Geochemical Modeling and Statistical Analysis for Groundwater Evolution Assessment in Wadi Qasab, Sohag, Eastern Desert, Egypt

Qasab basin is one of the most promising areas for the sustainable development in the Eastern Desert fringes of the Nile Valley, Egypt. The integration between statistical analysis, stable isotopes as well as geochemical modeling tools delineated the geochemical possesses affecting groundwater quality and detected the main recharge source in Qasab basin. The most of groundwater samples are brackish (88%), while the minority (12%) of the samples are fresh. The electrical conductivity of groundwater ranged from 1135 to 10,030 μS/cm. The statistical analysis and hydrochemical diagrams suggest that the groundwater quality is mainly controlled by several intermixed processes (rock weathering and agricultural activities). The mineralization of the Pleistocene groundwater is regulated by the rock weathering source, evaporation processes and reverse cation exchange. The isotopic signatures (δH and δO) represent two groundwater groups. The first group, is enriched with the isotopic signature of δO, which ranges from 0.9‰ to 5.5‰. This group is mostly affected by the recent meteoric recharge from the surface water leakage. The second group, is relatively depleted with the isotopic signature of δO, reflecting a palaeo recharge source of colder climate. The δO‰ varies from −10.1‰ to −6.4‰, indicating upward leakage of the Nubian sandstone aquifer through deep seated faults. The inverse geochemical model reflects that the salinity source of the groundwater samples is due to the leaching and dissolution processes of carbonate, sulphate and chloride minerals from the aquifer matrix. This study can demonstrate the hydrochemistry assessment guide to support sustainable development in Qasab basin to ensure that adequate groundwater management can play to reduce poverty and support socioeconomic development.


Introduction
Groundwater plays a significant function in the implementation of the sustainable development policies in the desert fringes in the Eastern Desert of Egypt. The over pumping of groundwater without regulator restrictions of the triggers causes the degradation of aquifers and the loss sustainable wise. It contributes to the restrictions in developing proposals in these areas. The depletion of water supplies and the groundwater quality degradation present persistent challenges to the sustainable development and make it necessary to conserve water security through all means. In the study area, the water demand for domestic and industrial sectors was sufficient for the agricultural land in the winter, while in the summer months the percentage of the available water only covers 57% from the daily needs (Omar & Moussa, 2016). It decreases by 27% of water usage by importing food and other indirect products (Gad, 2017). Recently, Sohag Governorate is trying to reclamate the desert fringes East the River Nile in Qasab basin. The main reclamation projects focus along the main channel of Qasab basin, where the farmers depend mainly on groundwater for irrigation; however the aquifer is ill-constraint and there are no sufficient hydrogeological and hydrochemical data about groundwater potentiality or quality. Therefore, the hydrogeological and the hydrogeochemical data about the concerned aquifer should be well investigated in order to provide accurate data for the decision makers for future infrastructure planning as well as consideration of the economic return for cultivating these lands.
The hydrochemical characteristics of the groundwater are used for tracking the groundwater circulation processes in order to identify the processes controlling the groundwater chemistry and geochemical processes affecting groundwater quality. Groundwater chemistry is influenced by the natural factors including the aquifer lithology, geological structure, recharge, geochemical reactions within the aquifer, and the rate of groundwater flow from recharge to discharge areas through its passage (Appelo & Postma, 2005), in addition the anthropogenic practices such as groundwater over pumping, unregulated drilling of wells as well as the unlimited agricultural and industrial activities (Huang et al., 2013). Understanding aquifer geochemistry and recognizing the causes of the depletion of groundwater are critical for controlling and enhancing the management of the groundwater resources (Trabelsi & Zouari, 2019).
The multivariate statistical analysis techniques are powerful in the investigations of groundwater chemistry. This technique helps to classify groundwater and delineate major mechanisms influencing groundwater chemistry (Cloutier et al., 2008). Geochemical modeling is commonly used for the investigation of water-rock interface. It aims to delineate the chemical reactions occurring along groundwater is important for providing information on the groundwater recharge source and salinization mechanism (Marković et al., 2020). The integration between hydrochemical interpretation diagrams, multivariate statistical analysis of groundwater chemistry and Inverse geochemical models as well as environmentally stable isotopes ( 18 O and 2 H) constitutes effective approach to assessment the geochemical process and the water quality criteria in the studied systems (Singh et al., 2017;Trabelsi & Zouari, 2019;Eissa et al., 2019).
The main objective of this study is to identify the hydrochemical characteristics, the processes controlling the groundwater quality and the groundwater origin as well as assessment of the main groundwater aquifers for irrigation purposes in Qasab basin in the Eastern Desert fringes of Sohag Governorate region, Egypt.

