Abstract
This research is concerned with characterization and assessment of Natural Attenuation of hydrocarbon contaminated site. The specific study site is Baruwa community in Alimosho Local government area of Lagos state, Nigeria, with a population of over 100,000 people. There are over 150 wells within the community which have been affected by the oil pollution which dates back to 1994, when there was a burst in an N.N.P.C (Nigerian National Petroleum Corporation) Valve pit located at the Federal Housing Estate (Jakande Estate) opposite the study site. Earlier studies carried out by Adekunte (2008) and Balogun (2009) have established a case of the pollution of the groundwater via hydro-chemical analysis and geoenvironmental assessment coupled with stratigraphic characterisation of the contaminated site using wells within the area respectively. This study employed the collection of field data in 2014 from the contaminated site to sufficiently characterize the hydrocarbon contamination within the area. Characterization of the study area was conducted utilizing the methodology prescribed by United States Environmental Protection Agency (USEPA, 2001). 25 Hand dug wells to a depth of 26.5 metres within the area were utilized for the study. Water levels and Free Hydrocarbon Thicknesses were measured with the aid of an oil/water interface meter, Total Petroleum Hydrocarbon (TPH) was also measured both in groundwater and soil vapour using a portable Hydrocarbon Analyser. Comparisons were made with data obtained in 2006 of previous studies and Natural Attenuation occurrence established based on Tiers 1 and 2 criteria (USEPA, 1999). LNAPL thickness decreases of 86.4% to 99.7% were recorded in comparison with that from previous studies (2006 - 2014). TPH surveys carried out in the groundwater are in agreement with LNAPL flow direction. Decreases in TPH concentrations varying from 33.13% to 57.61% were observed in comparison with earlier studies (2006 - 2014). All the wells investigated within the study area indicated that significant Natural Attenuation has occurred over the period (2006 - 2014).