ORIGINAL PAPER Multivariate statistical analyses of the groundwater system in Darb El-Arbaein, Southwestern Desert, Egypt Mohamed El Kashouty & Aiman Abdel-Lattif # Saudi Society for Geosciences 2010 Abstract In Darb El-Arbaein, the groundwater is the only water resource. The aquifer system starts from Paleozoic– Mesozoic to Upper Cretaceous sandstone rocks. They overlay the basement rocks and the aquifer is confined. In the present research, the performance of the statistical analyses to classify groundwater samples depending on their chemical characters has been tested. The hydro- geological and hydrogeochemical data of 92 groundwater samples were obtained from the General Authority for Rehabilitation Projects and Agricultural Development au- thority in northern, central, and southern Darb El-Arbaein. A robust classification scheme for partitioning groundwater chemistry into homogeneous groups was an important tool for the characterization of Nubian sandstone aquifer. We test the performance of the many available graphical and statistical methodologies used to classify water samples. R- mode, Q-mode, correlation analysis, and principal compo- nent analysis were investigated. All the methods were discussed and compared as to their ability to cluster, ease of use, and ease of interpretation. The correlation investigation clarifies the relationship among the lithologic, hydrogeo- logic, and anthropogenic factors. Factor investigation revealed three factors, namely, the evaporation process– agricultural impact–lithogenic dissolution, the hydrogeo- logical characteristics of the aquifer system, and the surface meteoric water that recharge the aquifer system. Two main clusters that subdivided into four subclusters were identi- fied in the groundwater system based on hydrogeological and hydrogeochemical data. They reflect the impact of geomedia, hydrogeology, geographic position, and agricul- tural wastewater. The groundwater is undersaturated with respect to most selected minerals. The groundwater was supersaturated with respect to iron minerals in northern and southern Darb El-Arbaein. The partial pressure of the groundwater versus saturation index of calcite shows the gradual change in PCO 2 from atmospheric to the present aquifer pressures. Keywords Groundwater samples . Groundwater chemistry . Multivariate analysis . AquaChem . Egypt Introduction The groundwater represents a resource for multiple uses (General Authority for Rehabilitation Projects and Agricul- tural Development (GARPAD) 1998–2001). They irrigate 12,000 feddans (1 feddan ≈ 1.038 acres) and help 16 villages for farmers along about 400 km from Paris town towards the Egypt–Sudan border. The pumping wells are located in three parts: the northern, the central, and the southern part of Darb El-Arbaein (Fig. 1). The northern part extends 90 km to the south from Paris town and has an area of 90 km 2 . The central part extends 80 km to the south of the northern part and has 120 km 2 in area. The southern part extends 200 km to the south of the central part and has 170 km 2 in area. The Darb El-Arbaein is located in an arid M. El Kashouty Faculty of Science, Geology Department, Cairo University, Cairo, Egypt A. Abdel-Lattif (*) National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt e-mail: aiman_aziz21@yahoo.com DOI 10.1007/s12517-010-0123-4 Arab J Geosci (2011) 4:1117–1130 Received: 10 November 2009 / Accepted: 12 January 2010 / Published online: 23 February 2010