Potential Impacts of Okpuno Egbu Dumpsite on Groundwater Resources in Parts of Nnewi, Southeastern Nigeria

Abstract

The study area, Nnewi is one of the most populated, commercial and industrialized cities in Anambra State. Geophysical data were collected from 15 vertical electrical sounding (VES) points and hydrogeochemical analysis of 15 groundwater samples collected from 15 locations were analyzed for their chemical composition and used to assess the impact of the dumpsite at Okpunoegbu on groundwater in the study area. The results of the vertical electrical sounding indicate that most of the aquiferous units fall within the fourth layer at most of the Relocations with an average resistivity of 1340.25Ωm, an average thickness of 41.75m and average depth of 51.25m. The range of the regional water table is from 25.41m to 99.42m. The Dar-Zarrouk parameters; longitudinal conductance and transverse resistance, s and t were determined from the geophysical data to be 0.007mho and 55966.9Ω respectively. The results of s indicate that the protective capacity of the overburden layers to underlying aquifer is low. which implies easy transmission of pollutants to the aquifers making them vulnerable to pollution. The results of water analysis show that the range of pH in the samples is between 5.73 to 6.95 indicating that 20% of the water samples are slightly acidic and 80% to alkaline. TDS, TSS and EC were found to be within the permissible limits of WHO and NSDWQ standard guidelines. COD and BOD were above the permissible limits indicating the water samples to be severely polluted. DO1 and DO5 range between 22.78 - 65.40 mg/L and 48-358.96 mg/L respectively. The major cations and anions were within the permissible limits.. However, the heavy metals range in samples were cadmium (0.04-0.37mg/L), chromium (0.01-0.10mg/L), mercury (0-0-07mg/L) and lead (0.1-0.93mg/L), exceed the permissible limits in some samples. The geospatial distribution maps of the heavy metals implicate the dumpsite and other sources as contributors of the increased concentrations of cadmium and lead. while indicating the dump as a major contributor of chromium and mercury to groundwater in the study area. The calculated quality indices, WQI and HMPI rate the groundwater as highly polluted and unsuitable for drinking, and the CD and HMEI as moderately to highly polluted, respectively. The identified hydrochemical facies classify the water as Ca-Cl and Ca-Mg –Cl – SO4 water type. The Cl – SO4 facie indicate end water usually with increased age found in the discharge areas. The Okpunoegbu dumpsite is an important source of groundwater contaminants and pollutants especially the heavy metals such as cadmium, mercury, chromium and lead. The protective capacity of the overburden is enhancing the vulnerability of the aquifers to pollution as they are rated as low. It is recommended that some remediation measures be carried out to restore the groundwater quality and prevent further pollution being initiated and appropriate water treatment be carried before use for drinking purposes.