An AEM survey of a leaking landfill

This study presents results obtained from a remarkably small-scale helicopter airborne electromagnetic (AEM) survey of a closed landfill. The landfill, occupying a former quarry, is situated among shallow, worked-out coal seams (pillar and stall workings) and was located over at least two mineshafts that occupied the quarry floor. The landfill was known to be leaking from an extensive borehole investigation that took place in the 1970’s, when the landfill was active. Redevelopment issues and associated, proposed surface extraction of coals have renewed interest in the possible pollution threat of waste products. Of particular concern is the extent to which pollution has, potentially, transgressed a fault to the north and entered the area of proposed regeneration. The airborne survey data (EM and magnetic) were obtained using the six-frequency RESOLVE bird using a flight line spacing of 40 m. The data acquired have been subjected to 1D regularized inversion to enable a 3D conductivity model to be assessed. The model clearly identifies the landfill as a source term of highly conductive materials. At conductivities that are a factor of 3 above background, evidence for a variety of vertically compact, lateral migration pathways, largely below the base of the quarry, is obtained.