EARTH SCIENCESRESEARCH JOURNAL

Earth Sei. Res. J. Vol. 13, No. 2 (Deeember 2009): 166-182

STATISTICAL INVESTIGATION OF THE GROUNDWATER SYSTEM INDARB EL-ARBAEIN, SOUTHWESTERN DESERT, EGYPT

Abdel-Lattif. A. ' and Mohamed El Kashouty^' National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt.

^ Cairo university. Faculty of Science, Geology Department

ABSTRACTIn Darb El Arbaein, the groundwater is the only water resources. The aquifer system starts from Paleozoic-Mesozoic to UpperCretaceous sandstone rocks. They overlay the basement rocks and the aquifer is confmed. In the present research, the perfor-mance of tbe statistical analyses to classify groundwater samples depending on their chemical characters has been tested. Thebydrogeological and hydrogeocbemical data of 92 groundwater samples was obtained from tbe GARPAD authority in nortbern,central, and southem Darb El Arbaein. A robust classification scbeme for partitioning groundwater chemistry into homoge-neous groups was an important tool forthe characterization of Nubian sandstone aquifer. We test the performance of tbe manyavailable graphical and statistical methodologies used to classify water samples. R-mode, Q-mode. correlation analysis, andprincipal component analysis WCTQ investigated. All the methods were discussed and compared as to their ability to cluster,ease of use, and ease of interpretation. Tbe correlation investigation clarifies the relationship among tbe Uthology,bydrogeology, and anthropogenic. Factor investigation revealed three factors namely; the evaporation process-agriculturalimpact-lithogenic dissolution, the hydrogeological characteristics of tbe aquifer system., and tbe surface meteoric water that re-charge tbe aquifer system. Two main clusters tbat subdivided into four sub clusters were identified in groundwater systembased on bydrogeological and hydrogeochemical data. They reflect the impact of geomedia, hydrogeology, geographic posi-tion, and agricultural wastewater. The groundwater is undersaturated with respect to most selected minerals. The groundwaterwas supersaturated with respect to iron minerals in northern and southem Darb El Arbaein. The partial pressure of COi of tbegroundwater versus saturation index of calcitc shows the gradual change in PCO2 from atmospheric to the present aquifer pres-sures.

Keywords: Groundwater samples, groundwater cbemistry, Multivariate analysis, AquaChem. Egypt, Darb El-Arbaein.

RESUMENEn Darb El Arbaein, el agua subterrnea es el nico recurso bidrco. El sistema acuifero confinado incluye rocas delPaleozoico-Mesozoico hasta areniscas del cretcico superior sobre el basamento. En esta investigacin se prob el desempeodel anlisis estadistico para clasificar las muestras de agua subterrnea en fiincin de sus caracteristicas qumicas. Datoshidrogeolgicos e hidrogeoquimicos de 92 muestras de agua subterrnea fueron obtenidas en el norte, centro, y sur de Darb ElArbaein. Se us un esquema de clasificacin robusto para separar quimicamente en grupos bomogneos las aguassubterrneas del acuifero de la arenisca de Nubia. Se probaron los rendimientos de varias metodologias grficas y estadisticas

Manuscript received: 8/10/2009Accepted for publication: 20/12/2009

166

STATISTICAL INVESTIGATION OF THE GROUNDWATER SYSTEM IN DARB EL-ARBAEIN. SOUTHWESTERN DESERT. EGYPT

para clasificar las muestras de agua, entre ellas anlisis de correlacin, modo R, modo Q y componentes principales. Lascorrelaciones aclaran las relaciones entre la litologia, la hidrogeologia y la influencia antropognica. La investigacin reveltres factores a saber: evaporacin asociada a procesos agrcolas e impacto de disolucin litognica, las caracteristicashidrogeolgicas del acuifero, y la superficie meteorizada por donde se recarga el acuifero. Se identificaron dos gruposprincipales subdivididos en cuatro subgrupos que reflejan el impacto de la geologia. hidrogeologia, posicin geogrfica, y lasaguas residuales agrcolas. El agua subterrnea es insaturada con respecto a la mayoria de los minerales seleccionados perosobresaturada con respecto a los minerales de hierro en el norte y el sur de Darb El Arbaein. La presin parcial del aguasubterrnea en relacin al ndice de saturacin de calcita muestra un cambio gradual en PCO2 de la presin atmosfrica a lapresente en el acuifero.

Palabras clave: Muestras de las agua subterrnea, qumica de las aguas subterrneas. Anlisis Multivariado. AquaChem,Egipto. Darb El-Arbaein.

