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Arab J Geosci (2017) 10:333 DOI 10.1007/s12517-017-3119-5

ORIGINAL PAPER

Assessment of groundwater quality and its suitability for domestic and agricultural uses in Low-Isser plain, Boumedres, Algeria Abdelkader Bouderbala 1

Received: 4 November 2016 / Accepted: 20 July 2017 # Saudi Society for Geosciences 2017

Abstract The assessment of the suitability of groundwater for drinking and irrigation uses was carried out in the alluvial plain of Low-Isser in the north of Algeria. The plain covers an area of 533 km2 and lies in a Mediterranean sub-humid climate. Groundwater is the main source for domestic uses and agricultural activities in this area. Groundwater samples were collected from 15 wells during dry and wet seasons in 2015, and they were analyzed for major cations and anions and compared with drinking and irrigation specification standards. The comparison of chemical concentration with WHO drinking water standards of 2006 shows that more than 30% of groundwater samples are unsuitable for drinking, and the majority of groundwater samples fell on the hard and very hard categories. Suitability of groundwater for drinking was also evaluated based on the water quality index (WQI). It shows more than 80% of samples have good or permissible water quality for dry and wet seasons. In terms of the irrigation usage, generally, groundwater in the study area is suitable for different uses in both seasons according to SAR, %Na, RSBC, and PI. However, water rock exchange processes and groundwater flow have been responsible for the dominated water type Ca–Mg–Cl.

Keywords Drinking water . Irrigation . Alluvial plain . Water quality index . Hydrogeochemistry . Low-Isser aquifer

* Abdelkader Bouderbala [email protected] 1

Department of Earth Sciences, University of Khemis Miliana, Khemis Miliana, Algeria

Introduction Groundwater plays an important role for many purposes as drinking water and irrigation needs, but the quality of this water stays the first factor to evaluate after any uses, because it is a vital process for water management. The deterioration of groundwater quality can be related to the geographical position of the aquifer close to the sea with seawater intrusion or to the situation of the aquifer near to agricultural or industrial activities, and it can be due to the natural processes (Fisher and Mullican 1997; PulidoLeboeuf 2004; El Yaouti et al. 2009; Bouderbala 2015; Ghodbane et al. 2016; Bouderbala et al. 2016). The groundwater chemistry in general depends to the geology of the area, the degree of chemical weathering of rocks, and the interaction between rock and water during the recharge period and groundwater flow directions, and their interaction identifies the groundwater quality and the geochemical properties (Zahid et al. 2008; Gunduz et al. 2010; Brindha and Elango 2012; Kraiem et al. 2014; Bouderbala et al. 2014). Water quality is traditionally evaluated by comparing the values of physicochemical parameters with the standard norms, which provide information only about possible pollutants without giving any specific information on the overall water quality (Houatmia et al. 2016; Chakraborty and Kumar 2016). Water quality index (WQI) is used as an effective tool to express water quality and can be used as an important parameter to assess the water quality very well (Pati et al. 2014; Bouderbala et al. 2016). Other parameters are mostly used for the evaluation of the suitability of water for irrigation, like the sodium adsorption ratio (SAR), residual sodium carbonate (RSC), sodium percentage (% Na), permeability index (PI), and the magnesium hazard (MH). They are usually compared with values given by some authors (Kelly 1940; Richard 1954; Wilcox 1955; Doneen 1964; Raghunath 1987).

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The main objective of this work is to assess the groundwater quality and to determine its suitability for drinking and irrigation purposes in the Low-Isser alluvial aquifer using available ionic data.

