Hydrochemical evaluation of spring's water in Mila Wilaya, North-East Algeria

Groundwater provides an estimated 25–40% of all the world's drinking water. It can interact with the different minerals in the aquifer and become enriched in several elements, some of which are good for health, others less so and some of which can even be toxic if critical concentrations are exceeded (Ferreira et al. 2017). Geological processes are the main influences on water chemistry, due to infiltration and circulation in deeper layers, water changes its chemical composition while interacting with different geological layers (Jasik et al. 2020).

Springs result from a concentration of groundwater flow paths, so that water flows out of a single location (or a small number of nearby locations) rather than diffusely into surface watercourses. As such, spring water chemistry reflects the interaction of groundwater with the host rock of the aquifer as well as any chemical constituents that may be introduced from surface sources. Spring water chemistry is therefore not intrinsically different from groundwater chemistry and the same principles apply (White 2010).

The quality of spring waters depends not only on natural factors such as aquifer lithology, groundwater velocity, recharge water quality and interaction with other types of water or aquifers, but also on anthropogenic activities, which can alter these fragile systems, either by polluting them or by changing the hydrological cycle (Helena et al. 2000).

In Mila Wilaya, there are 415 springs identified with a mobilized flow of 11,633,315 m³/year (Soukehal & Cherrad 2011). In the rural areas of Mila, springs are the most important source of water for the people living in this region. They are found almost everywhere and play a vital role in the life of the inhabitants. Most of the Communes are located in hilly and isolated areas, where spring water has been used to satisfy domestic needs (washing, drinking), livestock watering and irrigation of agricultural fields by the villagers of these Communes.

The main objective of this article is to determine the hydrochemical waters properties of 25 springs, located in the Mila region, to evaluate their drinkability, and understand the composition and origin of the chemical elements that make up the mineral content of these waters, as well as, how they are acquired?

The hydrochemical properties of these waters springs samples were analysed during the year 2021 at the ADE laboratory of Mila (Algerian Water Company).

The hydrographic network is extremely dense and hierarchical, the shape of the region as a basin with an East-West corridor shows a general orientation of the hydrographic network South-North or North-South depending on the case (Mebarki 1982).

Mila is located at the limit between two geological provinces, and seems to present a less important seismicity than the neighbouring regions such as the Constantine or Babors area. It belongs to the Tellian domain, the eastern segment of the Maghrebid chain, which represents the alpine chain of North Africa. This chain, made up of aquifers put in place during the Miocene, was structured by the Alpine Orogen, their base could be dated to the terminal Burdigalian and their top to the Quaternary (Zouaoui 2008; Chettah 2009).

The formations in the Mila region are primarily transgression deposits from the continental and marine realms (Mio-Pliocene detrital and evaporite deposits). One of the geological characteristics of the Mila basin is the predominance of clay deposits leading to numerous ground instabilities. The crushing zones of the major tectonic accidents generally constitute favourable zones for the infiltration, circulation and storage of water. Indeed, these zones constitute good aquifers and often show spring resurgence (Athmania et al. 2010). The 25 springs studied are located in the northern communes of Mila Wilaya (Figure 1).

The methods described by Rodier (Rodier et al. 2009) were followed during field and laboratory work. The goal was to ensure that the water samples truly represented the hydrochemical properties and conditions of their natural environment.

Water was taken directly from the springs, where electrical conductivity (EC), salinity (SAL), TDS (with a Hach multiparameter, sensION156) and pH (Adwa, AD 1000) were measured on-site. Other elements are measured in the laboratory, such as turbidity (Hach, 2100N). Concentrations of potassium (K⁺), sodium (Na⁺) and calcium (Ca²⁺) were analysed using a flame photometer (JENWAY, PFP7), while those of nitrate (⁠⁠), nitrite (⁠⁠) and total hardness (TH) were titrated using the volumetric method; sulphate (⁠⁠), magnesium (Mg²⁺) and chlorine (Cl⁻) by spectrophotometry (Hach, LANGE, DR3900). Samples were analysed for the main cations and anions used for chemical characterization.

The application of graphical methods to raw data enables results to be visualized, compared and interpreted more quickly and easily. The graph of total dissolved solids (TDS) versus TH (in Excel) enables samples to be positioned within their water quality ranges. The Piper diagram enables the facies of each sample to be determined (created by Diagram V6.77) based on its anion and cation composition. The role of the Gibbs diagram (in Excel) is to visualize the origin of certain chemical elements present in the analysed water. The graphical representation of the Ca/Mg ratio (in Excel) shows the origin of calcium, as a function of its content in the water.

The use of statistical analysis of major ions (Mg²⁺, Na⁺, K⁺, Ca²⁺, ⁠, and Cl⁻) as a basic tool to interpret the hydrogeochemical characteristics of groundwater (Gao et al. 2019). Table 1 presents the statistical description of the main ions in Mila spring waters.

