Hydrochemical Facies and Ionic Ratios of the Coastal Groundwater Aquifer of Saudi Gulf of Aqaba: Implication for Seawater Intrusion Awni Batayneh † , Haider Zaman ‡ , Taisser Zumlot † , Habes Ghrefat † , Saad Mogren † , Yousef Nazzal † , Eslam Elawadi † , Saleh Qaisy † , Ibrahim Bahkaly † , and Ahmed Al-Taani § † Department of Geology and Geophysics King Saud University P.O. Box 2455 Riyadh 11451, Saudi Arabia awni@ksu.edu.sa ‡ Department of Geology Taibah University P.O. Box 30002 Madinah 41477, Saudi Arabia § UNESCO Chair for Desert Studies and Desertification Control Yarmouk University Irbid 21163, Jordan ABSTRACT Batayneh, A.; Zaman, H.; Zumlot, T.; Ghrefat, H.; Mogren, S.; Nazzal, Y.; Elawadi, E.; Qaisy, S.; Bahkaly, I., and Al- Taani, A., 2014. Hydrochemical facies and ionic ratios of the coastal groundwater aquifer of Saudi Gulf of Aqaba: implication for seawater intrusion. Journal of Coastal Research, 30(1), 75–87. Coconut Creek (Florida), ISSN 0749-0208. It is now fairly documented that major ion chemistry of the groundwater can be used to determine an interaction between the groundwater and saline water in the costal aquifers, and that there exists a relationship between total dissolved solids and Cl  , Na þ , Mg 2þ , and SO 2 4 concentrations of groundwater. This hypothesis is tested on an aquifer located along the Saudi Gulf of Aqaba coast (Red Sea). Groundwater samples collected from 23 locations show the abundance of ions in the order of: Ca 2þ . Na þ . Mg 2þ . K þ ¼ Cl  . SO 2 4 .HCO  3 . NO  3 . The Piper trilinear diagram reveals two dominant clusters, i.e. the Ca 2þ –Cl  –SO 2 4 facies and the Na þ –Cl  –SO 2 4 facies. Besides the major chemical compositions, ionic ratios (HCO  3 /Cl  , Na þ /Ca 2þ , Na þ /Cl  , Ca 2þ /Cl  , Mg 2þ /Cl  ,K þ /Cl  , SO 2 4 /Cl  , Ca 2þ /Mg 2þ , Ca 2þ /SO 2 4 , and Ca 2þ /HCO  3 ) are used to evaluate the effects of saline water intrusions. Factor analysis of the studied samples demonstrates that changes in the groundwater composition are primarily controlled by mineral dissolution, human activities, weathering of marine sediments, evaporation/salinization of groundwater, and the residence time of water. An attempt has been made to identify hydrochemical processes accompanied with the current intrusion of seawater through the use of ionic exchanges. Following this procedure, about 7.97% mixing rate of seawater intrusion has been estimated for the month of March 2012. Furthermore, the seawater mixing index has also been applied, which resulted in a range of values from 0.395 to 7.922. These results determine 13 of 23 groundwater samples (57%) as saline, with electrical conductivity . 3000 lS/cm. ADDITIONAL INDEX WORDS: Groundwater interaction, seawater interaction, hydrochemistry, factor analysis, ionic exchange, SMI, Saudi Arabia. INTRODUCTION Salinization of fresh groundwater aquifers is a common problem in most of the coastal areas around the world (Al-Agha and El-Nakhal, 2004; Barker, Newton, and Bottrell, 1998; Batayneh, 2006; Batayneh, Elawadi, and Al-Arifi, 2010; Mondal et al., 2010; Nwankwoala and Udom, 2011; Silva-Filho et al., 2009). This phenomenon can be attributed to several reasons like gentle coastal hydraulic gradients, low infiltra- tions, excessive pumping, and local hydrogeological conditions. During the past few decades, researchers produced several publications on the subject from different areas of the world (Diamantis and Petalas, 1989; Kim et al., 2009; Lee and Song, 2007a; Melloul and Collin, 2006; Mondal et al., 2008; Sarma and Krishnaiah, 1976). The study area, located along the eastern cost of Saudi Gulf of Aqaba, is not immune from the effect of seawater intrusion. In addition to the needs of the local population, an increase in the number of tourists (mainly during summer season) has increased a demand for water in the Gulf of Aqaba coast. So far no study has been done to examine hydrochemical behavior of the groundwater in this area; an attempt has been made through this study to evaluate the types of water and their hydrogeochemical characteristics in the target area. The main ionic processes governing the quality and composition of groundwater in the aquifer system of the area is also assessed. Furthermore, the study will help in establishing a basis for an appropriate monitoring system and eventually an improved management of the groundwater resources in the area. To achieve the above objectives, the following tasks are carried out: (1) analysis and interpretation of different data sets to discriminate the effects of different hydrochemical processes; (2) principal component analysis (PCA) for separation of groundwater samples from natural hydrochemical behavior; (3) calculation of ionic deviations to better understand the DOI: 10.2112/JCOASTRES-D-13-00021.1 received 27 January 2013; accepted in revision 7 April 2013; corrected proofs received 12 May 2013. Published Pre-print online 5 June 2013. Ó Coastal Education & Research Foundation 2014 Journal of Coastal Research 30 1 75–87 Coconut Creek, Florida January 2014