VOL. 13, NO. 9, MAY 2018 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2018 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 3063 HYDROGEOCHEMISTRY AND QUALITY ASSESSMENT OF SHALLOW GROUNDWATER IN THE COASTAL AREA OF IGBOKODA, SOUTHWESTERN NIGERIA A. O. Talabi Department of Geology, Ekiti State University, P. M. B., Ado-Ekiti, Nigeria E-Mail: abel.talabi@eksu.edu.ng ABSTRACT Hydrogeochemistry and quality assessment of shallow groundwater was carried out at Igbokoda coastal area, Southwestern Nigeria to ascertain its potability and suitability for agriculture. Twenty groundwater samples collected from the area were analyzed for cations and anions employing the Buck Scientific Model 210VGP Atomic Absorption Spectrophotometer and colorimetric method respectively. Temp (°C), pH and EC (μS.cm) were measured in-situ using multiparameter portable meter. Sodium absorption ratio, residual sodium bi-carbonate, permeability index, magnesium absorption ratio and Kelly ratio were estimated from the chemical data. Piper diagram, Principal component and correlation analyses were employed to reveal the hydrogeochemical characteristics of the shallow groundwater. The abundance of the major ions was; Na + >Ca 2+ >K + >Mg 2+ and Cl¯ > SO 4 2 ¯ >HCO 3 ¯ >NO 3 - . The major hydrochemical facieses were Na-Cl, Ca-Cl and mixed Ca–Mg–Cl types while precipitation and rock-water interaction constitute the major processes controlling the groundwater chemistry. All ionic concentrations were within approved standards for drinking water. However, 85% of the groundwater samples tested positive to e-coli counts. Evaluated irrigation parameters showed that the groundwater has a low to medium salinity hazard, low alkalinity hazard, magnesium absorption ratio, sodicity and Kelly ratio. This study revealed a non potable groundwater system that is suitable for agriculture. Keywords: potability, irrigation quality, hydrochemical facieses, piper diagram, e-coli counts. 1. INTRODUCTION Igbokoda is strategically located. It is the head quarter of the oil rich Ilaje local government and the gateway to other towns in the area. Igbokoda is famous as the hub of economic and commercial activities within Ondo State and beyond because it has the largest fish terminals in Nigeria in addition to oil palm production, alcohol distillery and palm wine tapping industries. The town is fluxed with migrants due to ongoing exploration for oil in the local government area. Igbokoda coastal zone is within the eastern part of Dahomey sedimentary basin and is endowed with abundant important raw materials including the high quality silica sand that is used in glass sheet production, crude oil that constitute the main source of revenue for Nigeria as well as large deposit of untapped bitumen. People in this area depend mainly on groundwater for drinking, agriculture and industrial uses. Groundwater is essential for continuity of life on earth and its occurrence is a function of different factors including geology, relief, type and amount of vegetative ground cover, seawater intrusion, anthropogenic activities and most importantly in recent time climate change [1]. In addition, the variation in the chemical composition of groundwater in coastal region depends on the nature of the hydrogeology, hydrometeorology, topography, drainage and other artificial conditions [2]. Climate change in combination with increased anthropogenic activities will affect coastal groundwater systems throughout the world [3]. Groundwater constitutes a portion of the hydrologic cycle. In the natural hydrologic cycle, human activities have induced many negative effects on the quality of groundwater resulting into artificial degradation of natural groundwater quality which can impair the use of water and create hazards to public health. The intensive use of natural resources and the large production of wastes in the study area often pose a threat to groundwater quality and could result into groundwater contamination. Igbokoda is densely populated because it has over the past decades, witnessed an unprecedented increase in the rate of development. Throughout the area, there are many human activities that have the potential to discharge pollutants into the environment which can then infiltrate into the groundwater resources. Indeed, groundwater withdrawal in the coastal area of Igbokoda beyond its renewable capability is not negotiable. The extensive exploitation of groundwater results in groundwater storage depletion, lowering of the water-table (drawdown), seawater intrusion and associated freshwater problems in the coastal region [4, 5]. Humans and plants existence and sustainability/continuity depend on water that has sufficient quality to serve as drinking water (potable water), an essential ingredient for good health and the socio-economic development of man [6]. Over large parts of the world, humans have inadequate access to potable water and use sources contaminated with disease vector, pathogens or unacceptable levels of toxins or suspended solids [7]. Such water is not wholesome and drinking or using such water in food preparation leads to widespread acute and chronic illness and constitute a major cause of death and misery in many countries [8]. Hence, this study examined the Hydrogeochemistry and groundwater quality of the coastal area of Igbokoda with a view to identify the mechanisms responsible for the chemical compositions of the shallow