Detection of potential pathways for contaminants into the Päijänne Tunnel in Finland

Abstract

The potable water for a million people residing in the Helsinki metropolitan area is conveyed from Lake P\u00E4ij\u00E4nne along the 120 km-long P\u00E4j\u00E4nne Tunnel. Information on the hydrogeology of the tunnel is vital for land-use planning, particularly in the southern part of the tunnel line where industrial activity and pressures to build underground constructions are increasing. In a project commissioned by the Helsinki Metropolitan Area Water Company, the areas vulnerable to contamination and possibly hydraulically connected to the tunnel have been identified and spatially analysed in relation to risk activities and infrastructure. The project complements an earlier study in which potential risk activities were located and characterised. Relevant information on the soil, groundwater and bedrockfracturing conditions along the length of the tunnel was extracted from tunnel construction documentation and areal environmental datasets, and assembled as overlays in GIS format. As a result, a description of the environmental geology of the tunnel zone has been produced, and the estimated area of influence has been delineated as a support to land-use planning.