Forensic magneto-electrical resistivity and hydrochemical characterization of dumpsite-affected areas and its implications for groundwater quality and public health risks

Unlined dumpsites embedded within residential districts remain one of the greatest environmental challenges, threatening shallow groundwater and public health. This study characterizes selected active and non-engineered dumpsites across Kaduna metropolis in Nigeria through a forensic integration of ground magnetic surveying (GMS), electrical resistivity tomography (ERT), and hydrochemical analysis. A total of 525 GMS stations and 2D ERT sections were acquired at two dumpsites at two dumpsites, and a hydrochemical analysis of 25 proximal water sources (hand-dug wells and rivers) across 10 dumpsites. Euler deconvolution (SI = 1) placed buried ferromagnetic waste between 1.2 and 10.0 m, while the ERT sections resolved conductive leachate plumes (≤ 15 Ωm) spanning 0.5–6.5 m depths that intersect the shallow weathered-gneiss aquifer directly rather than merely approach. Each sample breached WHO and NSDWQ drinking limits for iron (0.33–2.42 mg/L) and lead (0.16–1.92 mg/L), with lead contamination factors reaching 192. Rivers carried a heavier burden than the wells, and BOD₅/COD ratios of 0.32–0.75 indicate organic loads still actively degrading rather than stabilized. Hazard indices of 1.45–17.34 for adults and 3.08–36.78 for children were dominated almost entirely by lead, which accounted for approximately 99% of the non-carcinogenic risk. No sampled source is suitable for consumption, and the exposures implied for children fall squarely within the range associated with health risk. The agreement between magnetic source-depth envelopes, resistivity plume pathways and measured toxicity provides an empirical basis for enforced setback distances, minimum well-depth regulation, and targeted lead surveillance in basement-complex urban environments.