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Groundwater Aquifer Vulnerability Assessment using a Dar-Zarrouk Parameter in a Proposed Aboru Residential Estate, Lagos State, Nigeria
AYUK, MA
Abstract
The need to build an automobile mechanic settlement, abattoir and a proposed meat processing factory at
Aboru residential estate necessitated a geophysical assessment (using a Dar-Zarrouk parameter – longitudinal unit
conductance, S) of the vulnerability of the subsurface aquifers in the study area against the expected long-term
anthropogenic impacts of these facilities on the groundwater system. Thirteen (13) Vertical Electrical Sounding (VES) points
and four (4) Dipole-Dipole resistivity profile lines were occupied on four traverse lines across the study area. Isoresistivity
and Isopach maps were generated and Total Longitudinal Unit Conductance, S of the earth materials overlying the aquifer
was computed and the aquifer protective capacity (APC) map was generated. The VES delineated four (4) geo-electric layers
namely; topsoil, pebbly/lateritic sand, clay/clayey/silty sand and sandstone. The depth to the sandstone aquifer ranges from
30.6 – 39.4 m with resistivity values ranging from 851 – 1437 Ωm. The iso-resistivity and isopach maps reveal that the near
surface lateritic materials with resistivity values ranging from 350 – 1150 Ωm and thicknesses ranging from 2 – 29 m are
pervious. The Total Longitudinal Unit Conductance, S varies from 0.0164 - 0.1168 mhos indicating a poor to weak protective
capacity rating across the study area and the APC map reveals that the north-eastern and western parts of the study area show
areas with weak protective capacity ratings while other areas are characterized by poor protective capacity rating. As such,
the establishment of the proposed service facilities in the study area is strongly discouraged as the nature of their operations
has a high potential to contaminate and eventually pollute the sub-surface aquifers on the long-run. If however the
inevitability of their establishment cannot be set-aside, then secondary measures must be taken to forestall a direct impact of
their operations on the subsurface.
Keywords
Aquifer; Dar-Zarrouk; Vulnerability; Longitudinal Unit Conductance
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