The northwestern coast of Sinai is home to many economic activities and development programs, thus evaluation of the potentiality and vulnerability of water resources is important. The present work has been conducted on the groundwater resources of this area for describing the major features of groundwater quality and the principal factors that control salinity evolution. The major ionic content of 39 groundwater samples collected from the Quaternary aquifer shows high coefficients of variation reflecting asymmetry of aquifer recharge. The groundwater samples have been classified into four clusters (using hierarchical cluster analysis), these match the variety of total dissolvable solids, water types and ionic orders. The principal component analysis combined the ionic parameters of the studied groundwater samples into two principal components. The first represents about 56% of the whole sample variance reflecting a salinization due to evaporation, leaching, dissolution of marine salts and/or seawater intrusion. The second represents about 15.8% reflecting dilution with rain water and the El-Salam Canal. Most groundwater samples were not suitable for human consumption and about 41% are suitable for irrigation. However, all groundwater samples are suitable for cattle, about 69% and 15% are suitable for horses and poultry, respectively.

INTRODUCTION

Coastal areas are highly sensitive to natural or anthropogenic effects. The northwestern coast of Sinai (site of the study area; Figure 1) is home to many economic activities: industry, agriculture, tourism, fisheries, trading and other development programs.
Figure 1

Location map of the collected groundwater samples, northwest Sinai.

Figure 1

Location map of the collected groundwater samples, northwest Sinai.

Securing water resources of appropriate quantity and quality is of prime importance for development programs in this important sector. This emphasises the importance of evaluation of the sustainability, potentiality and vulnerability of water resources from a development perspective.

The annual rainfall in the study area is limited; it varies between 26 and 54.8 mm and the total quantity of rainfall generally increases northward (El-Sheikh 2008). The national project of the El-Salam Canal has been started and River Nile water is being carried to Sinai. According to the Ministry of Water Resources and Irrigation (1991, 2009) and Hafez (2005), it is expected that the Nile water supply to this area will not fulfill the requirements of all the planned projects. Therefore, the demand for freshwater supplies has accordingly increased and attention is focused on groundwater utilization as an alternative or additive to rainfall.

The quality of groundwater resources in coastal zones is affected by many constraints (natural and/or anthropogenic). These include seawater intrusion, rock/water interaction, evaporation, irrigation return and drainage water effects, etc. Identifying the principal factors that control the salinity evolution and water quality aspects helps to achieve sustainable use of coastal resources.

This paper describes the prevailing groundwater conditions in the northwestern coastal zone of Sinai and explores the attributes of water quality and the controlling processes. The chemometric multivariate analysis has been performed to define the principal water quality components that account for much of the variability in the system under study.

Study area

Geomorphologically, northwestern Sinai is characterized by the presence of a coastal plain, lakes such as Malaya and Al-Bardawil, salt marshes and Sabkha (salt flats) such as those located around Al-Bardawil Lake and Sahel Al-Tina, and sand dunes (compiled after Elwan et al. 1983; Geological Survey of Egypt 1992; Yousef & El-Shenawy 2000). Figure 2 shows the distribution of the geomorphological features in the northwest of Sinai.
Figure 2

Geomorphological map of northwestern Sinai (compiled after Elwan et al. 1983; Geological Survey of Egypt 1992; Yousef & El-Shenawy 2000).

Figure 2

Geomorphological map of northwestern Sinai (compiled after Elwan et al. 1983; Geological Survey of Egypt 1992; Yousef & El-Shenawy 2000).

Geologically, northwestern Sinai is covered by Quaternary rocks around Pleistocene and Holocene (after Geological Survey of Egypt 1992), as shown in Figure 3.
Figure 3

Geological map of northwest Sinai, Egypt (after Geological Survey of Egypt 1992).

Figure 3

Geological map of northwest Sinai, Egypt (after Geological Survey of Egypt 1992).

Hydrogeologically, the Quaternary deposits constitute the major water-bearing formations in northwestern Sinai (Geological Survey of Egypt 1992). These deposits consist mainly of loose sands with a few clay intercalations. The groundwater exists under a free water table condition with the depth to water varying from 0.5 m in the northwest to 9.1 m in the southeast. The water table ranges from −3.7 to 10 mas (Embaby & El-Barbary 2011).

MATERIALS AND METHODS

Thirty-nine groundwater samples tapping the Quaternary aquifer were collected from the study area, as shown in Figure 1. These water samples were subjected to both field and laboratory analyses. The field analyses include electrical conductivity (EC) (μS/cm) and pH, which has been measured using an EC meter and a pH meter (Jenway, model 3150).

