Lokaliseringens betydelse vid deponering av avfall på stort djup: Ett exempel med slutförvar för kvicksilverhaltigt avfall
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Many of the different substances used in our society today can be classified as harmful and dangerous. Mercury is one of the most dangerous toxins in our environment. In Sweden, decisions have been taken to stop all use of mercury and that the mercury existing in the Swedish society shall be collected and deposited in a safe way. The safest alternative for a final storage of mercury is considered to be a deep repository in the Fennoscandian bedrock. This also opens the possibility to use existing facilities such as a mine. The aim of this thesis is to illuminate what localization factors influence the functionality of a deep repository, mainly from a hydrogeological perspective. No direct demands has been set by the Swedish EPA that a deep repository must fulfil, instead the overall solution should be taken into account. Boliden Mineral AB’s plan for a deep repository for waste containing mercury and its two possible locations is used as an example. Boliden Mineral AB has large quantities of waste containing mercury at their smelting plant at Rönnskär. The company also has access to existing mines and they have the knowledge and the technology to build facilities deep in the bedrock. The main alternative is to build a repository deep in the bedrock under Rönnskär. The second alternative is to use the existing logistic facilities at the mine called Åkullagruvan, northeast of the community of Boliden, where plans exist to mine a new ore deposit. The best suitable alternative is the alternative with the least impact on the environment. The impact of the repository is dependent both on the size of the emission and the sensitivity of the environment where the emission surfaces. ercury is leached out of the waste by ground water seeping through the repository and then transported with the ground water until it reaches the surface. Where the contaminated ground water reaches the surface depends on the flow path of the ground water which in turn depends on the hydraulic conductivity and the hydraulic gradient. When the contaminated ground water reaches the surface depends on the length of the flow path and the speed of the ground water, which also depends on the hydraulic conductivity and the hydraulic gradient. To find out the magnitude of the negative impact on the environment of the contaminated ground water, the concentration of mercury in the ground water has to be known as well as the sensitivity of the environment where the ground water surfaces. The magnitude of the impact depends on the attenuation or dilution that occurs when the contaminated water surfaces. If the contaminated water surfaces in small waters and/or in a sensitive biotope the damages will be significantly larger than if it surfaces in a large river or a sea where the high dilution leads to a much smaller concentration of mercury. The hydraulic conductivity of the bedrock depends on the rock type, depth and the occurrence of fracture zones. Conducted tests show the hydraulic conductivity to be lower than the regional average for both example locations. The hydraulic gradient is high at the inland location of Åkulla and low at the coastal location of Rönnskär. These factors indicate the length of the flow path from the planned repository at Åkulla to be approximately 1 km and from Rönnskär approximately 400 m, and that the time for the ground water to surface will be between 1 000 – 10 000 years for the Åkulla location and 1 000 – 15 000 years for the Rönnskär location. After such a long time the land uplift occurring in the area will have changed certain parameters in the area as might a change in climate. Foremost the land lift will have an impact on the hydraulic gradient at Rönnskär and thus increase the ground water flow through the planned repository. The ground water flow through the example location of Åkulla was calculated to 1 500 – 7 500 litres per year and with a concentration of 0,012 mg of mercury per litre leachate water, a total emission of 20 – 90 mg of mercury per year can be expected. For the Rönnskär location, with a slightly higher ground water flow of 2 500 – 12 000 litres per year and the same concentration, a total emission of 30 – 140 mg per year can be expected. After the effect of 3 000 years of land lift is taken into account, the total emission from a repository at the Rönnskär location can be expected to be 70 – 350 mg of mercury per year. When a contaminated ground water from the Åkulla location surfaces in the lake Stavträsket it will be diluted around 400 000 – 2 100 000 times and will give the lake an additional mercury concentration of 5,6•10-6 – 2,8•10-5 µg/l. A contaminated ground water flow from the Rönnskär location surfaces at the mouth of the Skellefteå River, which has a much higher discharge than Stavträsket. The dilution there reaches 2•108 – 9•108 times and gives the Bothnian Bay an additional mercury concentration of 1,4•10-8 – 7,0•10-8 µg/l. Compared to the background concentrations of Stavträsket, < 5•10-3 µg/l, and Bothnian Bay, 1,3•10-2 µg/l, these additional concentrations are negligible. The impact of a deep repository on the local ground water is unquestionable regardless of the location. With an inland location the surfacing, contaminated ground water will always have a relatively restricted discharge area and thus a restricted possibility of dilution and a higher risk of too high concentrations of the potentially dangerous substances in local waters. With a coastal location the discharge will occur closer to larger bodies of water that are more resilient than the smaller waters of an inland location.
Place, publisher, year, edition, pages
2011. , 47 p.
Life Earth Science
Bio- och geovetenskaper, kvicksilver, djupförvar, lokalisering, gruva, berggrundens egenskaper, hydrogeologi, grundvatten, vattenbalans, flödesväg, genombrottstid, förorening
IdentifiersURN: urn:nbn:se:ltu:diva-53952Local ID: aeeaeb29-fcca-4e1c-a60f-801474672ba8OAI: oai:DiVA.org:ltu-53952DiVA: diva2:1027331
Subject / course
Student thesis, at least 30 credits
Validerat; 20110730 (anonymous)2016-10-042016-10-04Bibliographically approved