High levels of nickel from sulphide soil in Umeå's raw water : Modeling of groundwater flow and mass transport in Forslunda aquifer

Abstract: The raw water in some of Umeå's abstraction wells has shown high nickel levels for more than a decade. The cause has not been determined but there is an investigation from 2010 where the results indicate sulphide clay found adjacent to two basins used for artificial infiltration. The previous investigation further declares that the leaching occurs due to oxidation in an unsaturated state when the groundwater is lowered. However, the data points used for the investigation are limited and the source references are few. Today, over 10 years of data have been collected and the number of published scientific articles dealing with sulphide soils has increased, which motivates a follow-up on the subject. This degree project aims to contribute with further knowledge to the issue of high nickel concentrations in raw water with the purpose to strengthen or reject the hypothesis by: performing a literature review on sulphide soil; comparing nickel level with groundwater level; constructing a groundwater model and performing simulations. A large database is available from various investigations performed on the site from the 1940s until today. The literature review shows that the geological conditions exist for sulphide material to be present in the area, as well as several studies and investigations that confirm the suspicion of the presence of sulphide soil. Furthermore, the data points show a correlation between the groundwater level and the nickel concentration in raw water from extraction wells 17 and 20. The most obvious interpretation is the decrease in the nickel content as the groundwater level is raised, although a low groundwater level indicates high nickel levels. The modeling of the groundwater flow and mass transport shows how nickel can move from the area of suspected sulphide material to the extraction wells. An overall assessment of the project strengthens the thesis, however, more investigations are needed to exclude uncertainties inherent in the result.