1. Introduction

The groundwaier represents a resource for multiple uses(General Authority for Rehabilitation Projects and Agricul-tural Development, GARPAD, 1998-2001). They irrigate12000 feddans ( 1 feddan ~ 1.038 acres) and help 16 villagesfor farmers along about 400 km from Paris town towards theEgypt-Sudan border. The pumping wells are located in threeparts, the northern, the central, and the southern part of DarbEl- Arbaein (Fig. I). The northern part extends 90 km to thesouth from Paris town and has an area of 90 km-^ . The centralpart extends for 80 km to the south of the northern part andhas 120 km- in area. The southern part extends for 200 km tothe south of the central part and has 170 km- in area. TheDarb-El Arbaein is located in an arid region, where the abso-lute maximum- air temperature are 48.6 "C in May and mini-mum -2 ^ 'C in Febmary. The annual rainfall is less than i.lmm. the total monthly rainfall is 0.3 mm. The annual evapo-ration is about 172 mm. and the maximum evaporation ratein June is about 21.32 mm. The northern, middle, and south-

Rl-Dakhia

em Darb El Arbaein aquifer were treated statistically in or-der to clarify the impact of lithogenic and anthropogenic fac-tors. The saturation indices and partial pressure of CO2 wasestimated by AquaChem to delineate the change in pressurefrom the atmospheric to the current conditions. The statisti-cal analyses and AquaChem (PHREEQC) were used to delin-eate the impact of lithogenic and anthropogenic sources onaquifer system. AquaChem (PHREEQC version 2) is a com-puter program written in the C programming language that isdesigned to perform a wide variety of low-temperatureaqueous geochemical calculations.

/. / Geomorphology and geological setting

Darb El- Arbaein is subdivided into three gomorphologieunits, the southern Nakiai-Sheb peneplain; the westernAtmur peneplain; and a plateau surface (Issawi 1971).

Geologically, the exposed rocks range T>m Pre-Cam-brian to Quaternary sediments (CONOCO 1989). The

Figure I. Location map of Darb El Arbacin,

167

ABDEL-LATTIE. A. AND MOHAMED EL KASHOUTY

lithostratigraphic successions are divided into seven units,from base to top (CONOCO 1989, Fathy el al., 2001. Koranyet at.. 2002, Ghazal. 2002 and El-Gammal, 2004):

I) PreCambrian basement; 2) Paleozoic-Mesozoicsandstone; 3) Lower Cretaceous; 4) Upper Cretaceous; 5)Paleocene; 6) Eocene; and 7) Quaternary. The Nubian sand-stone is classified into Shab, Qusier, and Taref members(Issawi 1973). The Kisieba Formation is equivalent to bothShab and Qusier members and Taref is equivalent to Tarefmember (CONOCO 1989). The lithostratigraphic sequencein the northem, central, and southem part of DarbEl-Arbaein is shown in Table 1. The sedimentary cover in-creases far in the northem part (more than 100 m). while itincreases to the southem part of the northem Darb-ElArbaein. There is a little thickness variation in the southemDarb El Arbaein. The Dakhla shale represents the cappingaquifer only in the central Darb EI-Arbaein. The DarbEl-Arbaein area is related stmcturally to the Red Sea andsouthwestem regions (EGSMA 1987a and b). Issawi (1971)has identified the faults in E-W, NE-SW and NW-SE and

three anticlines (Bir Kiseiba, Rage, and Shirshir). Theuparching of basement rocks is encountered (Fathy et al.,2002).

1.2 Hydrogeological conditions92 wells were designed by GARPAD in the period from 1998to 2001, with depths from 130 to 535 m. They penetrated theNubian sandstone successions (Paleozoic-Upper Creta-ceous), which overlay Pre-Cambrian basement rocks. Thegeneralized hydrogeological section indicates that the area isdissected by 18 normally -exposed faults and concealedfaults (Fathy et ai. 2002). The central area bordered byGabal Abu Rayan El-Bahari from the north and the Kiseibaanticline from the south. The natural recharge of the aquifersystem in the Westem Desert is thought to be of about 1.5billion vc?ly (Ambroggi. 1966), while groundwater flowfrom Libya to Egypt is about 3.782 million mVy (Ezzat andAbu Atta, 1974). The groundwater believed to have accu-mulated and preserved in the Nubian sandstone aquifer since10000 y BC or even earlier as revealed by Cu and H3 iso-

Table 1. Lithostratigraphic sequence in the Darb El-Arbaein [CARPAD etal., 2001).