The laboratory analyses include the determination of major ions (Na+, K+, Mg2+, Ca2+, Cl, , , and ). Chloride, calcium, carbonate and bicarbonate were determined using a titrimetric method. Sulfate ion concentration was determined calorimetrically using the turbidity method (USEPA 1979) by UV/visible spectrophotometer. Sodium and potassium content were measured by flame photometer, according to Rhoades (1982).

The results of the chemical analysis are expressed in milligram per liter (mg/l). The multivariate statistical analyses of the chemical parameters were conducted using SPSS (software 22 version).

The GALDIT index has been combined with geographic information system (GIS) tool to evaluate the vulnerability of groundwater aquifer to seawater intrusion.

RESULTS AND DISCUSSION

Hydrochemical characterization

The results of hydrochemical analyses of the studied groundwater samples are shown in Table 1. These results have been statistically treated and their coefficient of variation are calculated. The coefficients of variation of the six hydrochemical parameters, Na+, K+, Cl, Ca2+, Mg2+ and , are equal to 0.63, 0.69, 0.53, 0.68, 0.73 and 0.49, respectively; these values are relatively high indicating heterogeneity in aquifer recharge and salinization processes.

Table 1

Results of hydrochemical analyses of groundwater samples

ID EC at 25 °C (mmohs/cm) TDS (mg/l) pH K+ (mg/l) Na+ (mg/l) Mg2+ (mg/l) Ca2+ (mg/l) Cl (mg/l) SO42− (mg/l) CO32− (mg/l) HCO3 (mg/l) 
10.56 6,566 8.19 56.5 2,179 56 200 3,403 470 201 
5.25 3,549 7.87 38.3 631 168 333 1,787 324 268 
0.81 820 7.47 19.3 86 12 116 68 143 376 
19.75 9,384 7.44 80.4 2,902 58 481 4,756 905 201 
6.32 4,385 7.54 41.5 1,190 67 220 2,042 556 268 
7.27 3,799 7.5 15.3 614 316 301 1,702 717 134 
8.81 6,697 7.08 18.6 1,961 255 80 3,403 784 195 
9.02 5,783 7.26 20 1,534 340 100 3,063 584 141 
6.08 4,505 7.14 18.6 1,210 103 301 2,042 629 201 
10 5.92 4,296 7.92 17.2 1,091 95 341 1,906 686 161 
11 5.78 3,808 7.34 15.3 894 109 293 1,702 660 134 
12 4.93 4,443 7.6 20.1 931 272 252 2,246 600 121 
13 7.22 3,895 7.42 14.4 759 122 441 1,634 724 201 
14 16.57 8,697 27.2 2,591 407 20 4,254 1,270 128 
15 6.32 4,242 6.9 15.7 635 365 361 2,042 622 201 
16 6.22 3,760 7.34 20 635 304 200 1,872 581 148 
17 4.75 3,329 7.67 12.5 865 80 212 1,566 473 121 
18 4.92 3,614 7.27 17.9 802 134 301 1,702 457 201 
19 9.2 3,152 7.26 31.6 319 105 557 1,361 644 134 
20 15.1 6,495 6.84 61.3 1,613 95 541 3,063 987 134 
21 2.05 2,072 7.4 15.4 432 80 160 817 159 52.8 356 
22 7.17 5,280 7.45 12.3 1,451 85 381 2,723 454 175 
23 0.67 692 7.59 13.1 95 29 100 78 108 66 268 
24 5,692 7.5 15.3 1,795 90 224 3,063 343 161 
25 10.06 7,707 7.18 23.6 1,923 523 40 4,084 771 342 
26 11.63 7,752 7.05 19.3 1,279 365 1,002 4,186 733 168 
27 11.04 7,165 7.12 13.4 1,915 97 581 3,744 613 201 
28 11.45 4,777 7.14 26.8 513 231 761 2,174 883 188 
29 11.24 5,315 7.07 13.8 749 352 661 2,772 619 148 
30 6.03 4,200 7.36 22.9 535 219 641 2,178 416 188 
31 16.9 8,600 6.91 40.8 1,620 462 782 4,171 1,337 188 
32 6.18 4,609 7.2 15 695 182 701 2,314 533 168 
33 5.51 2,337 7.39 8.5 297 149 313 956 479 134 
34 1.86 1,800 7.78 8.6 281 135 140 608 298 329 
35 2.03 2,837 7.76 3.1 869 46 76 1,361 213 268 
36 9.12 6,408 7.29 19.3 1,745 122 501 3,335 559 128 
37 9.79 7,703 6.89 16.2 2,064 277 473 4,084 654 106 134 