General Setting
Qasab basin is situated in the Eastern Desert south east of Sohag Governorate, Egypt between longitude 31.85˚E to 32.3˚E and 26.15˚N to 26.45˚N , covers about 2000 km 2 (Abdel Moneim, 2005). Qasab basin is bounded by the River Nile from the west and the Eastern Desert hilly from the east (Figure 1). The study region belongs to Egypt's arid zone, which is marked by long and hot summer, cold winter, low rainfall and high evaporation. The maximum temperature reaches to 36.9˚C in the summer and the minimum is 19.7˚C in the winter (Farrag et al., 2015). The mean annual rainfall over the Sohag governorate reaches about 1.2 mm, while the high rate of potential annual evaporation 2395 mm/year (Gomaa, 2006

Geomorphological, Geological and Hydrogeological Setting
Geomorphologically, Qasab basin is characterized by three main geomorphological units. The first unit is the Nile flood plain of the cultivated lands. Its altitudes range from 55 to 65 m above the sea level (masl). This unit consists mainly of clay and silt sediments. The second unit is the low desert land area of old alluvial plain which is amongst the Nile flood plain and the Eocene limestone plateau. Its altitude ranges from 70 to 140 m and gentle westward slope. The third unit is the Eocene limestone plateau. This unit occupies the eastern parts of the study area and forms the higher relief feature. Its altitude ranges from 200 to 375 m (Youssef et al., 2011).
Geologically the outcrops of the study area are ranging in ages from Eocene to Quaternary (Figure 2 (Gomaa, 2006) (Said, 1960); 2) Late Pliocene or Early Pleistocene is represented by Issawia formation. It composes of lacustrine deposits of carbonate and clastic facies (Issawi et al., 1978;Omer, 1996); and 3) The Quaternary deposits are presented the Pleistocene and the Holocene deposits. This formation is widely distributed on both the surface and subsurface along the Nile valley (Said, 1975(Said, , 1981. The subsurface units were identified via the Balyana-1well geological report located at the west to the study area ( Figure 2(b)). The subsurface units show that pre-Cambrian granite is followed by Taref formation. Taref formation consists of kaolinitic pebbly sandstone with shale and pink feldspar. This formation is overlain Qusayr formation.  (Ghazala et al., 2018). By the beginning of Pleistocene the local depressions were left receiving water only during rainy storms, and accumulated lacustrine sediments (Issawi et al., 1978). The Late Pleistocene (Dandara Formation) is represented by flood plain deposits. This deposits composed of fine silica clastic beds (siltstone, claystone, and fine-grained sandstones) and accumulated on the Nile River banks. The Holocene and recent sediments consist of cultivated lands were formed by silts and clays (Ahmed, 1980).
Hydrgeologically the Pleistocene alluvial aquifer represents the main aquifer in the Nile valley. It mainly composes of sands and gravels with clay lenses. It overlain by Holocene aquitard (Nile silt and clay) and underlain by marine Pliocene clay aquiclude of very low permeability (Gomaa, 2006) (Figure 2(c)). The aquifer thickness varies between 50 and 260 m (Gomaa, 2006). Generally, the aquifer thickness vanishes toward the limestone plateau and faulted against Eocene limestone from east to west (Figure 2(c)). The Pleistocene aquifer presents, semiconfined conditions in floodplain areas and unconfined conditions in the desert fringes due to the absent of the silt clay layer (Said et al., 2020). The average hydraulic conductivity is about 70 m/day (Attia et al., 1986). The aquifer is recharged by the seepage from the surface water and the excess irrigation water.
These waters seep vertically under the cultivated lands and flow horizontally toward the desert fringes (Gomaa, 2006). The groundwater flow in Qasab basin is towards the River Nile. The lowest groundwater table is close to the River Nile 53 m (masl) and the highest at the valley fringes 67 m (masl) (Ahmed & Ali, 2009). Accordingly, the River Nile acts as discharge system of the Pleistocene aquifer, as well as seepage into the agricultural drains and the irrigation canals during water restriction in the winter period (Said et al., 2020).