– –

Study area – The Low-Isser plain is located approximately at 60 km east of Algiers. It is bounded on the north by the Mediterranean Sea, on the east by Cap Djinet massif, on the south by Kabyle dorsals, and on the west by Djebel Bou-Arous. It lies between latitudes 36.5° to 36.9°N and longitudes 3.5° to 3.8°E. It covers an area of about 533 km2. The plain makes a syncline oriented NE-SW, and the main axis is occupied by the Wadi Isser, which gives the study area its name. The study area is characterized by a Mediterranean subhumid climate with an average annual temperature of about 17.7 °C. The monthly average minimum temperature that occurs in January is 6.3 °C, and the monthly average maximum that occurs in August is 33.8 °C (Period 1980–2014). The most rainfall occurs from October to April (almost 85% of annual rainfall), while the driest months are July and August (less than 20%). The average annual rainfall of the study area for the period 1980–2014 is 740 mm (Baghlia station), so the amplitude of variation of rainfall is very large (between 457 and 1045 mm). From a pedagogical point of view, the study area is formed by the little developed soils that cover more than 70% of the plain with a marked limit of the recent quaternary terrace. The soils are constituted by silts clay, silts, clay and sand, and fine silt texture. The vertisol covers a small area of less than 10%, and it is located in the middle of the southern periphery of the plain, with a moderately heavy structure of the soil. The calcimagnesic soils cover a surface around 12% of the plain, and they are formed by loam and clay and observed near Bordj Menaiel city. The hydromorphic soils cover a small area less than 10%, and they are observed around Isser city. Geology and hydrogeology The region is situated in the Tellian Atlas (or Tell) domain in the north of Algeria. It is formed by steep relief and several coastal plains. The study area is characterized by the presence of Precambrian metamorphic formations. These formations are cut by intrusive or sedimentary rocks (Chemlal 1983). The geological formations that outcrop in the study area from bottom to top are the following (Fig. 1):



The flyschs: they are formed by an alternation of sandstone and limestone with clay and marl, which makes them impermeable. Miocene: it is consisted mainly of clay and marl, with some intercalated levels of conglomerate, limestone, and a friable sandstone. It has a thickness of more than 500 m Pliocene: it is formed essentially by sand, gravel, conglomerate, clay, and blue marl. Quaternary: It shows the existence of seven alluvial terrace deposits, which are stepped and parts fitted together. They are formed essentially by gravel, pebble, sand, and clay. They constitute the main aquifer of groundwater in the plain.

The geophysical study carried out in this plain and the several data of lithological drilling can dress the geometry of the alluvial aquifer. It is a bi-layer aquifer that is formed by pebble, gravel, and sand that is often clayey. The aquifer is approximately 75 m thick. The two aquifers in this plain are connected between them, but not everywhere. The first aquifer has a thickness from 10 to 30 m and is formed by alluvial formations of the recent Quaternary. The second aquifer is about 10 to 45 m thick, formed by alluvial formations of the ancient Quaternary. The aquifer substratum is constituted by blue marl of Piacenzian (Pliocene), and it is reached in some drillings at depth less than 100 m (Fig. 2). Most of the alluvial aquifer recharge comes from the direct infiltration of rainfall into the permeable formations. The aquifer recharge by Wadi Isser is very low in the major part of the plain; this is due to the clogging of banks of this watercourse, and the flow passes through the formations of low permeability (silt and clay). The recharge occurs also by return flow of the irrigation water and the releases from the Beni-Amrane dam at the upstream part of the plain. However, the discharge of the aquifer occurs through pumping abstractions and by outflow toward the sea. The permeability in this aquifer is very low in the upstream of the plain; however, the center and downstream of the plain have moderately high permeability. It varies from 10−4 to 10−3 m/s. The transmissivities of the alluvial aquifer vary between 10−2 and 9.10−4 m2/s (ANRH 2003); this is due to the variation of thickness and the heterogeneity of the aquifer.

Material and methods – –

Eruptive rocks: they are represented by a volcanic rocks, granites, andesites, and labradorite. Crystallophyllian rocks: they are composed mainly by schists, gneisses, and micaschistes. They have low permeability, with a thickness of about 200 m.

Evaluation of groundwater quality for drinking purposes The hydrogeochemistry of the Low-Isser aquifer has been considered in terms of the major ionic elements Ca2+, Mg2+,

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Fig. 1 Geological map of the study area (ANRH 2003, modified)

Na+, K+, Cl−, SO42−, HCO3−, and NO3− and of the physical parameters (pH, EC, and temperature). The physicochemical parameters have been collected from 15 monitoring wells tapping the aquifer in April and September 2015 (Fig. 2). The monitoring wells in this area have depths between 30 and 100 m. They are in the same hydrogeological context and they exploit the alluvial aquifer. They are mainly used for domestic and irrigation supply.