38 1.2 954 7.82 7.9 264 20 102 140 416 
39 15.93 8,257 7.28 17.7 1,821 397 573 3,948 1,340 161 
ID EC at 25 °C (mmohs/cm) TDS (mg/l) pH K+ (mg/l) Na+ (mg/l) Mg2+ (mg/l) Ca2+ (mg/l) Cl (mg/l) SO42− (mg/l) CO32− (mg/l) HCO3 (mg/l) 
10.56 6,566 8.19 56.5 2,179 56 200 3,403 470 201 
5.25 3,549 7.87 38.3 631 168 333 1,787 324 268 
0.81 820 7.47 19.3 86 12 116 68 143 376 
19.75 9,384 7.44 80.4 2,902 58 481 4,756 905 201 
6.32 4,385 7.54 41.5 1,190 67 220 2,042 556 268 
7.27 3,799 7.5 15.3 614 316 301 1,702 717 134 
8.81 6,697 7.08 18.6 1,961 255 80 3,403 784 195 
9.02 5,783 7.26 20 1,534 340 100 3,063 584 141 
6.08 4,505 7.14 18.6 1,210 103 301 2,042 629 201 
10 5.92 4,296 7.92 17.2 1,091 95 341 1,906 686 161 
11 5.78 3,808 7.34 15.3 894 109 293 1,702 660 134 
12 4.93 4,443 7.6 20.1 931 272 252 2,246 600 121 
13 7.22 3,895 7.42 14.4 759 122 441 1,634 724 201 
14 16.57 8,697 27.2 2,591 407 20 4,254 1,270 128 
15 6.32 4,242 6.9 15.7 635 365 361 2,042 622 201 
16 6.22 3,760 7.34 20 635 304 200 1,872 581 148 
17 4.75 3,329 7.67 12.5 865 80 212 1,566 473 121 
18 4.92 3,614 7.27 17.9 802 134 301 1,702 457 201 
19 9.2 3,152 7.26 31.6 319 105 557 1,361 644 134 
20 15.1 6,495 6.84 61.3 1,613 95 541 3,063 987 134 
21 2.05 2,072 7.4 15.4 432 80 160 817 159 52.8 356 
22 7.17 5,280 7.45 12.3 1,451 85 381 2,723 454 175 
23 0.67 692 7.59 13.1 95 29 100 78 108 66 268 
24 5,692 7.5 15.3 1,795 90 224 3,063 343 161 
25 10.06 7,707 7.18 23.6 1,923 523 40 4,084 771 342 
26 11.63 7,752 7.05 19.3 1,279 365 1,002 4,186 733 168 
27 11.04 7,165 7.12 13.4 1,915 97 581 3,744 613 201 
28 11.45 4,777 7.14 26.8 513 231 761 2,174 883 188 
29 11.24 5,315 7.07 13.8 749 352 661 2,772 619 148 
30 6.03 4,200 7.36 22.9 535 219 641 2,178 416 188 
31 16.9 8,600 6.91 40.8 1,620 462 782 4,171 1,337 188 
32 6.18 4,609 7.2 15 695 182 701 2,314 533 168 
33 5.51 2,337 7.39 8.5 297 149 313 956 479 134 
34 1.86 1,800 7.78 8.6 281 135 140 608 298 329 
35 2.03 2,837 7.76 3.1 869 46 76 1,361 213 268 
36 9.12 6,408 7.29 19.3 1,745 122 501 3,335 559 128 
37 9.79 7,703 6.89 16.2 2,064 277 473 4,084 654 106 134 
38 1.2 954 7.82 7.9 264 20 102 140 416 
39 15.93 8,257 7.28 17.7 1,821 397 573 3,948 1,340 161 

The results of chemical analysis have been used to identify the hydrochemical characteristics and salinization processes of the groundwater under study and to evaluate its quality aspects. The water types of the studied samples are classified into six major groups as follows.

Samples of Cl-Na, Cl-Ca, and Cl-Mg water types dominate 72%, 15.4% and 2.5%, respectively, of all samples and represent the highest mineralized water which may develop through leaching and dissolution of marine sediments, cation exchange and/or seawater intrusion.

Samples of HCO3-Ca, HCO3-Na, and SO4-Na water types dominate a total of 10.1% of all samples; these are located in the renewable recharge area close to the irrigation canals.

The distribution of the points of the groundwater samples on a Piper diagram (Figure 4) shows that more than 90% of them occupy the zone of extremely high SO4 + Cl concentration with ratios of (Na/Ca + Mg) in the range of (20% to 80%). The remainder of the samples occupy a zone of more freshwater with and Ca + Mg dominance.
Figure 4

The distribution of groundwater samples on a Piper diagram.

Figure 4

The distribution of groundwater samples on a Piper diagram.

