Integrated geostatistics and GIS techniques for assessing groundwater contamination in Al Arish area, Sinai, Egypt Mohamed El Alfy* and Broder Merkel** * Geology Department, Mansoura University, 35516 Mansoura, Egypt. [email protected] ** Institute of Hydrogeology, Gustav Zeuner Str. 12, D-09596 Freiberg, Germany. [email protected] Abstract The sustainable development in El Arish area (North Sinai, Egypt) is retarded by serious environmental problems, where the land use and land cover of the region is changing over time. The fast growth of the human activities in the study area is accompanied by the destruction and over-exploitation of the nature. The present study applies the multivariate statistics (factor and cluster analyses) and GIS techniques for the identification of anthropogenic and natural processes affecting groundwater quality of the Quaternary aquifer. The aim of this study was to investigate the impacts on groundwater resources, the potential pollution sources and to identify the main anthropogenic inputs affecting heavy metal contents. Since the depth to the water table is shallow and the aquifer has poor buffering capacity, the pollution risk is very high. Groundwater chemistry in this coastal region has complex contaminant sources, where, intensive farming activities and untreated wastes put stress on groundwater quality. Nemours areal distribution maps were constructed for correlating water quality with possible contributing factors such as location, land use and aquifer depth. These maps identified both anthropogenic and natural processes affecting groundwater quality of the studied aquifer. Cluster analysis was used to classify water chemistry and determine the hydrochemical groups, Q-mode dendrogram is interpreted and there are three main clusters. Factor analyses identify the contamination sources affecting groundwater hydrochemistry such as: nitrate, sulphate, phosphate and potassium fertilizers, pesticides, sewage ponds wastes, salinization due to circulation of dissolved salts in the irrigation water itself. Keywords: Groundwater contamination, Heavy metal, Geostatistics, GIS, Sinai, Egypt. Introduction A sustainable development is necessary to transform the fast and overheated growth into a long and steady development suited for the economy. Giving the planning authorities guidelines is an important milestone on the way to a sustainable planning. The area of study (93.5 km2) is located at Al Arish area, North Sinai, Egypt (Fig.1). The area locates within 31°01`29" and 31°09`02" longitudes 33°45`11" and 33°51`58" latitudes respectively. The study are located in the semi arid belt, where annual rain fall value is less than 100 mm/y and the evaporation value is > 1641 mm/y. This area is characterized by its shallow Quaternary aquifer, which is highly vulnerable for pollution. The aquifer is recharged mainly by rainfall with minor recharges from underlying aquifers. Intensive agricultural practices in the delta of wadi Al Arish combined with rain fall and good drained soils, make the unconfined Quaternary aquifer susceptible to nitrate contamination. The objective is to provide baseline groundwater quality data throughout the area and to address the potential pollution sources. Where maps containing simplified categories were carried out to evaluate the groundwater pollution. Plan was established that placed greater emphasis on determining trends in groundwater quality and correlating water quality with possible contributing factors such as location, land use and aquifer depth. All the constructed maps and their data-base were carried out using the Geographic Information System technique (TNTmips , GIS software), (Microimages, 2004). The maps were constructed using the integrated geomorphologic and hydrogeologic and land use aspects of the study area. In this regard, a total of 21 groundwater samples were collected at April, 2002, and investigated for major, minor and trace elements (Table 1). Materials and methods 256 to 270 Hydrogeologic setting Shata (1959), Salem (1963), Taha (1968) and Morsy et. al. (1995) studied the geologic units within the study area. The Holocene sand sheets, sand dunes, alluvial and beach deposits cover the study area surface. The sand sheets moves freely especially during storm periods. The modern sand dunes in the coastal belt form movable elongated ridges. While the stabilized sand dunes ridges are dominated in the southern part of the study area. Beach deposits are made up of loose sand and calcareous sandstone rich in shell fragments. The modern alluvial deposits are composed of sand, silt and loam. Pleistocene deposits are classified into three main units: old alluvial deposits, old beach deposits and Kurkar deposits (Figs. 2a and b). Old alluvial deposits