With rising population, the earth’s available water resource has been experiencing stresses and inevitable water scarcity might be looming (Ahner, 2013; Anuforom, 2013). Groundwater is a water resource that can cope with rainfall variability, alleviate growing water scarcity, contribute to food security and regional growth as well as mitigate the risks resulting from the effects of climate change on the hydrological cycle (IGRAC, 2018). Prior to 1970, there was low infrastructural development in sub-Saharan Africa and populations clustered around the wetlands because the outskirts and hinterlands had no water for survival; the only source of groundwater was from natural springs and artesian wells (Foster et al, 2006; Adelana and MacDonald, 2008). Also, from shallow hand-dug wells within the regolith that gave water supplies and abandoned after failing to yield (Jones and Hockey, 1964; Ajayi and Abegurin, 1994). With the advent of technology, however, advanced drilling tools became accessible and affordable. As a result, people began to migrate from the core clusters to the outskirts and hinterlands, but issues with wildcat and abortive boreholes continued unabatedly (Foster et al, 2006; Adelana and MacDonald, 2008).
In the past, borehole designs and completion have been taken for granted with the aftermath that many have either failed to yield optimally or dried up. Several boreholes have been appraised in different geological settings to identify the causes of their failures (Ajayi and Abegurin, 1994; Adiat et al., 2013). Borehole failure arises when a borehole that has been successfully drilled, subsequently failed to deliver sufficient yield of safe water throughout the year. According to Ajayi and Abegurin, 1994 amongst the causes of borehole failures are: tapping from aquiclude (i.e., a geological formation which is impermeable to the flow of water but porous e.g., shale), seasonal fluctuations in water level, improper casing of the overburden and pump failure.
During the last four decades, when deep exploration techniques were deployed for near-surface investigations, wildcats and abortive boreholes had became a thing of the past (Hubbard and Linde, 2011; Deng et al., 2016). Although the introduction of hydro-geophysics reduced wildcats and abortive boreholes to a certain extent (Hubbard and Linde, 2011; Binley et al, 2015 and Deng et al, 2016), more advanced point-scale geophysical techniques have since been introduced such as electrical methods (e.g., 1D depth sounding, electromagnetic (e.g., Time Domain Electromagnetic and Frequency Domain Electromagnetic). Considering the need for improved water supplies, there is an urgent need to develop mechanism and strategies to enhance quality of water and borehole construction.
The University of Ilorin (UNILORIN), North-central Nigeria has an existing tripartite water regime consisting of municipal water from Asa and Agba dams, a mini university dam completed to augment the municipal water with river Oyun being the main source (Abdulkadir, 2016; Salami et al, 2016), and a few dispersed water boreholes on the university landmass. Despite this seemingly composite water regime aimed at eradicating water insecurity, there are still cases of water scarcity within and around the University. The municipal water is not reliable, and the dam is vulnerable to seasonal variability. Olasunkanmi et al. (2012) suggested the possibility of fractured basements at certain points along the dam bank from a depth of about 10 m downward acting as zones of anomalous seepage which can be inimical to the continuous water retention of the dam. In a related study, Olukanni et al. (2017) showed that the University’s dam has about twenty of its thirty baffle blocks damaged causing the dam to experience some structural relapse from seepages through its foundation.
There are concerns that the groundwater which should be the most reliable component of the existing water regime is also not very productive and dependable despite claims that geophysical surveys were carried out before the boreholes were drilled. Although Salami et al. (2013) indicated that there was no serious water problem in the region because the availability seemed higher than the present use. This is inconsistent with reality and the results of numerous studies which show that some parts of the region are highly water-stressed (Adelana, 1988; Nwankwo, 2002; Olasehinde and Raji, 2007; Olasehinde 2010; Nwankwo, 2011; Lawal et al, 2012; Olawepo et al, 2013; Lawal et al, 2016; Olatunji et al, 2017; Olatunji et al, 2020 and Fawale et al, 2020). Thus, in this present work, the rationale behind drilling of boreholes within the University of Ilorin landmass was investigated. In the light of this, two possible rationales were defined: (i) scientifically-guided/geoscientific motive (i.e., due to scientific necessity and after appropriate geophysical evaluation), and (ii) resources-based/logistics motive (i.e., constrained by cost, proximity, or just mere cosmetic projects). The main contribution of this study is the application of geospatial analysis for retrospective validation and post-development (i.e., post-drilling) evaluation of boreholes.