The earth construction actions like excavation and lowering of drainage level has been recognized as a potential environmental problem in coastal areas of Finland due to of acid sulphide soils (ASS). The foregoing actions cause oxidation of sulphide minerals to sulphide and formation of sulphuric acid. The acid drainage water from the excavated ASS can dissolve harmful heavy metals e.g. aluminium, manganese, cadmium etc. from the soil to the aqua system (Sutela et. al 2012). In Southern Finland, ASS occurs mainly in fine grained muddy clay sediment in the coastal areas of Finland. The sulphide mineral containing ASS sediments were formed during Litorina sea phase 7500-4000 years ago due to anaerobic reduction of sulphur in the bottom of the ocean (Finnish ministry of agriculture and forestry, 2011). In northern Europe, the ASS is found to be problem also in the coastal areas in Sweden.
The ASS is problematic in Southern Finland where lot of construction activities and excavation is carried out. Geological survey of Finland (GTK) have been mapping the of ASS areas previously in Ostrobothnia and at the moment in the metropolitan area of Finland. The methods and instructions for identifying and testing of ASS exist in the literature. However, the lack of application directive for existing methods and the instructions for handling of excavated ASS in infra construction projects has been identified as a major problem. Therefore, the major cities in Southern Finland (Helsinki, Espoo, Vantaa) together with Ramboll, Geological survey of Finland (GTK), local Centre for Economic Development, Transport and the Environment (Uusimaa) and Helsinki Region Environmental Services Authority (HSY) have been started to prepare the instructions for ASS. The project is divided in three phases: 1) collecting the existing knowledge and best practices from the previous Finnish studies and foreign ASS guidelines for preliminary report, 2) the experimental part which is focused on comparing previously used field- and laboratory test methods and to find the most applicable ones for ASS identification and risk evaluation and 3) to produce instructions for the use of contractors and clients in Southern Finnish region on testing, evaluating and handling of ASS based on the preliminary report and experimental results. The instructions are to be published in spring 2018.
Works sited:
Finnish ministry of agriculture and forestry, Ympäristöministeriö, 2011. Happamien sulfaattimaiden aiheuttamien haittojen vähentämisen suuntaviivat vuoteen 2020. Finnish ministry of agriculture and forestry reports 2/2011. Pp 26.
Sutela, T. et. al., 2012. Happamien sulfaattimaiden aiheuttamat vesistövaikutukset ja kalakuolemat Suomessa,Finnish environmental Institute reports14/2012, Helsinki: Edita Prima Oy.
