Integrated Hydrogeochemical and Microbial Risk Assessment of Sandstone Aquifers in Tropical Sedimentary Basins: Methods, Controls, and Public Health Implications

Esomchukwu Jennifer Onyeka (Nnamdi Azikiwe University, P.M.B. 5025 Awka, Anambra State - Nigeria)
Charles Onyeka Nwamekwe (Nnamdi Azikiwe University, P.M.B. 5025 Awka, Anambra State - Nigeria.)
Ifeanyichukwu Benjamin Unigwe (University of the West of England, Frenchay Campus, Coldharbour Lane, Bristol, BS16 1QY, United Kingdom.)

Nexus: Journal of Cross-Disciplinary Insights
Vol. 2 No. 1 (2026): Interdisciplinary Innovation for Sustainable Development

Sandstone aquifers in tropical sedimentary basins are major groundwater reservoirs, yet their public-health safety is often underestimated when assessment is restricted to physicochemical quality. This review addresses the persistent mismatch between chemically acceptable groundwater and microbiologically unsafe water, especially in shallow, permeable aquifers exposed to intense rainfall, pit latrines, septic systems, dumpsites, agricultural runoff, and weak wellhead protection. A structured narrative synthesis was conducted using peer-reviewed hydrogeological, hydrogeochemical, microbiological, vulnerability, and environmental health studies from Scopus, Web of Science, ScienceDirect, SpringerLink, and Google Scholar. The review focused on tropical sandstone aquifer systems in Africa, Asia, and South America. It examined lithological controls, major-ion evolution, microbial indicators, contamination pathways, WHO-based classification, Water Quality Index applications, contamination indices, multivariate statistics, GIS-based vulnerability mapping, and integrated hydro-microbial risk scoring. The synthesis shows that groundwater chemistry is governed mainly by silicate weathering, carbonate dissolution, cation exchange, shale interbeds, residence time, and anthropogenic inputs. However, chemical compliance does not confirm potable safety. Reported evidence includes TDS below 500 mg/L in chemically acceptable Nigerian basin aquifers, while all 12 shallow wells in Abeokuta tested positive for total coliform and Escherichia coli. Microbial loads increased during wet seasons, with Calabar groundwater recording total coliform increases from 76 to 468 CFU/100 mL and Salmonella/Shigella reaching 1081 CFU/100 mL. DRASTIC mapping further classified 21% of the Dahomey Basin as highly vulnerable. The review therefore proposes an integrated framework linking hydrochemistry, microbial evidence, vulnerability, GIS, and health-risk interpretation for safer, adaptive, and evidence-based groundwater governance.