Mapping the extent of a Norwegian ravine-filled closed landfill site using a combination of electrical methods

Landfills contribute to serious problems in our society, including toxic leachates contaminating groundwater and soil, methane and CO₂ emissions, and infrastructure damage caused by the degradation of organic material. 

Brånåsen landfill, located in the municipality of Lillestrøm, Norway, is situated in an old ravine within marine deposits. The area is currently utilized for residential, agricultural, and recreational purposes. The landfill has caused numerous challenges since its closure in 1991, including methane gas emissions and damage to residential properties, resulting in stress on residents, lawsuits, and significant compensation costs. 

In recent years, extensive research has been conducted on Brånåsen landfill to delineate its outer borders with Electrical resistivity tomografy (ERT) and assess methane gas emissions. 

Electromagnetic (EM) surveys offer fast mapping of ground conductivity, making it possible to cover a larger area over a short period of time compared to ERT surveys. Where ERT is relying on good connection with the grounds surface, EMmeasurements can be executed independent of surface material, making it a potential substitute and/or addition to ERT measurements. This study focuses on mapping the outer borders of the landfill using the Geonics EM34-3 and EM38-MK2 instruments. Brånåsdalen landfill provides an ideal site for testing this method due to previous research and the area’s diverse usage. Agricultural land offers an environment with minimal cultural noise, while residential and park areas test the limits of the equipment’s effectiveness in noisier conditions. The data collected from the electromagnetic (EM) survey is compared with previous research utilizing Electrical Resistivity Tomography (ERT) and maps of the assumed borders developed by Norconsult.  

The EM34-3 was deployed in both horizontal and vertical dipole configurations, with transmitter-receiver antenna spacings of 10 m, 20 m, and 40 m, to measure conductivity at varying depths and test the equipment’s sensitivity to noise under different settings. EM38-mk2 was used in vertical dipole with an effective skin depth of 1,5m. 

The results show an increase in electrical conductivity values that mostly align with the previously assumed map of the landfill. However, significantly higher values were observed in residential areas compared to agricultural land. The data suggests that the equipment is less sensitive in horizontal dipole mode and with shorter antenna spacings, making it more suitable in areas with human interference. Overall, the equipment is effective for fast mapping areas with minimal human interference, like farmland. Combining EM data with ERT for control measurements in areas of interest is recommended for improved accuracy.