Environmental Geophysics Investigation of an Abandoned Petroleum Tank Farm in Warri, South South Nigeria

Abandoned petroleum tank farms represent significant environmental liabilities across the Niger Delta, and the former tank farm at Warri in Delta State has been identified as a priority remediation site following community complaints of persistent hydrocarbon odours and discolouration of nearby water sources. This study employs electrical resistivity tomography and total petroleum hydrocarbon soil analysis to characterise the extent of subsurface contamination at and around the abandoned facility. Eight ERT profiles totalling 2,400 metres of survey line were acquired using the Wenner-Schlumberger array across the tank farm footprint and a buffer zone extending 150 metres beyond the facility perimeter. Anomalously low resistivity zones of 1 to 15 ohm-metres are identified beneath former tank bases and along what are interpreted as former pipeline corridors. Elevated resistivity zones at depths below 12 metres at two locations are consistent with LNAPL pooling above the capillary fringe of the water table. Soil samples collected at geophysically guided locations confirmed total petroleum hydrocarbon concentrations between 2,500 and 48,000 milligrams per kilogram at affected points. The study delineates the contamination plume geometry and estimates a minimum affected volume of 18,000 cubic metres of soil requiring remediation. Findings inform a phased remediation plan prepared in accordance with the NOSDRA standards. Keywords: tank farm contamination, electrical resistivity, TPH, Warri, Delta State