A helicopter AEM survey providing an environmental assessment of the Eastfield quarry/landfill site, West Lothian, Scotland

This report describes an airborne electromagnetic survey carried out in February 2004 in the vicinity of the Eastfield quarry, former landfill situated in West Lothian, Scotland. The landfill is situated on the former Polkemmet colliery site. The survey consisted of 54 km of line coverage. The purpose of the survey was to investigate the capabilities of the technique in relation to mapping subsurface leakage and migration of conductive materials from a former waste disposal site. The survey took place some 24 years after closure of the 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 and 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 main site assessment covers a 600x600x100 m volume in the immediate vicinity of the landfill and Polkemmet Fault to the north. 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 is obtained for a variety of vertically compact, lateral migration pathways, largely below the base of the quarry. A limited amount of ground geophysical follow-up (Vertical Electric Sounding) has provided a degree of confirmation of the airborne conductivity model.