Background, Indiscriminate household waste disposal poses a critical and growing threat to shallow groundwater resources in rapidly urbanising secondary cities across north central Nigeria. Okene, the administrative headquarters of Okene Local Government Area in Kogi State, exemplifies this challenge, three decades of population growth without commensurate investment in solid waste management infrastructure have produced widespread unregulated open dumpsites overlying a vulnerable Precambrian basement complex aquifer system upon which the majority of households depend for daily domestic water supply.

Methods, A cross-sectional investigation was conducted across 36 groundwater sampling points (hand-dug wells and boreholes) stratified across three contamination intensity zones defined by proximity to identified waste disposal sites. Comprehensive physicochemical analysis (16 parameters), heavy metal quantification (Pb, Cd, Fe, Zn) by atomic absorption spectrophotometry, and microbiological enumeration (total coliforms and Escherichia coli) were conducted during both dry (February 2025) and wet (July 2025) sampling campaigns. Geographic Information System-based Inverse Distance Weighting (IDW) interpolation was applied for spatial contamination gradient mapping. Quantitative health risk assessment followed the USEPA (2011) exposure framework for non-carcinogenic (Hazard Quotient and Hazard Index) and carcinogenic (Incremental Lifetime Cancer Risk) end points for adult and child receptors.

Results, Zone A (within 100 m of dumpsites) groundwater exhibited mean pH of 5.31 (dry) and 5.89 (wet), below the NIS 554,2015 permissible range of 6.5 to 8.5. Lead (0.041 mg/L dry) and cadmium (0.017 mg/L dry) concentrations exceeded NIS 554,2015 limits of 0.01 mg/L and 0.003 mg/L respectively. Total coliforms (1,820 CFU/100 mL) and E. coli (680 CFU/100 mL) were detected in all Zone A samples. Hazard Index values for Zone A were 2.84 (adults) and 8.43 (children) in the dry season. Summed Incremental Lifetime Cancer Risk reached 3.95 × 10⁻³ (adults) and 1.18 × 10⁻² (children), both exceeding the USEPA upper acceptable bound of 1 × 10⁻⁴. Cadmium contributed 81.3 percent of total carcinogenic risk.

Conclusion, Household waste disposal practices in Okene are causing significant groundwater contamination that poses unacceptable carcinogenic and non-carcinogenic health risks, particularly to children. Urgent policy interventions are required encompassing formalised waste management infrastructure, enforced dumpsite exclusion zones, and routine groundwater quality monitoring under NESREA and Kogi State regulatory frameworks.