**4.5. Gibbs plot**

**4.4. Principal component analysis**

98 Aquifers - Matrix and Fluids

and HCO<sup>3</sup>

loading for NO<sup>3</sup>

scores for F1 and F2 (b).

applied to the hydrochemical data set (Na, K, Mg, Ca, Cl, SO<sup>4</sup>

**Table 2.** Correlation matrix of the 22 physicochemical parameters.

The principal component analysis (PCA), which is widely used in environmental studies, exhibits complex associations among several variables and individuals [17, 18]. Factors analysis was

BouHafna and Haffouz aquifers in order to precisely specify the main processes controlling the groundwater mineralization (**Figure 6a**). The PCA approach has preserved only the first two factors, which represent 74.63% of total samples variance (62.77% for F1 and 11.86% for F2). In the variables space, the F1 factor displays strong positive loadings for Na, K, Mg, Ca, Cl, SO<sup>4</sup>

and TDS. The strong correlations for the referred major ions suggest that the groundwater mineralization is acquired through water-rock interaction processes. The positive loading for NO<sup>3</sup>

reflect the influence of the return flow of irrigation water as a potential source of contamination related to the application of fertilizers. The F2 factor takes positive loadings for pH and negative

tor lends support to the implication of the denitrification process in the groundwater salinization.

**Figure 6.** Variable space deduced from the geochemical PCA (a); cluster analysis main sample groups according to their

. The inverse relationship between pH and NO<sup>3</sup>

, HCO<sup>3</sup>

, NO<sup>3</sup>

, EC, and TDS) of

with respect to F2 fac-

, NO<sup>3</sup> ,

may

Gibbs plot is used in the present investigation to confirm the significant role played by the natural hydrochemical processes already cited and their effect on groundwater quality [23]. Plot of (Na + K)/(Na + K + Ca) *versus* TDS shows that all the groundwater samples of the BouHafna and Haffouz aquifers fall in the field of water-rock interaction suggesting that the weathering of rocks is the major process that controls the groundwater mineralization in this region (**Figure 8**). Moreover, the plot of Cl/(Cl + HCO<sup>3</sup> ) *versus* TDS displays that groundwater

**Figure 7.** Schematic model showing the dedolomitization process.

**Figure 9.** The quality of groundwater in relation to salinity and sodium hazard.

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http://dx.doi.org/10.5772/intechopen.72173

101

**Figure 10.** The quality of groundwater in relation to electrical conductivity and percent sodium (Wilcox diagram).

**Figure 8.** Gibbs plots explain groundwater geochemical process in the Haffouz and BouHafna regions.

samples fall on a linear trend on the field of rock dominance with a slight tendency toward the evaporation domain, highlighting the contribution of the evaporation process to the chemical composition of groundwater in the study area. In fact, for the Bouhafna groundwater samples, evaporation greatly increases the concentration of major ions resulted from chemical weathering, leading to higher salinity [24].

#### **4.6. Suitability of groundwater for irrigation**

Several parameters can be used to determine the suitability of groundwater for irrigation, that is, the electrical conductivity (EC), sodium adsorption ratio (SAR), and percent sodium.

The plot of analytical data on the Wilcox (1955) diagram shows that 83% of groundwater samples collected from the Haffouz aquifer belong to excellent category. All groundwater samples collected from the BouHafna aquifer, and only one sample of the Haffouz aquifer falls in the field of good to permissible (**Figure 9**). These very low to low SAR and low to medium salinity suggest that the studied groundwaters are suitable to moderately suitable for irrigation purposes without any threat of imposition of any hazard. Therefore, the application of these groundwaters in irrigation will be very advantageous as it will increase the agricultural yield.

Hydrochemical Investigation and Quality Assessment of Groundwater in the BouHafna-Haffouz… http://dx.doi.org/10.5772/intechopen.72173 101

**Figure 9.** The quality of groundwater in relation to salinity and sodium hazard.

samples fall on a linear trend on the field of rock dominance with a slight tendency toward the evaporation domain, highlighting the contribution of the evaporation process to the chemical composition of groundwater in the study area. In fact, for the Bouhafna groundwater samples, evaporation greatly increases the concentration of major ions resulted from chemical

**Figure 8.** Gibbs plots explain groundwater geochemical process in the Haffouz and BouHafna regions.

Several parameters can be used to determine the suitability of groundwater for irrigation, that is, the electrical conductivity (EC), sodium adsorption ratio (SAR), and percent sodium. The plot of analytical data on the Wilcox (1955) diagram shows that 83% of groundwater samples collected from the Haffouz aquifer belong to excellent category. All groundwater samples collected from the BouHafna aquifer, and only one sample of the Haffouz aquifer falls in the field of good to permissible (**Figure 9**). These very low to low SAR and low to medium salinity suggest that the studied groundwaters are suitable to moderately suitable for irrigation purposes without any threat of imposition of any hazard. Therefore, the application of these groundwaters in irrigation will be very advantageous as it will increase the

weathering, leading to higher salinity [24].

agricultural yield.

