Effects of Leaking Septic Tanks on UndergroundWater Quality in Owerri Municipal, Imo State, Nigeria

摘要

Aim: To determine the effects of leaking septic tanks on underground water quality in Owerri Municipal.Place and Duration of the Study: Department of Geosciences, Federal University of Technology Owerri, and Department of Chemistry, Alvan Ikoku University of Education, Owerri, Imo State, Nigeria, between January 2013 to May 2014.Methodology: Geophysical and geochemical analysis was carried out using chemical and geophysical analyses. Owerri Municipal is located within Longitudes 6º59’E to 7º06’E and Latitudes 5º33’N. It falls within the coastal plains sands. The quality of groundwater was determined by taking samples from three locations namely Amakohia, Naze and Nekede and carrying out physiochemical analysis on each to ascertain the nature of dissolved substances in the groundwater. Also, physiochemical parameters like bulk density, porosity and permeability of the samples were determined. Description of the lithology and aquifer parameters were obtained using vertical electrical sounding method.Results: The density of the samples ranged from 1.49 to 1.98 mg/L, the porosity values are from 0.20 to 0.38 while the permeability varies from 0.51 mg/L to 0.67 mg/L.The chemical analysis revealed that some heavy metals have concentrations above the amount acceptable by WHO standards. Iron 18.6 to 63.9 mg/L, Nickel 7.5 mg/L and Manganese, 0.46 mg/L. The resistivity of the topsoil ranges from 618 Ωm to 3800 Ωm. An average resistivity range of 7500 Ωm exist up to 30 m while a layer of low resistivity indicating clay and clayey sand extends to 60 m at Naze, 60 m at Nekede and 50 m at Amakohia. Beyond these depths, the resistivity is high on the average of 3500 Ωm.Conclusion: The results showed that the subsurface is permeable which implies that traces of heavy metals present in the samples are contained in the leachets from surrounding environments either from septic tanks or from industrial activities on the surface. Groundwater quality can be improved within this environment by recommending boreholes drilled from 70 m where leachet permeability is negligible.