Multivariate statistical analysis

Real hydrochemical data often contain some less important parameters besides the ones which encode important information about the quality (Malinowski & Howery 1980; Malinowski 1991; Lavine 2000; Jolliffe 2002; Praus 2005). Multivariate statistical analysis of the chemical analysis data has been conducted using SPSS program Version 22.0. This helps to infer the principal parameters that control the salinity and the quality of the groundwater under study.

Hierarchical cluster analysis

The studied groundwater samples have been classified according to the proximity of the water quality parameters into four major clusters, A, B, C and D (Figure 5). These comprise the samples numbers A = (3, 23, 38, 21, 34, and 33), B = (5, 9, 10, 12, 15, 30, 28, 32, 6, 16, 11, 13, 2, 18, 17, 19, 35), C = (1, 7, 20, 36, 8, 24, 22, and 29) and D = (4, 14, 31, 39, 25, 37, 27, and 26). The clustering of these samples is based on total dissolved solids (TDS) and ionic composition which are controlled by hydrogeochemical and physicochemical conditions. The TDS (ppm) of A, B, C and D clusters vary in the ranges (692–2,337), (2,837–4,777), (5,280–6,697) and (7,165–9,384), respectively. This is correlated with an increase of (Cl, Na) on account of (SO4, Ca) and (HCO3, Ca) from A to B to C to D.
Figure 5

Hierarchical clustering analysis of groundwater samples in the study area.

Figure 5

Hierarchical clustering analysis of groundwater samples in the study area.

Principal component analysis

Two principal components have been defined as best descriptors of the variability of chemical composition of the groundwater samples under study. These express about 72% of the variance as indicated in Table 2.

Table 2

Total variance explained

Component Initial eigenvalues
 
Extraction sums of squared loadings
 
Total % of variance Cumulative % Total % of variance Cumulative % 
4.485 56.067 56.067 4.485 56.067 56.067 
1.266 15.825 71.892 1.266 15.825 71.892 
0.952 11.903 83.795    
0.646 8.080 91.876    
0.445 5.560 97.436    
0.203 2.537 99.973    
0.002 0.026 100.000    
8.275 × 10−6 0.000 100.000    
Component Initial eigenvalues
 
Extraction sums of squared loadings
 
Total % of variance Cumulative % Total % of variance Cumulative % 
4.485 56.067 56.067 4.485 56.067 56.067 
1.266 15.825 71.892 1.266 15.825 71.892 
0.952 11.903 83.795    
0.646 8.080 91.876    
0.445 5.560 97.436    
0.203 2.537 99.973    
0.002 0.026 100.000    
8.275 × 10−6 0.000 100.000    

Extraction method = Principal component analysis.

The first component represents about 56% of the variance and combines the chemical variables TDS, Cl, SO4, Na and Ca; the second component represents about 15.8% of the variance and combines K, Na and HCO3. The weighting values of the specific parameters on the corresponding principal component are indicated in Table 3. These values represent their effective role on the ionic composition and water quality. The salinization processes that could contribute to the distribution of the first component parameters are evaporation, leaching/dissolution of marine salts and seawater intrusion, while dilution with rain water and the El-Salam Canal could be responsible for the second component.

Table 3

Component matrixa of the chemical data

  Component
 
TDS 0.975 0.126 
0.509 0.589 
Na 0.827 0.457 
Mg 0.599 −0.464 
Ca 0.480 −0.492 
Cl 0.960 0.119 
SO4 0.867 −0.172 
HCO3 −0.573 0.439 
  Component
 
TDS 0.975 0.126 
0.509 0.589 
Na 0.827 0.457 
Mg 0.599 −0.464 
Ca 0.480 −0.492 
Cl 0.960 0.119 
SO4 0.867 −0.172 
HCO3 −0.573 0.439 

aTwo components extracted from matrix; Extraction method = Principal component analysis; Loadings greater than 0.3 are in bold.

Salinization processes

The general geochemical features of the studied groundwater samples and the chemometric multivariate analysis highlighted the possible salinization processes that might contribute to salt composition and water quality. To put more emphasis on this subject, three mechanisms of salinization have been checked as outlined below.

Dissolution/precipitation processes

To determine the possibility of dissolution/precipitation on salinization processes in the study area, the saturation index of the groundwater samples with respect to the relevant salts in the system (calcite, dolomite, anhydrite, halite and gypsum) has been calculated using the SOLMINEQ program (SOLMINEQ.GW 1999).

Table 4 reveals that about 90% of the groundwater samples are oversaturated with respect to dolomite and calcite, reflecting a tendency for precipitation. On the other hand, the groundwater samples are undersaturated with respect to gypsum, anhydrite and halite, reflecting a tendency for continuing dissolution of these salts from the aquifer matrix.