100 Aquifers - Matrix and Fluids

**4.6. Suitability of groundwater for irrigation**

**Figure 10.** The quality of groundwater in relation to electrical conductivity and percent sodium (Wilcox diagram).

mineralization. This investigation reveals the predominance of Ca-Mg-HCO<sup>3</sup>

, Amor Ben Moussa2,3\*, SarraBel Haj Salem<sup>4</sup>

2 Research Laboratory of Environmental Science and Technologies, Tunisia 3 Laboratoire eau-membrane et biothechnologie de l'environnement, Tunisia

Extension Agriculture. Colorado: Colorado State University; 2004

4 Higher Institute of Sciences and Technology of Environment of BorjCedria, Tunisia

5 Laboratory of Radio-Analyses and Environment, National School of Engineers of Sfax,

[1] Bauder TA, Cardon GE, Waskam RM, Davis JG. Irrigation Water Quality-Cooperative

[2] Kingumbi A. Modélisation hydrogéologique d'un bassin affecté par 236 des changementsd'occupation. Cas du Merguellil en Tunisie centrale. Université de Tunis El Manar, Ecole Nationale d'ingénieurs de Tunis; 2006. Thèse de Doctorat en Génie Hydraulique

[3] EL Mejri H. Caractérisation hydrogéologique, hydro-chimique et isotopique des nappes Haffouz et Bou Hafna (Tunisie centrale). Master. Tunisie: Université de Sfax; 2010

[4] Abbes C. Etude préliminaire de la structure du Dj. Ouesselat (axe N-S Tunisie centrale); Rapport de DEA. Paris VI: Université de Pierre et Marie Curie, laboratoire de géologie

\*Address all correspondence to: amor\_geologie@yahoo.fr 1 Laboratory "Water-Energy-Environment", ENIS, Tunisia

pollution.

**Author details**

Hatem El Mejri<sup>1</sup>

**References**

University of Sfax, Sfax, Tunisia

structurale et géodynamique; 1979

water-types. These water facies are derived mainly from water-rock interaction processes, i.e., the dissolution of halite, gypsum, the dedolomitization, and the cation exchange. On the other hand, return flow of irrigation water has resulted in elevated nitrate concentrations in groundwater especially in the agricultural zones, which are characterized by an excessive use of fertilizer. Thus, it is important to protect the aquifers against overexploitation and groundwater quality deterioration related to the evaporate dissolution and agricultural contamination. For these reasons, in the BouHafna and Haffouz regions where groundwater resources are under the great development stress and environmental pressure, some preventive measures should be taken. These are (1) control the exploitation groundwater; (2) the definition of special groundwater resources protection zones; (3) control the potential processes and sources of salinization; and (4) improvement of diffuse source groundwater

Hydrochemical Investigation and Quality Assessment of Groundwater in the BouHafna-Haffouz…

and Ca-Mg-SO<sup>4</sup>

103

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and Kamel Zouari5

**Figure 11.** Doneen plot for Haffouz and BouHafna groundwater samples.

The correlation of sodium adsorption ratio (SAR) *versus* electrical conductivity shows that 55% of groundwater samples fall in the field of C3–S1, highlighting high salinity and low sodium in groundwater, which is suitable for the irrigation of all types of soil with little danger of exchangeable sodium. However, 45% of the samples fall in the field of C2–S1, reflecting low alkalinity hazard and medium salinity of groundwater. This may indicate that irrigation water can come from the referred groundwaters without danger of exchangeable sodium on all types of soils (**Figure 10**).

## **4.7. Permeability index (PI)**

The permeability index (PI) parameter was used to assess the suitability of groundwater for irrigation. Indeed, the long-term irrigation with relatively enriched Na<sup>+</sup> , Ca2+, Mg2+, and HCO<sup>3</sup> − groundwater can affect soil permeability [25]. Groundwater in the study area displays PI value ranging from 43 to 70% with an average value of 55% (PI greater than 25%) indicating that are good and suitable for irrigation purposes. Moreover, Doneen plot shows that groundwater samples in the study area fall in the fields of Class I and II, highlighting excellent to good permeability (**Figure 11**).