Water Sampling and Analytical Techniques
Sampling Procedure Thirty five water samples were collected from the study area during November 2018. Thirty three are groundwater samples represented the Pleistocene aquifer, one sample is from the irrigation canal (Eastern Nagaa Hamadi canal) and one sample is from the agricultural drain (Arab El-Sabah drain) ( Figure 1).  (Epstein & Maida, 1953) and 2 H (Coleman et al., 1982).

Data Analysis
The geographical and the groundwater quality distribution maps were carried out using Geographic Information System (GIS) software package Global mapper 11 and golden software surfer 12. Hydrochemical diagrams (Sulin, 1946;Piper, 1953;Gibbs, 1970) were performed using Aqua Chem V, 3.7.

Statistical Analysis
A multivariate statistical method was performed by using SPSS V.16 software.
The relations between groundwater chemistry variables were determined by Pearson correlation coefficient and Hierarchical cluster analysis (HCA). These effective tools can be used for identifying the hydrorgeochemical processes that  (Gat, 1981). The Global meteoric water line (GMWL) represents the present-day global precipitation according to this relation δ 2 H‰ = 8 δ 18 O‰ + 10 (Craig, 1961).

Inverse Geochemical Modelling
The saturation indices for the groundwater samples in the study area were computed using the inverse geochemical model NETPATH 2.0 (Plummer et al., 1994), according to the equation that was suggested by Lloyd and Heathcode (1985). When the saturation index (SI) value is negative, it indicates that groundwater is unsaturated with respect to that particular mineral. When SI index is positive, it indicates that the groundwater is being saturated with respect to the particular mineral phase (Langmuir, 1997).

Groundwater Evaluation for Irrigation Purposes
In this study; the groundwater samples were evaluated for the irrigation purposes on the basis of Irrigation Water Quality Index (IWQI) (Spandana et al., 2013). According to Ayers and Westcot (1985) and Rowe and Abd el-Magid (1995) the acceptable parameters of the irrigation water quality requirements were used. The American classification diagram (US Salinity Laboratory Staff, 1954) had developed a system for classifying the irrigation water quality relating to the graphical analysis.

Physicochemical Parameters, Major Ions Distribution and Trace Metal Contamination
The Pleistocene groundwater samples in the investigated area were neutral to slight alkaline with pH levels ranging from 7.1 to 8.2 (Table 1). These may be due to the dissolution of alkaline cations or bicarbonates from the mineralogical source or dissolved hydroxide the water resources. Electrical conductivity (EC) ranged from 1135 to 10,030 µS/cm with the mean value 3499 µS/cm (Table 1). water (1000 > TDS < 10,000 mg/l), while the minority (12%) of the samples are fresh water (TDS < 1000 mg/l) (Freeze & Cherry, 1979).  SO − increases towards the old cultivated lands due to gypsum dissolution as well as the agricultural activities (addition of sulphate fertilizers to the soils). Cl − concentration in the groundwater samples varies from 764.9 to 2450.9 mg/l ( Table 1). The concentration of Cl − increases in the study area as same as the increasing direction of Na + due to the dissolution of halite mineral (NaCl) (Figure 3).

