Assessment of Borehole Failure in the Global South: Integrated Hydrogeological and Geophysical Evidence from Gombe Metropolis, Northeastern Nigeria

Abstract

Groundwater underpins domestic water supply across much of the Global South, yet chronic borehole failure continues to undermine investment in water-supply infrastructure, particularly in geologically heterogeneous sedimentary basins where site selection is rarely constrained by integrated subsurface data. This study presents an integrated hydrogeological, geophysical, and statistical assessment of groundwater occurrence and borehole performance in Gombe Metropolis, northeastern Nigeria, a rapidly urbanizing city of approximately 450,000 people situated within the Gongola Sub-basin of the Upper Benue Trough. A compiled inventory of 71 borehole records (depth, functional status, and, where available, yield) was cross-referenced against 23 Vertical Electrical Sounding (VES) stations acquired using the Schlumberger configuration, in order to constrain otherwise non-unique geoelectric interpretation with authentic subsurface ground-truth. Complete depth and functional-status data were available for 58 of the 71 boreholes (35 functioning, 23 not functioning), forming the basis for formal statistical testing, while a richly documented subset of 32 boreholes (24 with individually reported depths) supported a ward-level qualitative analysis of failure mechanisms. Non-functional boreholes cluster in the wards of Bolari and Jakada Fari at shallow-to-intermediate depths, where thick sequences of the Pindiga (Fika) Shale, ironstone intercalations within the middle member of the Gombe Formation, and structurally attenuated stratigraphy act as hydrogeological barriers; however, a Mann–Whitney U test across the full 58-record subset found that borehole depth alone did not significantly distinguish functioning (mean 86.6 ± 29.3 m) from non-functioning boreholes (mean 72.0 ± 31.0 m; U = 505.0, p = 0.105, rank-biserial r = 0.255). Across the 23 VES stations, groundwater potential was descriptively associated with aquifer lithology (Cramér's V = 0.423) though this did not reach significance in a Fisher–Freeman–Halton exact test (p = 0.458) given the small, sparse sample; clean, fine-grained sand and sandstone units nonetheless hosted the majority of highpotential occurrences, whereas silty and clay-dominated facies were predominantly moderate to poor except where deeply confined (> 135 m). In contrast, aquiferous depth was strongly and significantly correlated with VES-derived groundwater-potential class (Spearman ρ = 0.682, p < 0.001; Kruskal–Wallis H (2) = 12.63, p = 0.002). A shallow functional outlier and a faultassociated deep success zone near Pantami confirm that depth alone is an incomplete predictor of borehole outcome. Taken together, the statistical and geological evidence indicates that borehole failure in Gombe Metropolis is governed jointly by aquiferous depth and lithological confinement rather than by depth in isolation, and that borehole ground-truthing is indispensable for resolving the inherent ambiguity of VES interpretation in structurally complex sedimentary terrains. The findings provide an evidence-based basis for depth-targeted drilling, ward-specific development planning, and groundwater protection policy in Gombe and analogous basins across the Global South.