Table 4

Saturation indices of collected groundwater samples using (SPSS 22 software)

Sample ID Anhydrite Calcite Dolomite Gypsum Halite 
−1.453 0.929 2.653 −1.166 −3.884 
−1.276 1.03 3.103 −0.988 −4.662 
−1.629 0.548 1.431 −1.339 −6.847 
−0.937 0.511 1.453 −0.651 −3.649 
−1.222 0.517 1.852 −0.934 −4.339 
−1.053 0.287 1.928 −0.765 −4.709 
−1.679 −0.585 0.676 −1.392 −3.937 
−1.694 −0.433 1.01 −1.406 −4.081 
−1.075 0.117 1.104 −0.787 −4.338 
10 −0.977 0.834 2.446 −0.688 −4.411 
11 −1.009 0.22 1.341 −0.721 −4.539 
12 −1.176 0.301 1.972 −0.888 −4.416 
13 −0.911 0.351 1.477 −0.623 −4.628 
14 −2.413 −1.288 0.084 −2.127 −3.738 
16 −1.267 0.141 1.798 −0.978 −4.65 
17 −1.165 0.394 1.694 −0.877 −4.579 
18 −1.147 0.059 1.102 −0.858 −4.58 
19 −0.75 0.347 1.298 −0.461 −5.075 
20 −0.751 −0.172 0.24 −0.464 −4.069 
21 −1.703 0.593 2.219 −1.414 −5.123 
22 −1.153 0.454 1.599 −0.865 −4.144 
23 −1.826 0.634 2.055 −1.537 −6.744 
24 −1.504 0.244 1.439 −1.216 −4.003 
25 −2.082 −0.583 1.299 −1.796 −3.882 
26 −0.753 0.345 1.606 −0.466 −4.056 
27 −0.953 0.314 1.199 −0.666 −3.912 
28 −0.633 0.434 1.687 −0.345 −4.699 
29 −0.893 0.192 1.458 −0.605 −4.438 
30 −0.988 0.615 2.108 −0.7 −4.668 
31 −0.63 0.125 1.368 −0.344 −3.964 
32 −0.859 0.434 1.626 −0.571 −4.534 
33 −1.05 0.275 1.556 −0.761 −5.238 
34 −1.502 0.751 2.815 −1.212 −5.435 
35 −1.929 0.385 1.886 −1.641 −4.614 
36 −1.027 0.24 1.213 −0.74 −3.994 
37 −1.077 0.21 1.54 −0.79 −3.852 
38 −2.368 0.175 0.973 −2.078 −6.184 
39 −0.73 0.305 1.795 −0.443 −3.932 
Sample ID Anhydrite Calcite Dolomite Gypsum Halite 
−1.453 0.929 2.653 −1.166 −3.884 
−1.276 1.03 3.103 −0.988 −4.662 
−1.629 0.548 1.431 −1.339 −6.847 
−0.937 0.511 1.453 −0.651 −3.649 
−1.222 0.517 1.852 −0.934 −4.339 
−1.053 0.287 1.928 −0.765 −4.709 
−1.679 −0.585 0.676 −1.392 −3.937 
−1.694 −0.433 1.01 −1.406 −4.081 
−1.075 0.117 1.104 −0.787 −4.338 
10 −0.977 0.834 2.446 −0.688 −4.411 
11 −1.009 0.22 1.341 −0.721 −4.539 
12 −1.176 0.301 1.972 −0.888 −4.416 
13 −0.911 0.351 1.477 −0.623 −4.628 
14 −2.413 −1.288 0.084 −2.127 −3.738 
16 −1.267 0.141 1.798 −0.978 −4.65 
17 −1.165 0.394 1.694 −0.877 −4.579 
18 −1.147 0.059 1.102 −0.858 −4.58 
19 −0.75 0.347 1.298 −0.461 −5.075 
20 −0.751 −0.172 0.24 −0.464 −4.069 
21 −1.703 0.593 2.219 −1.414 −5.123 
22 −1.153 0.454 1.599 −0.865 −4.144 
23 −1.826 0.634 2.055 −1.537 −6.744 
24 −1.504 0.244 1.439 −1.216 −4.003 
25 −2.082 −0.583 1.299 −1.796 −3.882 
26 −0.753 0.345 1.606 −0.466 −4.056 
27 −0.953 0.314 1.199 −0.666 −3.912 
28 −0.633 0.434 1.687 −0.345 −4.699 
29 −0.893 0.192 1.458 −0.605 −4.438 
30 −0.988 0.615 2.108 −0.7 −4.668 
31 −0.63 0.125 1.368 −0.344 −3.964 
32 −0.859 0.434 1.626 −0.571 −4.534 
33 −1.05 0.275 1.556 −0.761 −5.238 
34 −1.502 0.751 2.815 −1.212 −5.435 
35 −1.929 0.385 1.886 −1.641 −4.614 
36 −1.027 0.24 1.213 −0.74 −3.994 
37 −1.077 0.21 1.54 −0.79 −3.852 
38 −2.368 0.175 0.973 −2.078 −6.184 
39 −0.73 0.305 1.795 −0.443 −3.932 

