Regional Aquifer Vulnerability and Pollution Sensitivity Analysis of Drastic Application to Dahomey Basin of Nigeria

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 affecting 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.

Development of a groundwater contamination index based on the agricultural hazard and aquifer vulnerability: Application to Portugal

“…The relative weights for each parameter were computed emulating the approach to calculate "effective weights" in single parameter sensitivity analysis. This approach is widely used to assess the influence of the vulnerability parameters of the DRASTIC method (Krogulec and Trzeciak, 2017;Oke, 2020;Rajput et al, 2019;Tomer et al, 2019). Firstly, vulnerability was calculated by setting w rt to 0.6, and w slope and w soil texture to 0.2, as the theoretical weights.…”

Pore Structure and Seal Capacity of Ilaro Formation Shales in the Eastern Dahomey Basin: Implications from Mercury Injection Capillary Pressure and Spontaneous Imbibition Analyses

“…A recently proposed stratigraphic scheme for the offshore eastern Dahomey basin (Figure ) shows the integration of units correlated from adjacent Nigerian basins (e.g., the offshore section of the Araromi formation was correlated to the Nkporo shale of the Anambra basin). However, the current stratigraphic consensus has the onshore section of the same basin as comprising the Cretaceous Abeokuta group, which comprises of the Ise, Afowo, and Araromi formations and the Cenozoic Ewekoro, Akinbo, Oshosun, Ilaro, and Benin formations. , …”

“…However, the current stratigraphic consensus has the onshore section of the same basin as comprising the Cretaceous Abeokuta group, which comprises of the Ise, Afowo, and Araromi formations and the Cenozoic Ewekoro, Akinbo, Oshosun, Ilaro, and Benin formations. 25,26 Stratigraphically Figure 2, sedimentation within the onshore eastern Dahomey basin commences with the early Cretaceous Ise formation consisting of continental sands, grits, silts, sandstones, and conglomerates overlying the basement followed by the Afowo formation comprising sandstone and shale and the Araromi formation consisting of fine−mediumgrained sandstones, organic-rich shales, and siltstones with thin limestone intercalations (Figure 2). 21,27 The Araromi formation is overlain by the Ewekoro limestones followed by the Akinbo shales.…”

An Evaluation of Groundwater Vulnerability Assessment Methods in a Rapidly Urbanizing City: Evidence From Dakar, Senegal

“…Among the different overlay and index methods, DRASTIC is one of the most popular due to its performance and ease of use (Barbulescu, 2020). In the last two decades, DRASTIC has been employed in several studies to assess groundwater vulnerability in Asia (Babiker et al, 2005;Yin et al, 2011;Ghosh et al, 2015), Africa (Jourda et al, 2007;Saidi et al, 2009;Hamza et al, 2008Hamza et al, , 2010Neh et al, 2014;Oke, 2020), and the Americas (Klug, 2009;Ferral et al, 2014;Agyemang and Beauty, 2017). DRASTIC does not, however, explicitly consider spatial variability in anthropogenic factors that may be of critical importance in rapidly urbanizing, lowincome areas (Singh et al, 2015).…”