site, for housing etc. Adjacent to the construction site acidic water was found. The water had increased levels of some metals and sulfur. The cost of depositing instead of using the excavated rock was estimated to several million euros.

Förbifart Stockholm 2019
One of the greater infrastructure projects in Sweden, The Stockholm bypass, has generated large quantities of tunnel muck. Some of these aggregates have not been able to dispose due to small sulfide elevations etc. The municipalities have been aware of this problem and need a better coordination from Swedish expert authorities to be able to make reasonable decisions and improve the material management situation. The value of all tunnel muck from the Stockholm bypass are estimated to 50 million euros.

Arlandapassagen 2020
Tunnel muck from a smaller underpass at road E4 north of Stockholm was sulfide increased. The aggregates not classified for continued use were transported to the nearest deposit, more than 30 kilometers away, for an additional cost of nearly 1 million euros. The bedrock was a sedimentary gneiss.

Haninge kommun 2020
In Haninge municipality a major housing project is ongoing. Excavation masses will be generated from this project, approximately 150 000 ton. According to preliminary investigations the rock is high in sulfide and categorized as a byproduct for further use. If the excavation masses are not used in the project, they must be transported to a deposit, and the additional cost will increase 10 million euros. The bedrock is a sedimentary gneiss.

Authorities and industry dialog
The question of dangerous substances is shared and managed by several authorities in Sweden. It is not a question with high priority and concerned parties often lack related knowledge of some issues, like geology. To optimize legislation, supervision, and procurement there is a common interest in providing guidelines for the facilitating of tunnel muck. The Swedish authorities want a simple but distinct approach in how to assess the geochemical status of water, soil and rock samples from infrastructure projects and what to do when the national or international limits are exceeded. Above all, common guidelines are needed, accepted by both the authorities and the industry, to enable a circular economy.

• How should the municipalities assess tunnel muck with a high sulfide content?
• Are there any geologic background data one can use in a specific area?
• Which type of workarounds should be used to minimize the environmental impact?
• What sort of requirements needs to be set for environmental control?
• How should a sampling be executed and how should the assessment of the result be carried out?
• Are there any functional and robust methods to buffer the sulfide rock that can be accepted from both the authorities and the industry?
• Is it possible to reduce the leaching issue directly at the source of the dangerous elements?
• Who oversees guidance and is responsible for producing guidelines about sulfide-carrying aggregates?
• Is the rock material less leachable in bond products, such as concrete and asphalt? Are these products therefore suitable for hosting sulfide carrying rocks?

Suggestions – Future ideas

Geochemical analysis, CE-marking
For new quarry licenses, the authorities sometimes request geochemical analyses of the bedrock. It´s reasonable to ensure that no rock materials from new quarries do not contain any dangerous substances, e.g. sulfide, by including lito-geochemistry analysis of the raw material for aggregates. The geochemical results can be included in the environmental impact statement with an assessment of the environmental impact. Finally, these analyses can be included in the CE-marking of the aggregates.

Investigation and assessment of the bedrock geochemistry in the Stockholm area
With a better geological model, based on lithogeochemistry data of the Stockholm-region, it will be possible to estimate the primary source of dangerous substances from the bedrock. The geochemical data of bedrock is one of the key issues to enable a circular economy of tunnel muck etc. With enough geochemical data we will be able to set a background image of a certain area and to facilitate eventual inappropriate rock materials – materials not suitable for excavation.

Dialog between authorities about the current regulations for dangerous substances
An impact assessment is needed to better understand what importance and which influence current regulations have and what effect they have on the construction activities of Sweden. The committee of circular economy for construction activities has suggested that the Swedish Environmental Protection Agency and the Geological Survey of Sweden will investigate and establish which construction materials should be classified as waste and as by-products.

Clear guidelines and supervision for extraction activities regarding dangerous substances
Guidelines in handling extraction masses are on the way from many different actors (Region Stockholm 2020, Exploateringskontoret Stockholm stad, on-going). It´s important that these guidelines don´t contradict each other, but instead use the same basis for assessment. To enable future extrusive masses to be managed it´s necessary that SGU and relevant actors from the industry and other authorities together establish a national guideline for extractive activities regarding dangerous substances. Guidelines will take time to create and relevant actors must meet early in this process to get an overview of the challenges that are linked to dangerous substances, possible improving changes that could be done and which consequences existing regulations and laws will result in.

Trade of aggregates may increase in the future
Aggregates tend to be perceived as international exportable products, like other types of goods. The construction market of Europe has changed from a local building market to a more international market. Today different aggregates with various properties are gathered from different regions of Europe – even from other countries. Aggregates have become global trade goods. Countries that lack certain aggregate types may import that from access areas. The countries around the Baltic sea are all strategic hubs to enable a circular economy of aggregates – long coastlines, sparsely populated and from a European perspective a good aggregate quality. For this reason it is important that there are similar guidelines and legislation of aggregates and tunnel muck in these countries. A good dialog between the Baltic sea countries enable a consensus of how we will classify both aggregates and by-products from the industry.

National on-going projects about sulfide-carrying aggregates
Sulfide-carrying bedrock in Sweden (Swedish transport administration 2020): The project aims to compile a lithogeochemistry database which represents the bedrock of all Sweden. The primary goal is the element of sulfur. Also, suitable detection methods and appropriate methods to handle sulfide enriched tunnel muck. A limit-value for increased sulfide content should also be proposed which may enable us to preliminarily risk classify the land.

Leaching of sulfide-rich rock masses (Swedish transport administration 2021): A sulfide rich rock turns into a severe problem only if the material oxidizes and leaches metals from the rock. The project aims to increase the knowledge of sulfide leaching processes of excavated rock masses.

Correlations studies (different projects): In constructions working hours are crucial to keep the cost down. Traditional lithogeochemistry testing may be time consuming but handheld XRF-instruments will provide a direct estimation of all elements of a material. The correlation between traditional lithogeochemistry and hXRF-analysis is crucial to minimize time loss, why some projects are investigating this.

A guideline – sampling and classification of sulfide carrying rocks (Exploateringskontoret i Stockholm 2020): A guideline of how sulfide carrying rock is going to be managed is being developed. What background information is needed to better perform a risk assessment is described. It is also proposed which type of geochemistry analysis should be performed.

*Region Stockholm 2020, Masshantering – Hantering av risk för sulfidhaltiga bergmassor i utbyggnad av tunnelbana i Stockholm: https://nyatunnelbanan.sll.se/sites/tunnelbanan/files/1410-P11-32-00007.pdf

Exploateringskontoret Stockholms stad, Nu pågående, Vägledning - provtagning och klassificering av sulfidförande berg

Trafikverket 2015, Trafikverkets handbok för sulfidförande bergarter https://trafikverket.ineko.se/Files/sv-SE/11741/RelatedFiles/2015_057_Trafikverkets_handbok_for_sulfidforande_bergarter.pdf*