Study of Groundwater in Northeast Cairo Area, Egypt

This paper presents a comprehensive hydrogeologic view of the Quaternary aquifer in north eastern Cairo area, Egypt. The hydrogeologic, hydrochemical and isotopic features of the aquifer are determined to assess the groundwater geochemistry and quality for different uses. The groundwater in the aquifer is shallow and flows towards the heavily pumping areas (cultivated and industrial areas). The concentrations of total dissolved solids (TDS) vary considerably in the aquifer, ranging from 225.6 mg/L to 1219 mg/L. Wide variations in the concentrations of major ions, trace elements, nitrate, δO and δH are detected, indicating the variation in the geologic and recharge conditions. This further indicates the effect of natural processes (weathering, dissolution and ion exchange) as well as anthropogenic activities on the quality of groundwater. Moderate levels of contamination with nitrate, aluminum and manganese are recorded in the groundwater below the cultivated area. The contamination is linked to the extensive use of fertilizers for agriculture and the leakage of wastewater from improper sewage system. The computed nitrate pollution index reveals that about 69.69% of groundwater is safe for drinking, while the rest of groundwater is unsuitable. The calculated water quality index indicates that about 78.79% of groundwater is safe for human consumption and the rest of groundwater is poor for consumption because of the contamination with the high levels of manganese, total hardness, pH, sulphate, aluminum, and nitrate. The contaminated groundwater needs to be treated before consumption. Hence, periodic groundwater quality checks are recommended.


Introduction
In recent years, the demand for groundwater has risen to the highest levels in Cooperative Society Company (COOP) and Cairo Oil Refining Company (CORC) [11] [12]. Currently, a major refinery expansion project (the Egyptian Re-fining Company, ERC) is underway. The project includes several new units and aims at upgrading the range of petroleum products [4]. The area located southwest of the industrial zone is currently used, without authorization, as waste dump for the household wastes and building materials.

General Geology and Water Bearing Formations
As part of the eastern Nile Delta, the study area is dominated by the Quaternary sediments consisting of Nile silts, sand dunes and sands and gravel. To the east of the area, the oldest Tertiary rocks (Pliocene, Miocene, Oligocene, and Eocene sediments) appear on the surface. A brief description of surface geologic formations is associated to Figure 2. Table 1 shows the subsurface stratigraphic succession in the area and its vicinities. All rock units, but the Pliocene one, are considered water bearing formations [12] [13]. The Quaternary aquifer that is concerned by the present work has saturated thickness ranging from about 100 m in the study area to about 800 m near Mediterranean Sea [14] [15]. The major part of the groundwater is under semi-confining conditions. The Miocene, Oligocene and Eocene aquifers are of low significance because of their low quality waters.
The sedimentary rocks belonging to Cretaceous, Jurassic, Triassic and Carboniferous periods have not been examined as water bearing formations in the whole area.
Tectonically, the eastern part of Nile Delta, comprising the study area, falls within the unstable shelf that dominates north Egypt [20]. It shows a very complicated structural pattern represented by large number of faults, folds (anticlines and synclines) and basaltic extrusion [19]. The faults are the prominent   structural features in the area. They follow three main regional trends, the NE-SW (Syrian Arc folding system), NW-SE (Suez Rift trend) and E-W (Mediterranean trend) directions [21]. Faults play an important role regarding the distribution of geologic formations and groundwater flow in the desert area. The faults rendered the Miocene deposits to face the Quaternary and Oligocene ones [22]. The Quaternary aquifer is hydraulically connected with the Miocene and Oligocene aquifers through fault planes [18]. Figure 3

is a hydrogeologic cross
showing the hydraulic connection between these aquifers where one potentiometric surface is found to be common to all aquifers.