For further insights into dissolution of gypsum, anhydrite and halite, the relationships of Na+ vs Cl, and Ca2+ vs , have been constructed as shown in Figures 6 and 7. These show quite a direct distribution with high correlation indicating that the dissolution of both halite and gypsum could contribute to the groundwater salinization. The sample points show some deviation below the 1:1 line in the Na+ vs Cl relationship in Figure 6 and above the 1:1 line in the Ca + Mg relationship in Figure 7. This might be attributed to the cation exchange process which will be discussed in the next section.
Figure 6

Na+ vs Cl relationship.

Figure 6

Na+ vs Cl relationship.

Figure 7

Ca2+ vs relationship.

Figure 7

Ca2+ vs relationship.

Ion exchange reaction

Ion exchange reactions involve the replacement of one ion for another at the surface of a particle in the hydraulic system. Clay minerals have negatively charged surfaces, so they attract cations to balance the electrical charge and maintain electrical neutrality. The ion exchange process was checked by plotting a relation between against (Na+-Cl) (Jankowski et al. 1998; Figure 8). The water samples were plotted on a line of a slope equal −1 in the upper left square of the figure. This indicates that the Quaternary groundwater samples are affected by reverse ion exchange reactions where saline water invades fresh water in the aquifer leading to sodium adsorption and Ca and Mg release.
Figure 8

Relationship between Ca + Mg-HCO3-SO4 versus Na-Cl for the Quaternary aquifer samples.

Figure 8

Relationship between Ca + Mg-HCO3-SO4 versus Na-Cl for the Quaternary aquifer samples.

Seawater intrusion

To check the potential of seawater intrusion as a salinization process acting on the groundwater under study, the GALDIT index (Chachadi & Lobo-Ferreira 2001), one of the weighting/rating driven indicators, has been used. It is determined based on six hydrogeochemical, hydrogeological and physical parameters inherent in the groundwater system. These parameters are as follows: (i) groundwater occurrence (aquifer type; unconfined, confined and semi-confined); (ii) aquifer hydraulic conductivity; (iii) the level of groundwater relative to sea level; (iv) distance from the shore (distance inland perpendicular from the shoreline); (v) impact on existing status of seawater intrusion in the area; and (vi) the thickness of the aquifer being mapped.

Each of the indicated factors has been assigned a weighting and rating scores as indicated in Table 5. Based on the values of these scores an overall GALDIT index is calculated as follows: 
formula
1
where W1–W6, and GR, AR, LR, DR, IR and TR are the weighting and rating values of the six parameters, respectively. The classification of groundwater vulnerability according to the ranges of GALDIT index is indicated in Table 5.
Table 5

Rating and weighting values of different hydrogeological parameters according to their relative importance (Chachadi & Lobo-Ferreira 2001)

Indicator Weight Indicator variables
 
Rating 
Class Range 
Groundwater occurrence/aquifer type Confined   10 
Unconfined 7.5 
Leaky confined 
Bounded confined (Recharge and or impervious boundary aligned 2.5 
Aquifer hydraulic conductivity (m/day) High >40 10 
Medium 10–40 7.5 
Low 5–10 
V. low <5 2.5 
Height of groundwater level (amsl)(m) High <1 10 
Medium 1–1.5 7.5 
Low 1.5–5 
V. low >5 2.5 
Distance from shore/high tide (m) V. small <500 10 
Small 500–750 7.5 
Medium 750–1,000 
Fair >1,000 2.5 
Impact status of existing sea water intrusion High >2 10 
Medium 1.5–2 7.5 
Low 1–1.5 
V. low <1 2.5 
Saturated aquifer thickness (m) High >10 10 
Medium 7.5–10 7.5 
Low 5–7.5 
V. low <5 2.5 
Indicator Weight Indicator variables
 
