ABSTRACT:

Drilling for groundwater is expensive and challenging. It is even more challenging to find a location that will result in a high yield well in heterogenous environments. To tackle the heterogeneity issue, geophysical surveys can help to map the subsurface structure and help delineate the trajectory of drilling. This study displays the effectiveness of 3D Electrical Resistive Tomography (ERT) to locate permeable groundwater zone within a highly heterogenous subsurface. Ground truthing the acquired geophysical data with in-situ sampling helps to ensure accuracy in classifying groundwater zones in the final inverted 3D dataset while also delineating boundaries between permeable groundwater zones and clayey structures (from well data). In-situ sampling includes groundwater and soil sampling, where laboratory testing of both samples allows for this correlation. Clay zones in the dataset are classified from the nearby well data at similar depth range and from very low resistivity values after ERT data processing and laboratory measurements. The results display highly differentiating resistivity zones that are attributed to the scattered clay lenses (low resistivity) in conjunction with the freshwater zone (high resistivity). The distinction between clay and groundwater bodies is important to better inform drilling location for optimal groundwater yield. This study concludes that with the aid of low-cost geophysical surveys, and minimal in-situ sampling data correlations, groundwater boundaries and clay lens volumes can be identified easily.