Methodology
An inventory of wells tapping the Quaternary aquifer, water level measurements, and sampling (water and aquifer materials) were taken from the study area in November 2015. Specification of the wells included the well heads, depths and diameters as well as screen and casing intervals. Depths to water inside these wells were measured and the coordinates and altitudes of wells were determined.
Thirty three groundwater samples from the aquifer and one surface water sample from Ismailia Canal were collected for major ions, nutrients, trace elements Figure 3. Hydrogeologic cross section in the area located to the northeast of the study area, showing the hydraulic connection between the Quaternary and Miocene aquifers, East Nile Delta area, slightly modified after [18]. and stable isotopes (oxygen-8 and deuterium) analyses. All the wells were in use at the time of sampling. The discharge rates of these wells were slow to prevent or minimize degassing till the physical parameters of water (pH, specific conductance and total dissolved solids) stabilized. Then, the physical parameters were measured in-situ using Manta 2, Water-Quality Multiprobe device, Model Sub 3, USA. All the water samples were collected into light polyethylene bottles that had been rinsed with water from the wells. The water sample from the Ismailia Canal was filtered using 0.45 µm pore-sized paper. For trace element analysis, all samples were acidified to pH < 2 with 20% nitric acid in order to prevent precipitation.
The water samples were processed and chemically analyzed following [26] where: R sample is the ratio of 18 [29], 2) the nitrate pollution index (NPI), and 3) the water quality index (WQI).
The NPI was calculated for all samples from the relation described in [30]: where Cs is the measured concentration in the sample and HAV is the threshold value of anthropogenic source (human affected value) taken as 20 mg/L. The quality of water was classified into three types based on the values of NPI: clean (unpolluted), light pollution, moderate pollution, with the NPI value: <0, 0 -1, 1 -2, respectively.
The WQI was calculated using stepwise methods as described in [31] [32]: where q i is the quality rating based on the concentration of i th parameter, C i is the concentration of each chemical parameter in each water sample in mg/L, Si For domestic uses, the assessment of the groundwater quality was based on its content of water quality index (WQI), which was calculated using the same stepwise methods described above. Here 13 chemical parameters were used to compute the WQI, they included the pH, TDS, TH, Na, Ca, Mg, Cl, SO 4 , Fe, Mn, Cu, Zn, and Al. The Egyptian domestic water standard [28] [29] for each chemical parameter was used to calculate the quality rating. The quality of water for domestic uses was classified into three categories based on the WQI values: excellent, good, and poor with the WQI value: <50, 50 -100, 101 -200, respectively [32].
For irrigation use, the quality assessment was based on the water quality index (WQI), which was computed using the stepwise method described above. Here 13 chemical parameters including SAR, EC, TH, pH, Na, Ca, Mg, K, Cl, SO 4 , HCO 3 , NO 3 and PO 4 were used to compute the WQI. The FAO irrigation standard [33] for each parameter was applied to calculate the quality rating. The quality of water for irrigation use was classified into three classes based on the WQI values: Class I (non restriction), Class II (slight restriction), and class III (moderate restriction) and with the WQI value: <150, 150 -300, 300 -450, and >450, respectively, [32].

Hydrogeologic Signature
The Quaternary aquifer in the study area is penetrated by a great number of private shallow wells. Most of these wells are found in the urban area, and their water is generally used for drinking and domestic uses. A few wells (Nos. 2, 7, and 9) are found in the agricultural lands around the industrial zone, and their water is used mainly for irrigation. All wells were drilled using hand-dug method.
Depths of these wells range from 12 m to 55 m, and their diameters range from 2 inches to 6 inches. The screen lengths range from 2.5 m to 20 m followed by sand traps. The casing and screen of wells are made of galvanized steel. These wells represent the main source of geologic, hydrogeologic and hydrochemical data used to conduct this study. The lithologic data are used to construct the hydrogeologic cross sections (Figure 4(a), Figure 4(b)) and the water level measurements are used to construct the depth to water and potentiometric surface contour maps ( Figure 5).

Hydrochemical Signature
A complete tabulation of the analytical data including physico-chemical parameters, major ions, nutrients and trace elements of groundwater samples taken from the Quaternary aquifer and Ismailia Canal are shown in Table 2 and Table   3. The groundwater has slight alkaline to alkaline nature. The electrical conductivity (EC) values indicate a very weakly to weakly mineralized water according to [34]. Concentrations of total dissolved solids (TDS) are variable and indicate a good potable to fairly fresh water according to [35]. The Nile water in Ismailia Canal is alkaline, dilute and has the lowest E C and TDS values (   The change in the concentrations of salinity (as TDS) and major ions is illustrated in Figure 6(a), Figure 6(b). The high increase in the salinity of groundwater is associated with the higher content of Cl − , 2 4 SO − , Na + , Ca 2+ , and Mg 2+ ions. The higher concentrations of such constituents are recorded for the wells 2, 7, 20, 21, and 22 drilled in and around the cultivated lands.
The nitrate content in groundwater varies considerably ( Table 2). An overabundance amount of nitrate content that exceed the maximum contaminant levels of 10 mg/L for nitrate [36] is recorded in 45% of wells. The higher concen- Low concentrations of phosphate ions are detected in the groundwater, ranging from a fraction of mg/L to o.72 mg/L, which is less than the maximum contaminant level of 1.0 mg/L for phosphate [37]. The concentrations of nutrients in Ismailia Canal water are generally low attaining 6.24 mg/L for nitrate and 0.02 mg/L for phosphate ( Table 2).
Contents of Cd, Co and Pb elements in groundwater of the aquifer are less than the detection limits of the used instruments for analyses ( Table 3)

