Environmental geology of a planned building site in Kungälv, SW Sweden: site characterization and remediation of potential concerns

Abstract

Åseberget is a low-lying hill and planned building site in Kungälv, southwestern Sweden. The potential contaminants and complications of construction work are of a great concern as the area has previously been utilized as a landfill. A planned building site requires careful examination of potential obstacles and uncertainties before any construction work is initiated. Earlier field measurements have shown that the area is contaminated with gas; there are significant levels of methane gas that could pose a risk of explosivity if they reach 5-15% in air. The filling material of the site is generally unknown. However, through several field investigations, it appears to consist mostly of masses of soil such as clay. The purpose of this report is to characterize Åseberget, investigate the field data of gas levels, discuss building technical solutions, and try to evaluate the suitability of the area for construction. The method used in this report was mainly through the study of literature by reading field reports from earlier investigations of Åseberget. As well as other relevant literature sources to find adequate data and information about building technical solutions, methane gas, landfills, and so on. Another approach was to assemble the field data and create maps showing the measured variation of gas levels across the area. The result shows that the methane gas levels are fluctuating and that it can range from 0% up to 100% in different locations across the landfill. The source of the gas is thought to derive from inclusions of organic material such as humus, peat, grass, and moss. The gas is assessed to be located in pockets in the ground and eventually will completely mitigate over time, but development of the area will most likely cause new pathways of gas migration and potential accumulation inside temporary construction sites and future permanent residential buildings. The site will be buildable if the potential risks of accumulation of methane gas are considered and included in the plans of development. The most recommended and utilized building technical solution for gas-contaminated land is sub-slab depressurization as well as installing impermeable plastic membranes into the concrete or timber foundation. Nevertheless, the biggest risk lies in the construction work itself, which creates new gas migration pathways, potential spaces for accumulation and ignition sources. This therefore requires careful planning and consideration of the working conditions to prevent any hazards.