Abstract:
Shallow groundwater vulnerability mapping of the southwestern Nigeria sedimentary
basin was assessed in this study with the aim of developing a regional-based vulnerability map
for the area based on assessing the intrinsic ability of the aquifer overlying beds to filter and
degrade migrating pollutant. The mapping includes using the established seven parameter-based
DRASTIC vulnerability methodology. Furthermore, the developed vulnerability map was subjected
to sensitivity analysis as a validation approach. This approach includes single-parameter sensitivity,
map removal sensitivity, and DRASTIC parameter correlation analysis. Of the Dahomey Basin, 21%
was classified as high-vulnerability and at risk of pollution, 61% as moderate vulnerability, and 18%
as low vulnerability. Low vulnerability areas of the basin are characterised by thick vadose zones, low
precipitation, compacted soils, high slopes, and high depth to groundwater. High-vulnerability areas
which are prone to pollution are regions closer to the coast with flat slopes and frequent precipitation.
Sensitivity of the vulnerability map show the greatest impact with the removal of topography, soil
media, and depth to groundwater and least impact with the removal of the vadose zone. Due to the
subjectivity of the DRASTIC method, the most important single parameter a ecting the rating system
of the Dahomey Basin DRASTIC map is the impact of the vadose zone, followed by the net recharge
and hydraulic conductivity. The DRASTIC vulnerability map can be useful in planning and siting
activities that generate pollutants (e.g., landfill, soak away, automobile workshops, and petrochemical
industries) which pollute the environment, groundwater, and eventually impact the environmental
health of the Dahomey Basin’s inhabitants.
