TITLE:
Integrated Geoelectrical Resistivity Method for Environmental Assessment of Landfill Leachate Pollution and Aquifer Vulnerability Studies
AUTHORS:
Stanley U. Eze, Omafume M. Orji, Abriku E. Onoriode, Saleh A. Saleh, Macpaul O. Abolarin
KEYWORDS:
Leachate Contamination, Groundwater Pollution, 2D and 3D Electrical Resistivity Tomography (ERT), Aquifer Vulnerability, Environmental Assessment
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.10 No.9,
September
6,
2022
ABSTRACT: Leachate plumes from landfills are a major source of pollution in
Nigeria, especially in urban areas.
Assessing leachate contamination in the subsoil is considered a complex
process that needs detailed field measurement to accurately define the extent
of contamination. To ascertain the extent of pollution of the subsoil and groundwater sources which were
reportedly contaminated by leachate plumes from an old dumpsite located
in Osubi town, an integrated geo-electrical method involving 1-D vertical
electrical sounding (VES) and 2-D, 3-D ERT techniques were employed. Orthogonal
set of 2-D apparent resistivity data was collected in a 100 × 50 m2 rectangular grid around the
dumpsite, using the Wenner array. Two years
later, three (3) 2-D resistivity imaging profiles were also recorded in
time-lapse mode at the dumpsite to monitor the possible effects of attenuation
on the leachate over time. Ten (10) VES data were also acquired and used along
with the 2-D imaging data. 2-D apparent resistivity data were inverted with Dipprowin software program. The orthogonal set of 2-D
lines of apparent resistivity was merged
into 3-D data and inverted with RES3DINV program to create a 3-D subsurface
resistivity model. Geological models observed from 2-D and 3-D resistivity
inversion revealed low resistivity values in the order ρ Ω·m which is
indicative of leachate plumes in the saturation zone (pore water). The 2-D
resistivity-depth sections imaged low resistivity leachate plumes at the near
surface (ant within the first, second
and third layers at depth ranging from 0.00 - 2.50 m,
2.50 - 5.38 m and 5.38 - 8.68 m respectively. Thus, leachate contamination clearly increased with depth beyond the depth of first and second
aquifers in the area which implies that available groundwater for domestic use
is already contaminated with leachate from the dumpsite. Leachate
contaminant-depth map estimated for the second geoelectric layers for VES 2, 3,
4, 7, 8, 9, and 10 shows that the second layer has been invaded completely by
leachate contamination up to 6.5 m depth. 2-D apparent resistivity data
acquired two years after show lower resistivity anomalies of the leachate plume
caused by time-lapse attenuation effect on the observed resistivity of the leachate. This indicates that the leachate plume has
become more conductive and toxic to the environment. The Longitudinal
conductance map of the area shows that the aquifer protective capacity of this
area is weak (0.1 - 0.19 Mho) thus, aquifers in the area are prone to pollution from the
dumpsite. The three techniques used in this study (2-D, 3-D ERT and 1-D VES)
fitly provided crucial information on the
degree of contamination caused by the landfill leachate plume.
Therefore, it is advisable to implement an environmental remediation and
leachate management program.