Rating 
Class Range 
Groundwater occurrence/aquifer type Confined   10 
Unconfined 7.5 
Leaky confined 
Bounded confined (Recharge and or impervious boundary aligned 2.5 
Aquifer hydraulic conductivity (m/day) High >40 10 
Medium 10–40 7.5 
Low 5–10 
V. low <5 2.5 
Height of groundwater level (amsl)(m) High <1 10 
Medium 1–1.5 7.5 
Low 1.5–5 
V. low >5 2.5 
Distance from shore/high tide (m) V. small <500 10 
Small 500–750 7.5 
Medium 750–1,000 
Fair >1,000 2.5 
Impact status of existing sea water intrusion High >2 10 
Medium 1.5–2 7.5 
Low 1–1.5 
V. low <1 2.5 
Saturated aquifer thickness (m) High >10 10 
Medium 7.5–10 7.5 
Low 5–7.5 
V. low <5 2.5 
The data required for calculating the GALDIT index has been explored from 24 wells distributed across the study area. The (GIS) tool has been used for constructing thematic maps for different parameters of the index and superimposing them as layers to derive the final map. The following reviews the explored data and the corresponding rating of the GALDIT index in the study area. (i) Groundwater Occurrence in the studied aquifer is mainly under unconfined conditions which give more opportunities for seawater intrusion than confined and semi-confined. According to Table 5, the rating score assigned to the groundwater occurrence in the study area is 7.5. (ii) Aquifer Hydraulic Conductivity has a high influence on the magnitude of seawater front movement; the higher the conductivity is, the higher is the inland movements of the seawater front. The hydraulic conductivity that corresponds to the lithologic composition of the water-bearing formation in the study area has values from 3 m/day at the west (at El-Tina Plain) to about 10 m/day at Bir El-Abd, (Omar 2011). The rating of this parameter is illustrated in Figure 9. (iii) The level of groundwater above sea level is a very important factor in evaluating seawater intrusion because it determines the availability of hydraulic pressure to push the seawater front back. The ground water level from Embaby & El-Barbary (2011) assigns the rating values shown in Figure 9. (iv) Distance from the shore of the sampled groundwater wells assigns an average rating value of about 2.5. (v) Impact on the existing status of seawater intrusion: Chachadi & Lobo-Ferreira (2001) recommended using the ratio of as the criterion to evaluate the impact of the existing status of seawater intrusion into the coastal aquifers. The results of the hydrochemical analysis of the collected groundwater samples have been used to calculate the ratio of . The corresponding cartographic rating assigned the spatial distribution of the calculated ratio is indicated in Figure 9. (vi) The thickness of the aquifer being mapped: the thickness of the shallow unconfined aquifer in the study area ranges from 5 to 50 m. The rating of this parameter is illustrated in Figure 9.
Figure 9

GALDIT result: (a) impact status of existing seawater intrusion; (b) distance from shore; (c) aquifer hydraulic conductivity (m/day); (d) height of groundwater level (amsl)(m); (e) saturated aquifer thickness (m); (f) groundwater occurrence/aquifer type; (g) GALDIT index.

Figure 9

GALDIT result: (a) impact status of existing seawater intrusion; (b) distance from shore; (c) aquifer hydraulic conductivity (m/day); (d) height of groundwater level (amsl)(m); (e) saturated aquifer thickness (m); (f) groundwater occurrence/aquifer type; (g) GALDIT index.

The overall GALDIT index has been calculated using Equation (1). It has been used to classify the study area according to its vulnerability to seawater intrusion. The computed GALDIT index of the studied groundwater samples has values in the range 2.5–7.5 (Figure 9). Based on Table 6, about 71% of the study area is of low seawater intrusion vulnerability and about 29% is of medium seawater vulnerability as a result of marine water associating Sabkha.

Table 6

Rating and weighting values of different hydrogeological parameters according to their relative importance

GALDIT index range Vulnerability classes 
>7.5 High vulnerability 
5–7.5 Moderate vulnerability 
<5 Low vulnerability 
GALDIT index range Vulnerability classes 
>7.5 High vulnerability 
5–7.5 Moderate vulnerability 
<5 Low vulnerability 

Water quality evaluation

The evaluation of groundwater quality for various uses (drinking by both humans and livestock, as well as irrigation) is mainly based on TDS and major ions concentration in comparison with the recommended limits given in the standards for the different uses.

Evaluation of groundwater for drinking by humans

According to the Egyptian standards for drinking and domestic uses adapted from Higher Committee for Water (1995) (Table 7), about only 10% of the collected groundwater samples can be used for human drinking and the rest can not be used because their TDS and major ion concentrations exceed the permissible limits.

