Geophysical research on the interplays between soil-rock variability and hydrogeological structures: a case study

Understanding the spatial variations in soil-rock profiles is crucial for identifying weathered rock layers and mapping geological structures, particularly in the complex feldspar-rich granitic terrain of Penang Island, Malaysia. This study employs a combination of electrical resistivity and seismic refraction tomographic techniques, along with borehole lithological data, in three distinct areas on the island. Its goal is to provide insights into surficial and subsurface soil-rock properties and water-bearing structures within the North Penang Pluton (including a part of the Sungai Ara axis) for sustainable groundwater development, addressing the region's growing population's needs. The research identifies three distinct geological units near the surface: residual soils, highly to moderately weathered/fractured granitic layers, and fresh bedrock, each with its hydrogeological properties. Promisingly, the weathered layers offer significant groundwater development potential, with deep-weathered and potentially fractured zones exceeding 30 meters in the study area. These findings have substantial implications for sustainable groundwater development, especially in tropical hard-rock terrains. Additionally, the study underscores the limitations of small geophysical spacings for probing deeper groundwater resources. This knowledge is essential for informed decision-making in water resource management and infrastructure development, addressing the ongoing global challenge of ensuring access to clean water resources amid population growth.