Environmental and geophysical implications of landfill leachate plumes on groundwater, uppermost topsoil, and engineering foundations

Landfills remain the most widely adopted cost-efficient waste management systems across the globe. However, the infiltration of the landfill leachate plumes emerging from hazardous materials within poorly managed landfill sites remains a significant threat to groundwater resources and civil/environmental engineering foundations, especially in developing nations like Nigeria. To address these concerns, this study assesses the impact of landfill leachate plumes (LLPs) on groundwater, topsoil, and engineering foundations in Kaduna, Nigeria. The objectives of this study include delineating subsurface contamination using geophysical methods, analyzing the physicochemical and heavy metal content of leachate, and evaluating associated environmental and geotechnical risks. Integrated geophysical and laboratory analyses were employed. Electrical Resistivity Tomography (ERT) surveys (5 profiles) and ground magnetic surveys (24 lines) were conducted using an ABEM SAS4000 and an ENVI PRO magnetometer. Data were processed using RES2DINV and Oasis Montaj software. Leachate samples were analyzed via Atomic Absorption Spectrometry to determine heavy metal concentrations (Pb, Cd, Zn, Fe, and Cr), as well as BOD₅, COD, TDS, and EC. ERT results identified severely contaminated zones within the landfill, with resistivity values ranging from 2.8 to 9.0Ωm compared to 29 - 150Ωm off-site areas of depths at 0 - 3.5m. Magnetic surveys revealed anomalies from 31095 to 43510nT, correlating with leachate accumulation at 2 - 5m. Hydrochemical analysis showed high heavy metal concentrations (11.17-21.73 mg/L), elevated BOD₅ (809 mg O_2/L) and COD (2104 mg O_2/L), and a BOD₅/COD ratio of 0.385, indicating the presence of biodegradable organic matter. The LLPs contributed significantly to groundwater contamination and the depletion of the supportive topsoil layer. The combined geophysical and hydrochemical methods successfully identified the extent of contamination. The study clearly shows the importance of proper landfill lining, soil treatment, and effective waste management practices in developing countries to safeguard both infrastructural and health conditions. Future study could focus on simulation modeling of contaminant transport.