Water Type and Groundwater Origin
The The relation between r Cl − − r (Na + + K + ) with Mg 2+ and r (Na + + K + ) − r Cl − with 2 4 SO − in meq% unit are plotted on Sulin diagram ( Figure 6). For the interpretation of the origin of the groundwater in the study area (marine or meteoric water), it is clear that the majority of the groundwater samples (76%) are located in old meteoric water area (Na 2 SO 4 ). The minority of the samples (24%) are located in recent marine water (MgCl 2 ). MgCl 2 reveals that the dissolution of the marine salts from the Eocene limestone plateau (Abdulhady et al., 2018).
This may indicate that mixing of the old meteoric and marine origin of the groundwater and/or the groundwater is mixed with the upward leakage from the deep aquifer (Abdel Moneim et al., 2015).
The groundwater samples in the study area are characterized by two assemblages of the combination salts:    The majority of samples (70%) are characterized by assemblage I (3 sulphate salts). They represent intermediate stages of the groundwater chemistry evolution, which reflects that the chemistry of this water is due to the leaching and dissolution of terrestrial salts during the surface and subsurface runoff. About 30% of groundwater samples characterized by assemblage II represent an advanced groundwater chemistry evolution. Presence of MgCl 2 and MgSO 4 reflects that these waters are influenced by the dissolution of the marine salts from the Eocene limestone plateau.

Mechanism Controlling Groundwater Chemistry
Water rock interaction, evaporation and precipitation processes are the main processes that can generate the solutes in the groundwater (Mackenzie & Garrells, 1965). A Gibbs plot (Gibbs, 1970) (Figure 7) reflects that there are two group of groundwater samples. The firist group is consists of the majority of the groundwater samples (82%). This group is coincided with the evaporation dominance, indicating the influence of the evaporation processes on the groundwater chemistry during the surface runoff before the aquifer recharge. The second group (18% of the groundwater samples) is located in the rock dominance end member zone reflect rock weathering source.
The hydrochemical relations are used for identifying the influence of evaporate dissolution, silicate or carbonate weathering on the groundwater chemistry ( Figure 8). The relation between Ca/Na vs Mg/Na (meq/l) shows that most of the Mg 2+ is derived from weathering of the silicate minerals with the influence of the evaporation processes (Figure 8(a)). The relation between TDS vs Ca 2+ /Mg 2+ shows that the groundwater samples, which have TDS values lower than 1600 mg/l, have Ca 2+ /Mg 2+ values > 1. It indicates that the dissolution of calcite is the main controlling factor. The dissolution of dolomite is the main controlling factor where the groundwater samples of TDS more than 1600 mg/l have Ca/Mg < 1 (Figure 8(b)). The scatter plot between Cl − vs Ca 2+ + Mg 2+ (Figure 8(c)) shows  that most of the groundwater samples located below the aquiline indicates the dominance of reverse ion exchange. The relation between Na + and Cl − ( Figure  8(d)) shows that the majority of the groundwater samples (76%) located above the aquiline reflected that the dominance of sodium from the silicate weathering. That may be attributed to the leaching and dissolution of terrestrial salts. The minority of the groundwater samples (24%) have rNa + /rCl − < 1. This is may be due to the leaching and dissolution of the marine deposits that may be transported by weathering. This weathering is from the Eocene limestone plateau beside the contribution of cation exchange processes between Na + and (Ca 2+ & Mg 2+ ).
The Chloro-Alkaline Indices (CAI) helps to identify the chemical composition changes in the study area. According to the calculation of CAI 1 and 2 which are suggested by Schoeller (1977), the majority of the computed average values of the CAI 1 and 2 for the groundwater samples (70%) are negative values. They reflect the exchange of Ca 2+ and Mg 2+ from water with Na + and K + from rocks (Reverse cation exchange), where 30% of samples are positive values. They reflect the exchange of Na + and K + from water with Ca 2+ and Mg 2+ from rocks. This is may be due to presence of clay minerals (Figure 9). The hydrochemical profile attempt ( Figure 10) is made to identify the spatial variation of the groundwater chemical composition throw its flow path, in the direction from the Northeast to the Southwest from the upstream to the downstream of Wadi Qasab. There are considerable variations in the chemical composition of the groundwater. Due to variations in water occurrence, rock properties and recharge source as follows; the hydrochemical profile pass through 10 wells along the concerned aquifer in Wadi Qasab. The profile shows that approximate stability in the chemical composition from the upstream to the downstream before the rapid increase in the TDS and chemical composition in the   well (No.,17). This may be due to the Pliocene clay mineral. The high decrease of the TDS value and the chemical composition in the end of the profile (well No., 15) is due to the influence of the fresh water recharge from the surface water seepage. It reflects the decrease of the concentration of chloride and sulphate salts and the increase of the Ca(HCO 3 ) 2 salt.

