Groundwater quality and its suitability for different uses in lower Djendjen Watershed, Northest Algeria

 

Faouzi Zahi¹, Fethi Medjani²*, Mohamed Djidel², Abdelmalek Drouiche¹

¹Geological Engineering Laboratory, University of Mohammed Seddik Benyahia Jijel, Algeria.

²Laboratory of Geology of the Sahara, University Kasdi Merbah Ouargla, Algeria.

 

ABSTRACT:

Groundwater is a vital resource in coastal areas to supply domestic, drinking, irrigation and industrial needs. To study the hydrogeochemical characteristics of groundwater and their suitability, Thirty-one (31) groundwater samples were collected from the shallow tubewells in the plain of the Djendjen river (North-East of Algeria). The water quality assessment has been carried out by evaluating the physicochemical parameters such as temperature, pH, EC, major ions i.e., Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^-, SO₄^2-, HCO₃^- and nutrients (NH₄⁺, NO₂^-, NO₃^-, PO₄^3-). The chemical parameters plotted in Piper’s diagram show the dominance of two chemical facies “calcium and sodium chloride” and “calcium bicarbonate”. Based on the analytical results, groundwater in the area is found to be generally suitable for drinking. The organic pollution index (OPI) show that the water is generally in the good quality category with no organic pollution. Chemical parameters when plotted in the U.S. Salinity diagram indicate that waters are C2S1 and C3S1 types, i.e., medium to high salinity and low sodium which is good for irrigation. Four corrosion indices were calculated (The indices include the Langelier saturation index, Ryznar stability index, Puckorius scaling index, Larson). The result indicates the corrosive nature of the majority of water samples.

 

 

 

INTRODUCTION:

Groundwater is one of the pure sources of water because it is bacteriologically free and contains more health required nutrients in the right proportion than surface water. It is estimated that approximately one third of the world’s population use groundwater for drinking purpose (Nickson et al. 2005). It can be used for both domestic and industrial purposes. However, this resource is currently at risk from various sources of contamination (Bekkoussa et al. 2013; Amadou et al. 2014; Eblin et al. 2014).

 

The quality of groundwater in a particular region is a function of physical, chemical and biological parameters that are greatly influenced by geological formations and anthropogenic activities.

 

Hydrochemistry has made significant contributions to the understanding of groundwater evolution (Li et al. 2008; Dar et al. 2014), which carries chemical signatures of recharge water and interaction with minerals and sediments forming aquifers along the flow paths as well as anthropogenic activities (Yangui et al. 2011; Monjerezi et al. 2012; Voutsis et al. 2015).

 

In the coastal alluvial plain of the Djendjen river (North-East of Algeria), Groundwater is the main source of drinking and irrigation purposes. In recent years, this region has seen an important economic development with an increase in agricultural activity and especially in livestock farming, associated with a significant demographic growth. These practices can have an influence on the regime and quality of the water. 

 

Given this context, the present paper aims to evaluate the groundwater chemistry and groundwater quality in the plain of the Djendjen river and its suitability for different uses (drinking, irrigation and industrial purposes).

 

MATERIAL AND METHODS:

Study area:

The alluvial plain of Djendjen river, located in the North-East of Algeria and belongs to the coastal plains of the Jijel region (Fig. 1), occupies the downstream part of its watershed. It is drained by Djendjen river, which has its origin in the summits of Djebel Babor. The plain is characterized by a sub-plane topography with altitudes increasing along the eastern, western and southern part of its boundaries.

 

The Djendjen plain is essentially formed by recent alluvial deposits and ancient terraces (quaternary formations), the thickness of which is variable. The recent alluvial deposits form a slightly inclined surface along the Djendjen river (Fig. 2).

 

Fig. 1: Situation of the study area

 

Fig. 2: N–S geological cross section of the study area.

 

The northern part presents current dunes occupy a band of coastline forming a cord, while the old dunes form small hills and depressions around Tassoust and Bazoul cities. The bedrock of this Quaternary aquifer is constituted by Burdigalian marls, resting on crystalline and crystallophyllian formations of the primary metamorphic substratum (Wildi, 1983). This region has subhumid climate, the precipitation values range between 800 and 900 mm/year. The monthly temperatures varies between 11 and 25°C (Boufekane et al. 2019)

 

Sampling and analytical methods:

A total of 31 groundwater samples were collected for chemistry analysis in April 2017. The sampled sites distribute throughout the alluvial plain (Fig. 3) and preserved as per the methods prescribed (Rodier et al. 2009). Parameters such as electrical conductivity (EC), pH/Eh and water temperature (T) were measured in the field using multiparameter WTW, while rests of the parameters were analysed in the Geological Engineering Laboratory (University of Jijel). Sodium (Na⁺) and Potassium (K⁺) were measured using flame photometer. The concentrations of Chlorides (Cl^-), Bicarbonates (HCO₃^-) and Calcium (Ca²⁺) were determined by titrimetry. Sulphate (SO₄^2-) is determined by spectrophotometry. Ammonium, nitrate, nitrite and phosphates ion concentrations were determined by colorimetry. The magnesium (Mg²⁺) concentration of the water analyzed is given by the difference between the total hardness and the calcium hardness Mg²⁺ = TH-Ca²⁺ (Rodier et al. 2009). All the chemical concentrations are expressed in mg/l (Table 1). To verify the analytical error of analysed ion concentration, electroneutrality (ionic balance) was computed by following equation:

        Σcation-Σanion

E = –––––––––––––– *100                 (1)

       Σcation+Σanion

Where the sum of major cations and anions are expressed in meq/L and E is the error percent/reaction error/ cationic and anionic balance. The value taken is limited to ±10% (Hem, 1975).

 

Fig. 3: Location of sampling points

 

Table 1: Statistical summary of hydrochemical parameters

 

Two diagrams were constructed to find out the different hydrochemical facies present in groundwater of the study area.

 

Piper diagram:

The analytical data obtained from the hydrochemical analysis are plotted on Piper tri-linear diagram (Piper, 1944). This diagram is used to infer hydro geochemical facies, which are distinct zones that possess cation and anion concentration categories.

 

Chadha diagram:

For the better understanding the hydrochemistry and comparing the water types Chadha´s diagram (Chadha, 1999) was plotted. The proposed diagram is a modification of Piper diagram with a view to extend its applicability in representing water analysis in the possible simplest way.

 

Water Quality Assessment:

The water quality assessment for Drinking Water Supply (DWS) was based on a comparison with the maximum admissible value of WHO (2017) for drinking purposes.

For evaluation of the water quality in terms of irrigation, sodium adsorption ratio (SAR) index is used. It is calculated by the following equation given by Richards (1954):

 

SAR=𝑁𝑎√(𝐶𝑎+𝑀𝑔)/2                           (2)

 

Where, all ion concentrations are expressed in meq/L.

SAR was plotted against EC (µS/cm) on the US salinity diagram to graphically demonstrate the feasibility of the use of this water for irrigation purposes in terms of the quality. Five (5) classes of water have been defined: excellent, good, acceptable, poor, bad (Table 2).

 

Table 2: Classification of water by degree of irrigation ability using the SAR method.

 

Water indices:

Some indices were calculated to show more the quality of water:

 

Organic Pollution Index (OPI):

This index is calculated to assess the level of the organic pollution in water, it usually depends on contents of water in ions ammonium, total nitrogen, total phosphorus and the BDO5. However, the measurement of BDO5 is not often carried out under good conditions that is why it is not used to determine the pollution level. OPI definite five (5) classes of contents for each of these parameters. The OPI is the average of the numbers of the classes of every parameter. The values of the OPI allow to distribute the organic pollutions of water in five (5) levels (Table 3).

 

 

 

Table 3: Class limits of the Organic Pollution Index (Leclercq and Vandevenne, 1987)

 

 

 

Table 4: Corrosion indices used in the study

 

RESULTS AND DISCUSSION:

Water types:

Piper diagram (Fig. 4-a) reveals a variability in the chemical facies of the waters by the dominance of calcium, magnesium and sodium for the cations and by chlorides and bicarbonates for the anions. As a result, the water is characterized by two dominant hydrochemical facies:

The first is calcium and sodium chloride facies, mainly found on the left side of the Djendjen river (Emir Abdelkader and Tassoust cities), it is a water very influenced on the one hand by anthropogenic pollution with high concentrations of chlorides, and on the other hand by the dissolution of the marl formations of the Burdugalian located on both sides of the plain. The second facies is calcium bicarbonate originates from alluvial and gypsiferous (Triassic) formations in the upstream part of the plain.

 

The Chadha’s diagram is useful for visually studying the various hydro chemical processes, such as base cation exchange, saline water and other related hydro chemical problems (Chadha, 1999). Results of analyses were plotted on the proposed diagram to show the geochemical classification of groundwater (Fig. 4-b). It is evident from the results that all samples fall in Ca–Mg–Cl Water Type.

