Assessment of Groundwater Vulnerability to Open Dumpsites and the Associated risk using Geophysical and Geochemical Approach

An integrated geophysical and geochemical study was conducted to assess the impact of an open dumpsite on groundwater in part of Lokoja, Nigeria. The investigation employed three 2D resistivity profiles, three Induced Polarization (IP), distributed around the dumpsite, 200 m and 400 m west of the dumpsite respectively, six Vertical Electrical Sounding data and four groundwater samples for physiochemical analysis, distributed around the dumpsite and at 200 and 400 m. Data interpretation using RES2DINV, WINRESIST, and EXCEL revealed geoelectric layers, groundwater conditions, and potential contamination zones. Results from 2D resistivity and IP profiles at the dumpsite indicated low resistivity (7.42–19.3 Ωm) and chargeability (<1 msec) to a depth of 17.4 meters, suggesting contamination in the topsoil and fractured basement zones. Profiles at 200m and 400 m west showed moderate resistivity (50–800 Ωm) and chargeability (<1–3 msec), reflecting better groundwater quality. Physiochemical analysis of water samples at the dumpsite revealed slightly acidic pH (6.2–6.4), elevated TDS (1275–1713 mg/l), EC (2.28–2.31 mS/cm), COD (20.6–21.3 mg/l), BOD (5.6–5.8 mg/l), and lead (0.0137–0.0143 mg/l), exceeding WHO standards. Samples from 200m and 400 m west of dumpsite generally met WHO limits, except for TDS, EC, and COD at 200 m. The study reveals that the dumpsite's leachate plume has not significantly affected groundwater quality westward, likely due to groundwater flow direction or delayed migration. However, observed geochemical and geophysical anomalies around the dumpsite and 200 m west, indicate potential future contamination, emphasizing the need for immediate mitigation