are composed of three series; the upper one is composed of medium to coarse sands intercalated with silt; the middle one is composed of alternation of sand and calcareous clay, while the lower one is composed of alternating gravel and coarse sands interbedded with calcareous clay. Old beach deposits are composed of well sorted sands and sandstone intercalated with clay. Kurkar deposit is represented by calcareous sandstone; it is divided into two series, upper continental Kurkar and lower marine Kurkar (Figs. 2a and b). The Quaternary aquifer within the study area is characterized by intensive exploitation as well as by a great variety of natural factors affecting groundwater chemistry. This aquifer includes different geologic units (sand, sandstone and calcareous sandstone), which are thought to be connected according to their hydrogeological situation (Figs. 1 and 2). The principal source of recharge is percolation of groundwater through permeable soil and sands, also the aquifer is connected to the underline aquifers (Cretaceous aquifers) as a result of expected faults south of Al Arish (Dames and Moore, 1984). Since the mid of the last century, the continuous over pumping exploited the aquifer, where water table decrease dramatically with time. According to several hydrogeologic studies (Paver and Jordan, 1956, Geofizika, 1963, Dames and Moore, 1984, El Bihery and Lachmar, 1994, El Alfy and Merkel, 2006), groundwater table measurements indicate that there are noticeable rising during the winter (recharge season) and slight lowering during summer (the dry season). Groundwater flow is affected by rainfall recharge, excessive pumping, evapotranspiration and the hydraulic connection with the deeper aquifers. El Alfy and Merkel, 2006 carried out a water table contour map for the Quaternary aquifer in May, 2002, there was a general trend of flow from south to north, and this direction is dissected by numerous local flow directions towards the water depressions. Extensive agricultural activities within the area had resulted in several depression cones, which are represented by three main cones. The largest one is the located in the southern part with a diameter of approximately 50 km (El Alfy and Merkel, 2006). Fig. 3 shows the depth to water in the northern part is < 10 m, while it increases south word to > 70 m. This reflects the high vulnerability of the Quaternary aquifer in the northern part more than the southern part. Land use pattern and urbanization Different types of land uses are recognized within the study area, the northern part is represented by Al Arish city (urban build-up and rural areas), while the central and southern parts are prevailed by agricultural development. The main pollution sources concerning cultivated land is the excessive application of fertilizers and pesticides as well as unsewered rural and urban lands of long-term influence, while pollution sources connected with agriculture are mainly livestock farms. Groundwater sampling and analysis Ground-water-quality samples were collected from wells completed in the Quaternary aquifer, for this study, 21 wells (currently in use) were selected based on the preliminary field survey (Fig. 1). The selected wells are distributed over the study site and are used for domestic and agricultural purposes. Groundwater samplings were carried out in April 2002, where water samples were collected after stag- nant water had been pumped from the well casing. Electrical conductivity (EC), Oxidation-reduction (Eh), pH and temperature were measured directly in the field. Samples for laboratory analysis were immediately filtered in the field through 200µm cellulose membranes. Groundwater sampled to determine 2 the major components (Na, K, Ca, Mg, Cl, NO3, SO4 and HCO3) in 500-ml polyethylene bottles after three times of washing with the sample water. Collected samples for trace elements were acidified with several drops of ultra-pure hydrochloric acid. Different determination methods were used for the different elements such as titrimetric (HCO3 and CO3), Ion-Chromatography (IC, Combination Merck/Hitachi, D6000A) for Na, K, Ca, Mg, Cl, SO4 and NO3, inductively coupled plasma mass spectrometer (ICP-MS) for heavy metals and rare earth elements) and Spectophotometric (HACH Spectrophotometer DR/2000 for PO4), (Table 1). Results and Discussion Nitrite (NO3) and organic species are meta-stable compounds in aerated water, while ammonium is strongly sorbed on mineral surfaces. The Quaternary aquifer supports extensive irrigation activity and is subjected to contamination by nitrate. Nitrate concentration values range is 2–500 mg/l and the average value is 107 mg/l (Table 1). The small concentration value (2 mg/l) represents a background concentration. According