Table 7

Egyptian standards for drinking and domestic uses

Chemical constituent Max. permissible limit in mg/l 
Calcium 200 
Chloride 500 
Hardness as CaCO3 500 
Magnesium 150 
Nitrate 10 
TDS 1,200 
Sodium 200 
Sulphate 250–400 
pH 6.5–9.2 
Chemical constituent Max. permissible limit in mg/l 
Calcium 200 
Chloride 500 
Hardness as CaCO3 500 
Magnesium 150 
Nitrate 10 
TDS 1,200 
Sodium 200 
Sulphate 250–400 
pH 6.5–9.2 

Evaluation of groundwater for drinking by livestock and poultry

Water to be used for livestock and poultry is subject to quality limitations like those for human consumption. According to the upper limits of concentration for stock and poultry water, shown in Table 8, it appears that nearly all the groundwater samples in the studied area are suitable for the drinking by cattle (dairy) and about 69% and 15% are suitable for horses and poultry, respectively.

Table 8

TDS limits for water that can be used for drinking by livestock and poultry (McKee & Wolf 1963)

Type of animal TDS (mg/l) 
Poultry 2,860 
Horses 6,335 
Cattle (dairy) 7,150 
Cattle (beef) 10,100 
Sheep (adult) 12,900 
Type of animal TDS (mg/l) 
Poultry 2,860 
Horses 6,335 
Cattle (dairy) 7,150 
Cattle (beef) 10,100 
Sheep (adult) 12,900 

Water quality for irrigation

Water quality index (WQI) is a valuable and unique rating to depict the overall water quality status in a single term that is helpful for the selection of an appropriate treatment technique to meet the issues concerned (Chowdhury et al. 2012). An attempt has been made to use the calculated WQI values for irrigation suitability. In this study, WQI input on overall water quality deteriorations was used to achieve the pre-planned goals of this study (Rao et al. 2010; Balan et al. 2012).

WQI was based on seven important physicochemical parameters (Table 9). WQI was calculated by using the recommended standards of irrigation using the following equation: 
formula
2
where Qi is the quality rating of the ith parameter for a total of (n) water quality parameters, Vn represents values of the water quality parameter obtained from the laboratory analysis, Vi represents the ideal value of the parameter [Vi = 0, except for pH (Vi = 7) and DO (Vi = 14.6 mg/l)], and Vs represents values of the water quality parameter obtained from the recommended standard.
Table 9

Selected variables used in the WQI calculation and their recommended values (Rown et al. 1972)

Variables Maximum recommended values Wi 
TDS (mgl/L) 2,000 0.00041 
EC (μS/cm) 2,250 0.00037 
SAR 26 0.03185 
Hardness 100 0.00828 
pH 6.5–8.5 (7.5) 0.11040 
Ki 0.82799 
Na% 40 0.02070 
 sum of Wi 1.00000 
Variables Maximum recommended values Wi 
TDS (mgl/L) 2,000 0.00041 
EC (μS/cm) 2,250 0.00037 
SAR 26 0.03185 
Hardness 100 0.00828 
pH 6.5–8.5 (7.5) 0.11040 
Ki 0.82799 
Na% 40 0.02070 
 sum of Wi 1.00000 
Then, the relative (unit) weight (Wi) was calculated to be a value inversely proportional to the recommended standard (Si) for the corresponding parameter using the following relation, 
formula
3
where Wi is the relative (unit) weight for the nth parameter, Si is the recommended standard values for the nth parameter (as described in the Quality rating calculation equation), and
K is a constant of proportionality calculated using the equation, 
formula
4
Thus, the relative (unit) weights (Wi) to various water quality parameters are inversely proportional to the recommended standards for the corresponding parameters.
Finally, the overall WQI was calculated by aggregating the quality rating with the unit weight linearly by using the following equation: 
formula
5
where Qi is the quality rating and Wi is the relative weight.
Based on Table 10, the calculated values of WQI in this study were compared with the prescribed standards to show the water quality condition for agriculture purpose as represented in Figure 10.
Table 10

WQI categories and their classifications (Rown et al. 1972)

WQI Classification 
<50 Excellent 
50–100 Good 
100–200 Poor 
200–300 Bad 
>300 Unfit 
WQI Classification 
<50 Excellent 
50–100 Good 
100–200 Poor 
200–300 Bad 
>300 Unfit 
Figure 10

WQI classification for irrigation.

Figure 10

WQI classification for irrigation.

CONCLUSION

The quality of groundwater resources in the study area is stressed by both natural and anthropogenic constraints. The hydrogeochemical characteristics of the system, and multivariate statistical analysis have been used to explore the water quality and salinization processes of groundwater resources in the northwest of Sinai. It has been concluded that the the water with the highest mineralization is primarily developed through leaching and dissolution of marine sediments, cation exchange with a small contribution from marine water associating Sabkha. The water quality of the study area is generally not suitable for human drinking, although this water can be used for livestock and poultry drinking and for irrigation purposes with some limitations.

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