Table 1

Descriptive statistics of the main parameters of Mila spring's water, 2021

Statistics .	Unit .	Average .	Max .	Min .	Standard deviation .
EC	μS/cm	517.18	1,808.00	78.70	291.60
TDS	mg/l	255.98	904.00	45.00	199.20
Sal	%	0.23	0.90	0.00	0.21
Turb	NTU	4.70	36.00	0.62	7.66
TH	mg/l	223.52	800.00	52.00	154.88
Ca2+	mg/l	53.38	272.54	4.01	53.64
Mg2+	mg/l	23.19	55.89	4.84	12.67
Na+	mg/l	14.12	50.00	8.00	9.13
K+	mg/l	1.2	7.00	0.00	1.58
	mg/l	190.87	378.20	9.76	113.89
Cl−	mg/l	38.80	193.00	12.76	48.46
	mg/l	31.55	121.33	0.70	30.99
	mg/l	5.71	20.42	0.00	7.06
	mg/l	0.03	0.10	0.00	0.03
OM (Organic matter)	mg/l	1.11	2.33	0.00	0.61
DR (dry residue)	mg/l	333.92	1,314.00	4.00	279.95

Statistics .	Unit .	Average .	Max .	Min .	Standard deviation .
EC	μS/cm	517.18	1,808.00	78.70	291.60
TDS	mg/l	255.98	904.00	45.00	199.20
Sal	%	0.23	0.90	0.00	0.21
Turb	NTU	4.70	36.00	0.62	7.66
TH	mg/l	223.52	800.00	52.00	154.88
Ca2+	mg/l	53.38	272.54	4.01	53.64
Mg2+	mg/l	23.19	55.89	4.84	12.67
Na+	mg/l	14.12	50.00	8.00	9.13
K+	mg/l	1.2	7.00	0.00	1.58
	mg/l	190.87	378.20	9.76	113.89
Cl−	mg/l	38.80	193.00	12.76	48.46
	mg/l	31.55	121.33	0.70	30.99
	mg/l	5.71	20.42	0.00	7.06
	mg/l	0.03	0.10	0.00	0.03
OM (Organic matter)	mg/l	1.11	2.33	0.00	0.61
DR (dry residue)	mg/l	333.92	1,314.00	4.00	279.95

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Dissolution of carbonates is an important origin of Ca²⁺ and Mg²⁺; the dominant cation present in the collected water samples is Ca²⁺. The concentration of Ca²⁺ varies from 4.01 to 272.54 mg/l. the increase in Ca²⁺ concentration in the samples is caused by the dissolution of gypsum and limestone, this ion may also be due to cation exchange (Li et al. 2016). Mg²⁺ ranges from 4.84 to 55.89 mg/l. The average values of Na⁺ concentrations vary from 8 to 50 mg/l, with a maximum concentration of Na⁺ observed at the level of the El Dehamecha 2 spring, in the Commune of Sidi Khlifa (south of the study area). The average concentration of cations in the spring waters are observed as follows: Ca²⁺ > Mg²⁺ > Na⁺ > K⁺.

The dominant anion in the spring water samples is ⁠, with average concentrations in the following order: > Cl⁻ > > ⁠. varies between 9.76 and 378.20 mg/l in, with an average of 190.87 mg/l. The average concentrations of Cl⁻ and are 38.8 and 31.55 mg/l, respectively. Anthropogenic inputs, such as industrial and agricultural activities, are a major source of in groundwater (Kabour 2017). The concentration of in the study area found varies from 0 to 20.42 mg/l.

The Piper diagram is considered one of the simplest and widely used methods for determining groundwater facies (Gao et al. 2019). In this study, the Piper diagram is obtained using ‘Diagram v 6.77’ software.

It can be noted that most of the samples taken from Mila springs are considered to be of freshwater type. The bicarbonate concentration in the majority of these springs is in the range that reflects the calcareous origin, except for the springs in the South, which reflect the Cl⁻––Ca²⁺ type (Houima, Ayoun soltane and Ain Kahla). The results show that a high concentration of Mg²⁺ generally accompanies a high concentration of Ca²⁺, which may be an indication of dolomitization, especially for these sources. Low concentrations of Mg²⁺ reflect the carbonate origin.

Table 2 gives the thresholds set by Algerian regulations for spring water (JORADP 2000, 2011; Hazzab 2011; Kabour 2017) and the standards of drinkability according to the WHO (Word Health Organization) regulations (W.H.O. 2017). Referring to these standards, we note that all sampled sources are within Algerian and WHO standards, except for Tikerzalet (0.347 mg/l) and Maaret (0.486 mg/l), which slightly exceed the iron concentration threshold. The Houima and Ouled Belkhir springs have a concentration of 272.54 mg/l in Ca²⁺ and 55.89 mg/l Mg²⁺ respectively resulting from the dissolution of the carbonate formations of Jebel Msid Aicha. These concentrations slightly exceeds both standards. The three springs are located in the north of the study area.