Coefficient Correlation (R)
Correlation analysis is one of the statistical tools used for indicating which E. Zaghlool ions control the water salinization (Zeng & Rasmussen, 2005). In the study area strong correlations (>0.7) have been observed between EC and TDS with Ca 2+ , Mg 2+ , Na + , 2 4 SO − and Cl − . This indicates that EC, TDS are controlled by these ions (Table 3). The ion exchange of the primary salts and the leaching or dissolution processes of the secondary salts are the main processes that controlling the Pleistocene groundwater salinization. These are due to the geological formations in the study area. A high positive correlation between Na + and Cl − suggests that mixing of groundwater with two different compositions (fresh and saline) and a strong relationship with 2 4 SO − and Cl − may be due to the influence of the evaporation processes (Kumar et al., 2014). The strong correlation between Ca 2+ and 2 4 SO − suggests the dissolution processes of gypsum mineral.

Cluster Analysis
The results of Q-mode of HCA for the groundwater samples depend on the position of the cases on the Dendrogram (Figure 11). It shows 2 major clusters (cluster 1 and cluster 2) and 2 subdivisions of cluster 1 (cluster 1 a and cluster 1 b ). The groundwater samples which belongs to cluster 1 reflect the TDS values less than 5000 mg/l (94% of groundwater samples) reflect the same sources of the groundwater chemistry. Cluster 1 is divided in to two sub clusters. Sub cluster 1a reflects samples with TDS values less than 3000 mg/l (76% of groundwater samples). These samples located closed to the watershed area or influenced by recharge from freshwater resources. Sub cluster 1b which has TDS values ranges from 3000 to 5000 mg/l (18% of groundwater samples). These samples located in the downstream of Qasab basin reflect that the relative increase in TDS values is due to the leaching and dissolution of terrestrial salts through groundwater flow path. Cluster 2 is characterized by high salinity groundwater TDS values > 5000 (6% of groundwater samples). These samples are located in the downstream of Qasab basin closed to the Eocene limestone plateau reflect the effect of the old marine deposits.   R-mode cluster reflects two main cluster. They reflect the interaction between variables (cluster 1 and cluster 2). Cluster 1 is divided in to two sub clusters (cluster 1a and cluster 1b). Sub cluster 1a reflects the correlation between pH, Ca 2+ , Mg 2+ , K + , 2 3 CO − and 3 HCO − ions. This may indicate that the salinization may be due to dissolution of carbonate salts (aragonite, calcite and dolomite), where Sub-cluster 1b reflects good correlation between Na + , Cl − and 2 4 SO − . This correlation may indicate that the source of the groundwater salinization in Qasab basin is due to the leaching and dissolution of chloride salts (halite) and sulphate salts (gypsum). Cluster 2 shows the correlation between EC and TDS.

