Electrical Resistivity and Hydrogeochemical Evaluation of Septic-Tanks Effluent Migration to Groundwater

Water quality degradation through different kinds of pollutants is a major concern globally. Hence, this study becomes imperative in order to determine the effects of groundwater pollution due to septic tank effluent. Integrated electrical resistivity imaging, physicochemical and microbiological analyses of water samples from ten hand-dug wells (HdW) and three boreholes (BH) were carried out around residential areas surrounded by septic tank systems using standard field and laboratory procedures. Results of the 2-D resistivity imaging of the subsurface along nine traverses around the study area using Wenner configuration with constant electrode separation ranging from 2 to 12 m showed anomalously low resistivity zones, less than 20 Ωm suspected to be septic plume accumulation. The accumulation was more pronounced in the northern and southern part of the study area to a depth of about 10 m. The direction of groundwater flow suggests that the water in the wells is flowing towards the direction of the septic plume. Physicochemical analyses showed the groundwater samples to be within the specified limits of WHO/NSDWQ for drinking purpose. However, higher values of concentrations of most analyzed parameters were noticed in HdW 6 and HdW 7 due to their nearness to septic tank system. The microbiological analysis indicates excessive amount of microbes in the samples, an indication of groundwater contamination by effluent from the septic tanks. The study recommends treatment and regular monitoring of groundwater sources, adequate distance from water sources to septic systems and adoption of clean technology to prevent contamination of groundwater flow.