Aquifer Geometry and Groundwater Movement
In the study area, the Quaternary aquifer is formed of heterogeneous materials of yellowish brown, medium to coarse-grained sands with occasional soft and brown clay lenses and few amounts of gravels and calcareous materials ( Figure   4(a), Figure 4(b)). The Quaternary aquifer is overlain by a semi-permeable Nile silty layer (aquitard) of Holocene age, rendering the aquifer under semi-confining conditions. The Nile silt layer is composed of heterogeneous and anisotropic materials (silt, clay and sand). It has a thickness that ranges from 15 m adjacent to Ismailia Canal due east to 5 m in the western part of the study area. The average hydraulic conductivity of the Nile silt layer ranges from 0.005 to 0.05 m/day [6]. The depth of water below the land surface is shallow, ranging from 2.5 m near Ismailia Canal due west and 4.3 m at Al Marg area due east ( Figure 5(a)).
The distribution of hydraulic heads in the aquifer is shown in Figure 5 which has originated from the heavy pumping of water to meet agricultural demands. Big separation between contour lines in the western part of the area implies more permeable aquifer materials, and the vice versa in the eastern part of the area. Most probably, the irregularity of contour lines is originated due the heterogeneity in the aquifer materials and the change in aquifer hydraulic conductivity. The aquifer hydraulic conductivity ranges from 62 m/day to 100 m/day [7].
Based on the directions of flow lines ( Figure 5(b)), the aquifer receives recharge from east and northeast directions (i.e. from Ismailia Canal), from the southern direction (i.e. from the Nile aquifer system) and from the west direction (most probably from the Miocene aquifer).

Hydrogeochemical Signature
The hydrochemical parameters and ionic ratios are used to throw light on some first group (group A) is represented by the majority of water samples having low salinity, ranging from 225 mg/L and 610 mg/L. The second one (group B) is represented by the groundwater samples 2,4,7,16,17,18,19,20,21, and 22 having a relatively high salinity between 630 mg/L and 1220 mg/L. The chemistry of low saline groundwater (group A) seems to be controlled by the natural geochemical factors such as silicates weathering and dissolution of halite, calcite, dolomite and gypsum minerals. Such processes increase the contents of Na + , Ca 2+ , Mg 2+ , 2 4 SO − and K + ions in the groundwater, meanwhile the increase in Cl − ion is insignificant. On the other hand, the chemistry of the high saline groundwater (group B) is primarily controlled by evaporation, where the chloride content increases without a significant increase in the related ionic ratios. This may refer to the contribution to the Quaternary aquifer from the evaporated surface effluents, especially in the cultivated and industrial areas.
The plot of 3 NO − versus Cl − ions (Figure 8(a)) indicates that the concentration of 3 NO − ions increase linearly by increasing the Cl − ions with correlation coefficient (R = 0.88). Similar trends are observed from the plots of Mn, Mo and Zn elements against Cl − ions where the concentrations of these elements increase as the Cl − ions increase (0.59 < R < 0.69) (Figures 8(b)-(d)). The high nitrate, chloride, manganese, molybdenum and zink contents in groundwater belonging to group B water are most probably due to contamination of recharge to the aquifer by deteriorated septic systems, industrial waste water and agricultural drainage.