Stable Isotopes
The stable isotopes content in the groundwater provides good insights about the main recharge and salinization sources (Eissa et al., 2013). According to the stable isotopes (δ 2 H‰ and δ 18 O‰) values for the water resources in Qasab basin (Table 4 and Figure 12), two groundwater clusters can be identified in the δ 2 H‰ vs δ 18 O‰ plot (Figure 12(a)) reflects different groundwater origin and recharge sources: Recent alluvium aquifer (group A): The groundwater samples of this group are enriched with the isotopic signature of δ 18 O and δ 2 H. This group has positive δ 18 O‰ values which range from 0.9 to 5.5 and δ 2 H‰ from 17.2 to 54. The groundwater samples are plotted more close to the isotopic signature representing surface water (irrigation canal water, agricultural drainage water and the old Nile before Aswan High Dam construction (Awad et al., 1994)). These varied values reflected the recent recharge (last decade) from the surface water leakage (irrigation canal water, agricultural drainage) and the River Nile floods before Aswan High Dam construction. The scatter plot for Group A gives the regression line of equation δ 2 H‰ = 8.93 δ 18 O‰ + 2.86. The deviation from the Global Meteoric Water Line (GMWL) (Craig, 1961) reflects the evaporation influence occurred before the recharge processes.   (Craig, 1961) that the groundwater samples influenced by evaporation processes. This group is plotted closer to the isotopic signature of the Nubian sandstone groundwater in Wadi Laqita δ 2 H‰ = −68.2, δ 18 O‰ = −9.7 (Sherif et al., 2019) located Southern Qasab basin. These negative values were derived from a paleo-precipitation that occurred many thousands of years ago during the pluvial time (Ahmed, 2008). This confirms that, this group is charged from the upward leakages from the Nubian sandstone aquifer through deep seated faults (Figure 2). The upward leakage of groundwater phenomena has been reported in Wadi Qena basin (Hussien et al., 2016), and Wadi El-Assyuti located in the southern and Northern of Qasab basin; respectively (Sultan et al., 2007).
The relation between Chloride vs δ 18 O‰ for the groundwater samples in the study area (Figure 12(b)) indicates that the salinization source of both of the two groups is due to the leaching process. Throughout the runoff and dissolution process inside the aquifer with influence of evaporation prior to the recharge process occurs.

Inverse Geochemical Modeling
In order to delineate the origin of the groundwater mineralization, saturation indices (Aragonite, Calcite, Dolomite, Gypsum, and Halite), the results of saturation indices reflects positive values with regard to aragonite, calcite and dolomite for the majority of the groundwater samples (Table 5). This reflected the geological origin from the carbonate weathering. These samples suggested the saturation of these minerals. The relation between EC (µS/cm) and SI values in ( Figure 13) for the groundwater samples reflects that the EC values are not Figure 13. The relation between the SI of minerals in the Pleistocene ground water samples and the electrical conductivity (EC) μs/cm.  SO − , Cl − were introduced into the model as constrains. The results of the Netpath software for the mass balance transfer along the flow path reflect the evolution of the groundwater along its flow path direction from the upstream to the downstream of Wadi Qasab. Two models were assumed in this study, the first model is for palaeo water and the second is for the samples that are originated from the runoff before Aswan High Dam construction with some influences from the irrigation canal and agricultural drainage. The reaction models are accepted according to the comparison of the evaporation factor that is estimated from Net path model and the fraction evaporation loss (F E ) that is estimated from isotope the mas balance equation (Gonfiantini, 1986) (Table 5). The first model assumes that the initial water is the Pleistocene water (

Groundwater Assessment for Irrigation Purposes
The irrigation water quality index (IWQI) for the groundwater samples is calculated (Table 6) in order to evaluate the groundwater for irrigation purposes. IWQI  (Richards, 1954). This diagram developed a procedure for irrigation water classification, relating on a graphic analysis basis, where EC is plotted against SAR. The USSL diagram shows that 6% of the groundwater samples are located in C 3 -S 1 ( Table 6 & Figure 14). These samples indicate low alkalinity with high salinity of water. They reflect that this water can be used for irrigation in all types of soils with little danger of exchangeable sodium. 24% of samples are located in C 3 -S 2 and C 4 -S 2 fields reflecting medium sodality and high salinity. This type of water cannot be used in fine grained soils where the drainage is restricted due to the accumulation of salts in the root zones of crops. This leads to salinity and soil clogging crisis. This type of water is satisfactory only for irrigation of plants with good tolerance. It may be used in coarse-textured types of soils or organic types of soils with good permeability. 15% of samples fallen in C 3 -S 3 class show high salinity water and high sodium water. They reflect that this type of water is satisfactory only for irrigation of plants with good tolerance with the adequate drainage system. 30% of samples are located in C 4 -S 3 and C 4 -S 4 fields class reflect very high salinity water and very high sodium water. They are suitable only for irrigation of very salt-tolerant crops due to the high SAR values under very Figure 14. Classification of water samples for irrigation uses, with respect to EC and SAR, USSL diagram.