 

Fig. 4: Water types. (a) Piper’s diagram, (b) Chadha´s diagram

 

Fig. 5: Variation of major ions. (a) Cations variation diagram. (b) Anions variation diagram

 

Water quality:

Groundwater quality for drinking purposes:

The groundwater samples had temperatures during sampling varying between 13 and 25°C. The pH ranged between 5.8 and 7.5, with an average of 6.8, indicating acidic nature. The redox potential values were in the ranged -106 –234 mV indicating a reduced environment. The electrical conductivity of groundwater in the area ranged between 325 and 1896 µS/cm with an average of 973 µS/cm.

 

The cations variation diagram (Fig. 5-a) shows that the majority of wells have concentrations that conform to the WHO standard. However, some wells have contain high calcium concentrations exceeding the recommended standard (P3, P4, P8) and high potassium values (P8), these values are mainly related to the dissolution of the alluvial and gypsiferous (Triassic) formations of the upstream part of the plain.

 

The anions variation diagram (Fig. 5-b) reveals that Chloride values are variable, with some high concentrations (exceeding the recommended standard of 250 mg/l) typically located in the center of the plain (P5, P8, P9, P11, P14, P27, P31) and generally not far from the main urban centers of the study area (Tamilla, Ain El Hamam, Tassoust, Emir Abdelkader).

 

Fig. 6: Assesment of organic pollution. (a) Nutrient parameters. (b) Organic pollution index

 

Fig. 7: Plots of groundwater samples in RIVERSIDE diagram.

 

 

The diagram of organic pollution parameters (NH₄⁺, NO₂^-, NO₃^-, PO₄^3-) show that all samples have concentrations well within the permissible limit of WHO (Fig. 6-a).

 

The organic pollution index (OPI) reveals that most of the wells are in the good quality category with no organic pollution (Fig. 6-b). Some wells are in the low to medium category. These are generally the ones with high nutrient concentrations (P5, P6, P15, P23, P29).

 

Groundwater quality for irrigation purpose:

Assessment of groundwater quality for irrigation has been analyzed using the classic diagram RIVERSIDE (Fig. 7) which is combined between the values of electrical conductivity and SAR to highlight the classes that present a danger of alkalinity.

 

Fig. 8: Corrosion indices

 

The water of the region generally is classified into two categories C2 and C3 with a medium to high risk of salinization. For The sodium hazard, the water is found confined in one groups S1, with low alkalinity hazard. Consequently, two classes can be determined: C2S1 and C3S1. As a result, all samples coming within the subfield of “Good water” category.

 

Corrosion potential level:

The result of LSI (Fig. 8-a) show that more than 74 % of samples have negative value, which shows that the waters of Djendjen plain are mostly corrosive. The values of RSI (Fig. 8-b) were more than 7 for 75 % of samples indicating the corrosive nature of these waters. The rest of the samples were slightly scaling.

 

According to the LaI (Fig. 8-c), all samples were highly corrosive, while based on the PSI (Fig. 8-d), 74% of samples show corrosive character of water.

 

CONCLUSION:

The study of the hydrogeochemical characteristics of the alluvial plain of Djendjen river has allowed to characterize the quality of the groundwater. The physicochemical analyses show that the waters have an acidic character (5.8 < pH < 7.54) with an average of 6.83. The water samples are slightly mineralized to mineralized (325 < EC < 1896 μS/cm) with an average of 973 μS/cm. The high values of the electrical conductivity are found on the right bank of the Djendjen river. The chemical quality parameters are for the most part below the standards of potability (WHO), except for a few points where chloride contents are high and sometimes exceed the accepted standard.

 

Two hydrochemical facies were identified according to Piper's diagram : (a) a calcium and sodium chloride facies characterising the waters of the left bank of Djendjen river (Emir Abdelkader to Tassoust cities), it is represented by water characterised on the one hand by anthropogenic pollution with high concentrations of chlorides and on the other hand by the dissolution of the Burdugalian marl formations located on both sides of the plain and (b) a calcium bicarbonate facies characterises the water resulting from the leaching of alluvial and gypsum formations (Triassic) from the upstream part of the plain.

 

The majority water samples are not affected by the salinity and sodium hazard, so they are suitable for irrigation purpose. By survey of corrosion indices, it was found that waters of alluvial plain of Djendjen river have corrosion potential, all the calculated indices (LSI, RSI, PSI, LaI) show this corrosion nature.

 

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Received on 16.11.2020          Modified on 14.01.2021

Accepted on 11.03.2021          ©AJRC All right reserved