Upper Cretaceous

Paleozoic-Mesozoic Sandstone layer

Pre-Cambrian

Upper Cretaceous

Paleozoic- Mesozoic Sandstone layer

Pre-Cambrian

Upper Cretaceous

Pre-Cambrian

Location

1- Northern Darb El Arbaein

Campanian-Maestrichtian

Turonian-Santonian

Ash basement

2- Central Darb El Arbaein

Maestrichtian - EariyPaleocene

Campanian-Maestrichtian

Turonian-Santonian

Ash basement

3- Southern Darb El Arbaein

Campanian-Maestrichtian

Turonian-Santonian

Ash basement

Formation

Quseir

Taref

Dakhla

Kiseiba

Taref

Kiseiba

Taref

Max. thickness 'average, m

73-112

101 - 202

7 - 4 5

Base is not reached

161 -285

73-112

75-116

7 - 6 4

Base is not reached

44 - 150

56-80

Base is not reached

168

STATISTICAL INVESTIGATION OF THE GROUNDWATER SYSTEM IN DARB EL-ARBAEIN. SOUTHWESTERN DESERT. EGYPT

topes {German Water Group, 1977). The stored water inNubian sandstone is mainly fossilized water and ranges from20000 to 40000 y (Shata et ai. 1962 and Shata 1982).

built up of Qusier Fm., Taref Fm.. and Paleozoic-Mesozoicsandstone layer. The sediments gets up finest upward, theTaref Fm. is more permeable than the Qusier Fm.

1.2.1 Northern Darb El Arbaein

The aquifer is composed of sandstone of Qusier and TarefFormations and Paleozoic-Mesozoic sandstone layers. Theupper-most layer of Qusier Formation act as confining layer.The aquifer thickness increases to the northem part. Theaquifer is underlain by basement rocks. The latter is becomedeeper nortbward indicating tbe influence of concealedfaults (NW-SE) and the increase of sedimentary cover to thenorth (Fathy et ai, 2002). The groundwater flows to theeastem, northem. and northeastem part (Fig. 2a). The hy-draulic conductivity (Fig. 2b) and transmissivity (Fig. 2c)increases to the northem, northwestem, and southwestempart of the northem Darb El Arbaein. The well efficiencyranges from 61 to 71 % at discharge 150 m^/h. The northemDarb El Arbaein is dissected by normal faults (mostlyNW-SE). These faults increase the sedimentation to thenoiih and northeast. Tbe vertical displacement of formationsalong fault plane makes juxtaposition of permeable againstimpermeable layers. It influences aquifer thickness, precipi-tation/dissolution, and groundwaler salinity. Such displace-ment diminishes the hydrogeological characteristics of theaquifer system towards the south and south-east. Thehydrogeopbysical cross sections (A-A'), (B-B'), and (C-C)(Fig. 3) revealed that the boreholes fully penetrated theNubian sandstone successions (Paleozoic-Upper Creta-ceous). The latter overlie the Pre-Cambrian basement rocks(E! Gammal 2004). The Nubian sandstone succession is

1.2.2 Central Darb El Arbaein

The groundwater flows from the nortbem and northwestempart towards the southeastern part (Fig. 4a). Tbe Dakhiasbale thickness increases in tbe soutbem part (Fig. 4b) of thecentral Darb El Arbaein. Tbe hydraulic gradient has changedin the studied area, attributed to structural pattems andlithological changes. The water level dropped about 30 m(average) in 2005 compared in 2000, because of bigh pump-ing, increase in wells, and low recharge. The efective po-rosity of sand layers ranges from 21 to 30%. transmissivityranges from 280 to 540 m-/d, and storativity ranges from0.00011 to 0.0009. The aquifer facis (Nubia facis) are rep-resented by the Paleozoic- Mesozoic sandstone layers andUpper Cretaceous rock units (Taref and Kiseiba Forma-tions) (Fig. 5) (EI Sayed 2005). Tbe basement rocks form thebase of the aquifer, while the Dakhia Formation acts as im-permeable. The thickness ofthis aquifer ranges between 200and 230 m.

1.2.3 Southern Darb El Arbaein

Tbe aquifer is built of Kiseiba and Taref Fomiations of theUpper Cretaceous (Fathy et ai, 2001). The upper -mostlayer of Kiseiba Formation act as confming layer. Tbe aqui-fer thickness increase in tbe southem part, attributed to highconcentration of faults to the north. The aquifer is composedof coarse grained sandstone at the base that changes gradu-

2706000

2705000

2704000

2703000

2702000

2701000

2700000

2699000

2698000

2697000

^ '~ l ' if-^ ^ ' * "

lL_-'-y-^' ''

i-:-:-:-:'_v.;'\/'''5> J a- PiBzomotnc leyol. m '" GtDundwBlar (low - -~