Conclusion
The main objective of this study is to identify the hydrochemical characteristics, the processes controlling the groundwater quality and the groundwater origin as well as assessment of the main groundwater aquifers for irrigation purposes in Qasab basin in the Eastern Desert fringes of Sohag Governorate region. The integration between statistical analysis, environmental stable isotopes, and invers geochemical modeling suggest variations in the groundwater aquifer's hydrochemical characteristics as well as the different background of recharge origin.
Hydrochemical results demonstrate that the majority of samples are brackish water. The salinity of the groundwater increase towards the south-west direction is influenced by the interaction of groundwater and the geological materials as well as the contribution of the seepage from the surface water systems (Irrigation canal & agricultural drain). Groundwater mineralization is controlled by the evaporation processes during the surface runoff before the aquifer recharge, and few samples are influenced by rock weathering source. The wide variation of Fe concentration suggests that its content is controlled by several intermixed processes. and Pb may be attributed to the agricultural activities, which reflects another source of groundwater contamination with respect to Fe. The statistical analysis indicates that the ion exchange of the primary salts and the leaching or dissolution processes of the secondary salts as well as the anthropogenic activities are the main processes controlling the salinization of the Pleistocene groundwater. R-mode cluster reflects the interaction between variables; this may indicate that the salinization may be due to dissolution of carbonate salts (aragonite, calcite and dolomite), beside the leaching and dissolution of chloride salts (halite) and sulphate salts (gypsum).
The isotopic signature ( 2 H and 18 O) for the water resources represents two forms of groundwater; the first of them is the groundwater wells located in the downstream of Wadi Qasab affected by the recent surface water leakage (irrigation canal water, agricultural drainage). The second is palaeowater tapping because the Pleistocene aquifer is recharged from the upward leakages from the Nubian sandstone aquifer through deep seated faults. The inverse geochemical model (NETPATH) assumes two models. The first model assumes that both of the initial and the final water are Pleistocene water. This model reflects the dissolution of aragonite, dolomite, gypsum and halite. The second model assumes that the initial water is the Nile water and the final water is Pleistocene water. The model result reflects the dissolution of dolomite, gypsum and halite. These models reflect that the salinity source of the groundwater samples is due to the leaching and dissolution processes of carbonate, sulphate and chloride salts during the runoff processes and water rock interaction inside the aquifer.
The evaluation of water resources for irrigation purposes reflects that the groundwater samples are suitable for irrigation of good and high salt tolerance plants. The Pleistocene groundwater samples are suitable for irrigation of plants range from good to high salt tolerance plants. 6% of the groundwater samples can be used for irrigation in all types of soils with little danger of exchangeable sodium. 24% of samples cannot be used in fine grained soils and satisfactory only for irrigation of plants with good tolerance. 15% of groundwater samples are satisfactory only for irrigation of plants with good tolerance with the adequate drainage system. 30% of the groundwater samples are suitable only for irrigation of very salt-tolerant crops. 25% of the groundwater samples are only suitable for very salt tolerant crops with bad influence on the plant productivity. All the Pleistocene groundwater samples and the surface water samples are safe for irrigation purposes for long-term use in respect Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. 27% of the Pleistocene groundwater samples and the agricultural drainage sample are unsuitable for long-term irrigation purposes in respect to Cr concentration. 9% of the Pleistocene groundwater samples are unsuitable for long-term irrigation purposes in respect to Fe concentration. 6% of the Pleistocene groundwater samples are unsuitable for long-term irrigation purposes in respect to Mn concentration.
Based on the finding results of this research, drilling groundwater wells tap-ping the Nubian sandstone aquifer should provide additional sustainable groundwater resources for the study area. The subsurface lithology and groundwater exploration should be carried out through geophysical investigation and pore hole test well in order to provide clear image about the situation of such deep aquifer.

Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.