Geochemistry of Stable Isotopes
Stable isotopic data measured for the groundwater and Ismailia Canal water are  Table 2. The δ values vary greatly in the Quaternary aquifer, ranging from −0.19‰ to 5.16‰ for oxygen-18 and from 3.4‰ to 34‰ for deuterium.
There being a general tendency of increase of δ values toward the west (under the cultivated land) parallel to the direction of flow. The heterogeneous isotopic contents in the groundwater of the aquifer may suggest the contribution from others water resources, either surface or subsurface waters.
The δ 18 O and δ 2 H values of water samples are plotted on a classical δ 18 O and δ 2 H diagram (Figure 9(a)). The isotopic compositions of the old Nile water [38], irrigation return flow [39] and Miocene aquifer [40] are included in the diagram for comparison. The old Nile water is a term denoting to the water that is recharged to the Nile aquifer system from the Nile floods occurring before the construction of Aswan High Dam of Egypt in 1963 [41]. Therefore, it is depleted in its isotopic composition comparing with that of the modern Nile water after the construction of the High Dam. of evaporation, where the slope and intercept are found to be less than those of the WMWL described by the equation δ 2 H = 8δ 18 O + 10‰ [42]. The evaporation trend is greatly consistent with the mixing in the aquifer between the old Nile water and the surplus water of irrigation (Figure 9(a)). The aforementioned two groups of waters (groups A and B) are also distinguished on the δ 18 O-δ 2 H diagram ( Figure 9). The first group (group A) includes the groundwater samples 1,2,8,9,14,23,30, and 31 and has isotopic composition ranging from −0.19‰ to 3.28‰ for oxygen-8 and from 3.4‰ to 27.99‰ for deuterium. The groundwater of this group is less affected by evaporation.

Quality of Groundwater for Drinking
The calculated water quality index values, WQI (Table 5)

Quality of Groundwater for Domestic Uses
The water quality index (WQI) values calculated for the groundwater samples (  Figure 10(c)).

Quality of Groundwater for Irrigation Uses
The water quality index (WQI) is calculated only for the groundwater extracted from the wells 2, 7, 9 and 29, which are used for irrigation in the study area.
Based on the WQI values (Table 5), the water of wells 7, 29, and 2 is suitable for irrigation with slight and moderate degree of restriction on use, while the water of well 9 and Ismailia Canal is suitable without restriction.

Summary and Conclusions
The Quaternary aquifer is the second largest source of potable water in the densely populated area of Northeast Cairo, Egypt. The area contains several   industrial facilities, and it has been selected to accommodate a number of new oil refinery units. Information dealing with the groundwater conditions in the area is very scarce. This work presented groundwater baseline data that is vital and necessary before starting the operation of the new industrial projects. Geochemistry of the groundwater was investigated using an integrated approach including the hydrogeological, hydrochemical and isotopic tools. The relation between surface water and groundwater bodies was explored. The effects of natural and anthropogenic factors on the chemistry of groundwater were detected. The water quality indices were determined to assess quality of groundwater for different uses.
The Quaternary aquifer is mainly formed of sands, gravels with clay lenses and carbonaceous materials. The groundwater is shallow and exists under semi confining conditions. The direction of groundwater movement is towards the cultivated and industrial areas. The groundwater has alkaline nature (7.5 < pH < Most groundwater samples show high levels of Mn and Al elements. Two water groups showing two different evolutionary trends in the aquifer are distinguished from the relations between the hydrochemical and stable isotopic (δ 18 O and δ 2 H) parameters. The chemical quality of groundwater is affected by both the natural processes (weathering, dissolution and ion exchange) and human factors (agricultural and industrial activities). High levels of nitrate, manganese and aluminum that exceed the maximum permissible limits for drinking purpose are recorded in some sites. The calculated nitrate pollution index (NPI) reveals that about 30.30% of groundwater is polluted with nitrate, and therefore, it is unsuitable for drinking. The contamination is related to the extensive use of fertilizers for agriculture and the leakage of wastewater from improper sewage system. Moreover, the water quality indices (WQI) reveal that about 21.21% and 27.21% of groundwater, respectively, are classified as poor water for human consumption and domestic uses. The poor groundwater (the contaminated water) concentrates in the aquifer under and around the cultivated area and industrial zone as indicated from the NPI and WQI distribution maps.
The poor groundwater in the area should be treated before human consumption to exclude the concentrations of nitrate and others trace elements. The releases of wastewater from the industrial areas into sewage systems should be under control and monitored periodically. Regular observation of groundwater quality for drinking is strictly required. The improper sewage systems in some places in the urban areas must be fixed.