**4.3. Correlation matrix**

The correlation matrix of 12 parameters (Cl, NO<sup>3</sup> , SO<sup>4</sup> , HCO<sup>3</sup> , Na, K, Mg, Ca, TDS, EC, pH, and T°C) was computed in order to calculate the contribution degree of each hydrochemical parameters to the groundwater mineralization [15, 16] (**Table 2**).

Overall groundwater samples display positive and strong correlations between Cl, SO<sup>4</sup> , Na, Mg, and Ca versus TDS (>0.9), providing insight into the large contribution of these ions to BouHafna and Haffouz groundwater salinization. There is well positive correlation between Na and Cl (r = 0.84), indicating the same origin of these elements likely related to the halite dissolution. The strong and positive relationship between Ca and SO<sup>4</sup> (r = 0.98) suggests that these ions derive from the same origin probably in relation with the dissolution of gypsum and/or anhydrite. The moderate correlation between NO<sup>3</sup> and the majority of ions can be explained by an anthropogenic effect related to the pollution through return flow of irrigation water.

**Figure 5.** Piper diagram of Haffouz and BouHafna aquifers.


The projection of the 22 samples on the same first factorial plan (F1, F2) permits to classify groundwater samples into three groups (**Figure 6b**). The first group, which lies in the positive side of the first factor (F1), is mainly represented by the BouHafna groundwater samples. This group is mainly influenced by natural processes of mineralization in relation with the dissolution of evaporatic minerals, dedolomitization, and cation exchange. These processes are summarized in the schematic model, which indicates that all groundwater samples display an undersaturation state with respect to gypsum and anhydrite, suggesting that dissolution of these minerals takes place there (**Figure 7**). Supplementary concentration of Ca2+deriving from gypsum dissolution can cause calcite precipitation [19]. On the other hand, the decrease of bicarbonate concentration related to the precipitation of calcite causes the groundwater to be undersaturated with respect to dolomite and promotes the incongruent dissolution of this

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

The second group is mainly composed of BouHafna groundwater samples, which are strictly associated with intensive agricultural activities. This group, which plots in the negative side of the second factor (F2), is strongly associated with nitrate and highlights the considerable contribution of the return flow of irrigation waters to the contamination of groundwater. The third group comprises mainly the groundwater samples collected from the Haffouz aquifer. This group, which falls in the negative side of F1 and the positive side of F2, is extremely related to pH and negatively correlated with nitrate element. This position lends support to the predominance of denitrification processes, which corresponds to the biological reduction

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

) *versus* TDS displays that groundwater

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

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mineral known as dedolomitization [20–22].

) to nitrogen gas (N<sup>2</sup>

region (**Figure 8**). Moreover, the plot of Cl/(Cl + HCO<sup>3</sup>

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

).

of nitrate (NO<sup>3</sup>

**4.5. Gibbs plot**

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

#### **4.4. Principal component analysis**

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 applied to the hydrochemical data set (Na, K, Mg, Ca, Cl, SO<sup>4</sup> , HCO<sup>3</sup> , NO<sup>3</sup> , EC, and TDS) of 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> , NO<sup>3</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> may 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 loading for NO<sup>3</sup> and HCO<sup>3</sup> . The inverse relationship between pH and NO<sup>3</sup> with respect to F2 factor 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 scores for F1 and F2 (b).

The projection of the 22 samples on the same first factorial plan (F1, F2) permits to classify groundwater samples into three groups (**Figure 6b**). The first group, which lies in the positive side of the first factor (F1), is mainly represented by the BouHafna groundwater samples. This group is mainly influenced by natural processes of mineralization in relation with the dissolution of evaporatic minerals, dedolomitization, and cation exchange. These processes are summarized in the schematic model, which indicates that all groundwater samples display an undersaturation state with respect to gypsum and anhydrite, suggesting that dissolution of these minerals takes place there (**Figure 7**). Supplementary concentration of Ca2+deriving from gypsum dissolution can cause calcite precipitation [19]. On the other hand, the decrease of bicarbonate concentration related to the precipitation of calcite causes the groundwater to be undersaturated with respect to dolomite and promotes the incongruent dissolution of this mineral known as dedolomitization [20–22].

The second group is mainly composed of BouHafna groundwater samples, which are strictly associated with intensive agricultural activities. This group, which plots in the negative side of the second factor (F2), is strongly associated with nitrate and highlights the considerable contribution of the return flow of irrigation waters to the contamination of groundwater. The third group comprises mainly the groundwater samples collected from the Haffouz aquifer. This group, which falls in the negative side of F1 and the positive side of F2, is extremely related to pH and negatively correlated with nitrate element. This position lends support to the predominance of denitrification processes, which corresponds to the biological reduction of nitrate (NO<sup>3</sup> ) to nitrogen gas (N<sup>2</sup> ).
