Groundwater and Aquifer Depth Estimation: a Case Study of Futo and Its Environs in Owerri West L.g.a, Imo State

This study aims to investigate the groundwater potential and aquifer characteristics within the Federal University University Owerri (FUTO) and its environs in Owerri West, Imo State. The research involves application of geophysical methods, specifically vertical electrical sounding (VES), to determine the depth and resistivity of subsurface layers. The findings were analyzed using Zond software, which provided detailed resistivity profiles and stratigraphic interpretations. The results highlighted significant variations in aquifer depths and properties, essential for effective groundwater management. The study contributes to the understanding of the groundwater system in the area and supports informed decision-making for water resource development and management. 1.1 Background of the Study Vertical Electrical Sounding (VES) or Geo-electrical survey is commonly known in environmental or engineering prospecting. Geophysical studies which provide nondestructive methods have recently been employed to reduce cost and numerous problems. With advantages of non-invasive, low cost and fast, geophysical method always become as a primary solution in various exploration. One of the common problems engineering field would be soil erosion due to water movement either on the surface or beneath the surface. In general, soil erosion can be defined as one form of soil degradation along with soil compaction, low organic matter, and loss of soil structure, poor internal drainage, salinization, and soil acidity problems. Due to the changes of the properties and behavior of the soil, therefore, it can influence both construction operations and the performance of competed construction. Hence, geo-electrical survey would be appropriate tool as it is most likely measured the changes of resistivity (or conductivity) which is one of the most important physical properties of the soil. In the evaluation of groundwater potential, the geophysical method used in the resistivity survey. Resistivity methods are extensively used by geophysicist for the evaluation of deep subsurface. The resistivity method measures the apparent resistivity of the subsurface including the effects of any or all the following: soil type, bedrock, fractures, contaminants of groundwater variation in electrical resistivity may indicate changes in composition, layer thickness or contaminant levels, the resistivity method is useful for simultaneously detecting lateral and vertical changes in the subsurface electrical properties. Data were acquired at electrode stations spaced along survey lines. Our digital field data recording capability allows us to collect and interpret data both rapidly and accurately. There are several electrode array geometries that we are capable of employing, but our preferred method is the Vertical Electrical Sounding to produce a high quality data set suitable to most applications. The Vertical Electrical Sounding (VES) plays a satisfactory role in groundwater investigation. This method of surveying is the most versatile, easy to use and successful geophysical prospecting methods ever created. The objective of most Vertical Electrical Sounding (VES) is to obtain true resistivity models for subsurface. The determination of the subsurface distribution of resistivity from the measurement on the surface can yield useful information on the structure or composition of buried formation (Dobrin, 1976). The target of any geophysical exploration is to non-intrusively gather information about the subsurface or any other medium under investigation (Scollar, 1990). Indeed, the flux of electrical charges through materials permits conductor materials like metal or electrolytes, whose conductivity is great, to be distinguished from less conductive and insulating materials like ice, gas, oil etc that exhibit high resistivity. However, soil materials exhibit intermediate electrical properties depending on their physical and chemical properties (texture, mineralized fluid, salinity, or water content). Geo-electric modeling based on the geophysical characteristics of soil with depth is a dependable tool for lithology characterization. Every geo-electric layer has its own peculiar electrical properties, depending on its physical and chemical conditions. A good knowledge of stratigraphy can help in the understanding of the layers of the subsurface with respect to the strength of the soil for construction purposes, electrical earthing, environmental assessment and groundwater resource exploration. Schlumberger array was adopted owing to its ability to effectively delineate small intervals of soil horizons with comparably less length of spread, less labour, relatively less cumbersome and gives better results in the study area compared to other geophysical methods. 1.2 Statement of the Problem Municipal areas are mostly dependent on groundwater for agricultural, industrial and domestic purposes. The accurate estimation of groundwater and aquifer depth is essential for sustainable water resource management. This study focuses on Federal University of Technology Owerri (FUTO), and its environs in Owerri West, Imo State. The region has experienced significant urbanization and population growth, increasing the demand for reliable groundwater resources. Rapid urbanization and development in the study area have altered the natural recharge and discharge patterns of groundwater. The construction activities and land use changes can significantly affect the groundwater levels and aquifer recharge rates. This has raised the need for the delineation of the ground water potentials within the region into their bearing capacities in order to support groundwater infrastructural development and instill confidence back in the minds of the funding agencies, implementing institutions and the communities of water projects in the region. The complexities associated with the inter-linkages between population and the environment is manifested by resources utilization. Water is the most precious and commonly used resource in nature. It is essential for survival and sustenance of life and environment. The demand for clean water supply has also become an indicator of the quality of life in a society. It is related to health issues, environmental issues, etc. Hence, one of the most natural resources to be given due consideration in developmental issues, industrial, agricultural, settlement, town planning etc. is the supply of adequate and sustainable water meeting the required standards. Therefore, the need for groundwater and aquifer depth estimation is a necessity for sustainable quality water management 3.2 Methods This study used the electrical resistivity method to investigate the parameters of the subsurface structures of the study area. The Terrameter Signal Averaging System (SAS) model 300B and its accessories were used to carry out the vertical electrical sounding. A total of five (5) VES were sounded and with a total spacing of 100m and the Schlumberger array pattern with half inter electrode spacing (AB/2) ranging from 1-125m was adopted. Through a pair of current electrodes A and B, direct current (DC) was supplied into the ground and the potential difference was measured by means of another pair electrodes M and N called the potential electrodes. Data Presentation For this research, the delineation of geo-electric layers and thickness were done with the Zond software, while the geological units were delineated based on geo-electric resistivity range of lithology and the knowledge of the geology of the study area. The results of the investigation are presented in the table 4.1, sounding curves and geo-electric section below. Table 4.1 below shows the geo-electric layer parameters deduced from computer iteration and modeling of the VES curves gotten from the study area. The model curve types deduced are: H, K, KH curve types. The result of the twenty one (21) VES points carried out and in five (5) various locations in FUTO and its environs in Owerri West to determine the groundwater occurrence and aquifer depths in the study area are discussed in this research work. 4.2 Data Analysis and Results The Vertical Electrical Sounding (VES) data interpretation started by first plotting the apparent resistivity computed form the first measurements versus half current electrode spacing in a resist software environment. The sounding curve is then compared with the internally built standard curves generated by the software program, to obtain the parameters of the geo-electric layers in terms of layer resistivity, depth and thickness. The field data computed and results obtained in twenty one (21) VES points in five (5) various locations. In each location, twenty one (21) VES points were conducted and this revealed three (3) to four (4) layers within the study area. The distribution of resistivity of different subsurface layers in a four (4) layered earth model can be classified based on curved shapes/types into type K (ρ1ρ3), type H (ρ1>ρ2