Delineating Subsurface Sewage Flow Path through Directional Fracture Identification in Parts of Owo Area, Southwestern Nigeria

Abstract

The disposal of waste materials by burial is the oldest form of solid waste disposal. A major concern with the usage of traditional dump sites is the potential of polluting groundwater. The pollution could be metals, microbes or other substances. This problem of groundwater contamination from refuse disposal especially those located uphill are worsened when communities that rely on dump site disposal system also depend on private wells for drinking water. Wastewater often makes its way into other water bodies. Water runoff from rain may wash contaminants into the surface waters. A more significant hazard is when pollutants from the drain field move quickly through the soil and potentially into the groundwater making the supposed potable water unusable. The application of methods involving identification of anisotropic behavior and heterogeneities in rocks has become increasingly acceptable because these methods provide adequate knowledge about the presence of fractures and their directions. Observed changes in apparent resistivity with azimuth are typically used for such interpretation which indicates fracture anisotropy. Due to repeated cases of groundwater pollution in the area, this study researches into the application of surface geophysical methods to detect bedrock fractures and to estimate hydraulic properties of the fractured bedrock in order to determine the direction of  wastewater flow from a dump site located uphill into a public  borehole. Azimuthal Square array was used to detect fractures in bedrock in parts of Owo area in Ondo State, Nigeria. Apparent resistivities measured at four locations near the dumpsite changed with the orientation of the array. Scattered plots and Graphical interpretation of the technique indicate that a dominant fracture set is oriented NW/SE. Hydrochemical analysis of water samples collected from three hand dug wells around the dump revealed presence of leachates. The presence and interconnectivity of fracture zones in almost all the sampled points even at the over burden in the study area provide pathway for easy movement of the waste water.