Table 2

Comparison of water quality indicators for Mila springs, 2021

Features .	Symbol .	Unit .	Maximum permissible value according to the standards .		Mila sources maximum concentration .
			Algerian (JORADP 2000, 2011) .	WHO (W.H.O. 2017) .
Electrical conductivity	EC	μS/cm	2,800	2,000	1,808
Chlorides	Cl−	mg/l	200–500	250	193
Sulphates			400	250	121.33
Calcium	Ca2+		75–200	100	272.54
Magnesium	Mg2+		150	50	55.89
Sodium	Na+		200	150	50
Potassium	K+		20	12	7
Nitrates			50	50	20.42
Nitrites			0.1	3	0.1
Iron	Fe		0.3	0.3	0.486

Features .	Symbol .	Unit .	Maximum permissible value according to the standards .		Mila sources maximum concentration .
			Algerian (JORADP 2000, 2011) .	WHO (W.H.O. 2017) .
Electrical conductivity	EC	μS/cm	2,800	2,000	1,808
Chlorides	Cl−	mg/l	200–500	250	193
Sulphates			400	250	121.33
Calcium	Ca2+		75–200	100	272.54
Magnesium	Mg2+		150	50	55.89
Sodium	Na+		200	150	50
Potassium	K+		20	12	7
Nitrates			50	50	20.42
Nitrites			0.1	3	0.1
Iron	Fe		0.3	0.3	0.486

Values that exceed the maximum permitted are shown in bold.

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The molar ratio Ca²⁺/Mg²⁺ gives information on the origin of these elements from the dissolution of calcite and dolomite. If this ratio Ca²⁺/Mg²⁺ ≤ 1, it is a dissolution of dolomite, on the other hand, a higher ratio >1 indicates the dissolution of calcite (Mayo & Loucks 1995), when it is higher than 2, it indicates the dissolution of silicate minerals (Katz et al. 1997; Nair et al. 2015).

Na⁺ and Cl⁻ are two chemical elements present in natural waters and are often linked to the dissolution of halite (NaCl). The evolution of Na⁺ is studied as a function of the chloride content, because chloride is considered to be a stable and conservative tracer of evaporites, very soluble, rarely entering into saline precipitations, not involved in redox phenomena and little influenced by the intervention of bacteria. In addition, its movement is not delayed in water (Ouandaogo-Yameogo et al. 2013; Kabour 2017).

The exchange with the rock matrix also controls the calcium content in the spring waters of the Mila region, in case the residence time is relatively long.

There is a decrease in the calcium content in relation to + ⁠, and a decrease in Na+ in relation to Cl⁻, which implies a high content of and ⁠, which is frequently found in the solution of evaporite sedimentary rocks, particularly gypsum (CaSO₄).

The projection of the different points on the Ca²⁺/(⁠ + ⁠) – Na⁺/Cl⁻ diagram (Figure 9) shows that 24% of the water points undergo a base exchange with a long residence time. 64% of the points present the natural state and 12% express an excess of Ca²⁺ compared to and ions, probably due to the gypsum formations, which provide more Ca²⁺ ions than can be consumed by the effect of chemical precipitation or the effect of calcium fixation by the clays (Debieche 2002).

This work presents the hydrogeochemical characteristics of the waters of 25 springs located in the region of Mila, as well as the evaluation of their suitability for drinking and domestic use. This characterization allowed to determine the order of classification of the concentrations of the main cations in these waters, which is Ca²⁺ > Mg²⁺ > Na⁺ > K⁺, while for the anions, it is: > Cl⁻ > > ⁠.

Referring to the graph of TDS versus TH, most of the water samples belong to the fresh–fresh and soft–moderately hard water domain, and the dominant water types are of mixed type.

Rock leaching and precipitation inputs are the predominant processes in the formation of hydrochemical components. The dissolution of silicate, calcite, dolomite and gypsum are the main processes that contribute to define the chemistry of Mila's spring waters; there is also another important hydrogeochemical process that contributes to the elaboration of this quality, which is the exchange of cations, such as Ca²⁺ and Mg²⁺ with Na⁺ and K⁺.

According to Algerian and WHO standards, the quality of spring water in the Mila region is of excellent class for most of the samples analysed.

In order to preserve and protect the quality of these springs against the accelerating process of urbanization and industrialization, it is necessary to establish a strategy of control, surveillance and reinforcement of the monitoring of the physicochemical quality, in order to achieve a sustainable development and management that respects the environment and allows the rational use of spring water.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.