DOI: 10.5593/SGEM2014/B11/S5.066


F. Chitea, D. Ioane, S. Adrian
Wednesday 1 October 2014 by Libadmin2014

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-07-0 / ISSN 1314-2704, June 19-25, 2014, Book 1, Vol. 1, 497-504 pp

In the vicinity of a refinery the shallow aquifer system is severely affected by historical oil pollution. Large quantities of petroleum products leaked into the ground during time, and despite the remediation actions, floating contaminants plumes are still affecting the area. By means of borehole data, a highly contaminated area was delineated, corresponding to a sector located inside the refinery and its vicinity. The first evidences of the aquifer pollution date since 1976, when the polluted area was analyzed, considering the floating- oil plume thickness. Even though the oil recovery processes executed in the area and the efforts made for diminishing the oil leakages, nowadays the geological formation and the groundwater are still affected by past contamination (residual fractions trapped into the soil) and recent leaks, as a consequence of handling accidents during storage and oil products transport. Since 2003, more accurate investigations were carried out in this area, consisting in volatile organic compounds and total hydrocarbon measurements. The samples were collected using over 150 boreholes (Phare RO 9910.02 project, coordinated by APMPH). The total sum of benzene, toluene, ethylbenzene and xylenes (BTEX) showed great variability both in time and space (2003 - 2006). According to the results of total hydrocarbons analyses, the contaminant plume developed in the south–eastern part of the refinery, the light non aqueous liquids affecting the phreatic aquifer and the soil. Due to the complex situation, in the frame of the research project GEOMON, a noninvasive investigation method was tested. Geoelectrical resistivity measurements were performed along profiles crossing the south-eastern sector of the contaminated plume. As the electrical resistivity data showed a good applicability in evidencing the contaminated areas, the geophysical investigation was extended. Eight field campaigns were completed from summer 2007 till spring 2014, to monitor the evolution of the contamination plume. Monitoring measurements showed important changes regarding electrical signature of the polluted aquifer. Apparent resistivity values for some of the VES stations were subject to a detailed time-lapse analysis. Considering the first apparent resistivity measurements (Summer 2007) as a reference base, percentage differences sections were constructed for the successive time intervals. Significant variation between data sets (> 25% of apparent resistivity normalized differences) observed along the VES profile were mainly ranging from the near surface (2m) to a depth of 8m, evidencing the effect of groundwater water table vertical displacements. As depicted from the geophysical data, from Summer 2007 till Summer 2008 the intensity of the oil pollution has decreased, but in Spring 2009 the intensity of the hydrocarbon pollution was again high. Till Spring 2014, the apparent resistivity data did not overcome the apparent resistivity results of 2007. Geophysical measurements, but also chemical analyses of water samples, showed that the aquifer is affected also by discharged industrial water, being unusable for drinkingor agricultural purposes.

Keywords: Vertical Electrical Sounding, oil pollution, apparent electrical resistivity, environmental pollution, phreatic aquifer contamination