Measurement of electrical conductivity (EC), temperature (T °C), and potential hydrogen (pH) were made immediately in situ by using the universal conductivity meter (WTW Multi340i). While the water samples from wells were taken in 500-mL polyethylene bottles, following the standard guidelines (Schoenleber 2005). The analyses were carried out in the laboratory of the National Agency of Hydraulic Resources according to the norms. Ca2+,

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Fig. 2 Hydrogeological cross-sections in the study area

Mg2+, Na+, K+, SO42−, and HCO3− were determined by atomic absorption spectrometry, chlorides, and nitrates were determined by volumetric and colorimetric methods, respectively. The reliability of all the obtained results was checked using the ionic balance of water, taking the relationship between the total cations and total anions. This shows percentages ranging from − 5 to + 5%, which corresponds to an acceptable reliability for the unit of the chemical results. The total hardness (TH) is considered as an important parameter for assessing water quality for drinking use. It depends on the calcium and magnesium content of water (Raghunath 1987):  TH CaCO3 Þmg=L ¼ 2:497Ca2þ ðmg=lÞ þ 4:1115Mg2þ ðmg=lÞ

In the first step, the relative weights (wi) were assigned to each parameter based on their relative importance in the overall water quality of drinking purposes (Table 1). The maximum weight of 5 has been assigned for parameters like TDS, Na+, Cl−, NO3−, and SO42− due to their importance in water quality assessment, and the minimum weight of 1 has been given to HCO3− because it plays a comparatively less significant role in water quality assessment (Armar and Parmar 2010; Gibrilla et al. 2011; Ravikumar and Somashekar 2012; Bouderbala et al. 2016). In the second step, the relative weights (Rwi) were calculated by using the following equation:

Where the concentrations of Ca2+and Mg2+ are represented in mg/L. The groundwater quality was assessed by comparing the physicochemical parameters of different samples in the study area with drinking water standards recommended by the World Health Organization (WHO 2006). And, the spatial and temporal variations of physicochemical quality parameters of groundwater were analyzed by using the drinking water quality index (WQI) maps of the dry and wet seasons. The calculations of WQI were based on the standards suggested for uses, where 11 water quality parameters were chosen (pH, EC, TDS, Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, and NO3−).

where Rwi is the relative weight, wi is the weight of each parameter, n is the number of parameters. Inthethirdstep,thequalityratingscale(qi)foreachparameterwas attributed by dividing its concentration in each water sample by its respective standard according to the WHO guidelines (WHO 2006):   Ci qi ¼  100 Si where

n

Rwi ¼ wi= ∑ wi i¼1

qi is the quality rating Ci is the concentration of each chemical parameter in each water sample in mg/L Si is the concentration permissible, for each chemical parameter according to the guidelines in mg/L

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Table 1 The weight (wi) and relative weight (Wi) of each chemical parameter Parameters

use in agricultural irrigation. It is used as an index to evaluate the sodicity of soil; it is estimated by the following equation given by Richards (1954):

Drinking water WHO (2006)

Weight (wi)

Relative weight (Wi)

EC (μS/cm)

1500

5

0.119

TDS (mg/l) Cl− (mg/l) SO42− (mg/l) Na+ (mg/l) NO3− (mg/l) Mg2+ (mg/l) Ca2+ (mg/l) HCO3− (mg/l) K+ (mg/l) pH

1000 250 200 150 50 75 100 300 12 8.5

5 5 5 5 5 4 2 2 1 3 Σ wi = 42

0.119 0.119 0.119 0.119 0.119 0.095 0.048 0.048 0.024 0.071 Σ Wi = 1

For computing the WQI, the following equation was used: WQI ¼ ∑Rwi  qi Water quality types were determined based on WQI (Table 2). The spatial distribution maps for values of WQI were prepared using inverse distance weighting (IDW) interpolation technique. Evaluation of groundwater quality for irrigation purposes

Naþ SAR ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Ca2þ þ Mg2þ 2 where the concentrations of Ca 2+ , Mg 2+ and Na + are expressed in meq/L. –

The sodium percentage (Na %) called also soluble sodium percentage (SSP) is an evaluation of percentage of sodium that prevents water irrigation. This parameter needs estimation with the goal to avoid that the soil becoming sodic. Sodic soils present particular challenges because they tend to have a very poor structure which limits or prevents water infiltration and drainage (Ayers and Westcot 1985). It is obtained by using the formula:

%Na ¼ 

ðNaþ þ Kþ Þ x 100  Ca þ Mg2þ þ Naþ þ Kþ 2þ

where the concentrations of Ca2+, Mg2+, Na+, and K+ are expressed in meq/L. –

The residual sodium bi-carbonate (RSBC) index of irrigation water or soil water is used to indicate the alkalinity hazard for soil. The RSBC index is used to find the suitability of the water for irrigation in clay soils which have high cation exchange capacity. When dissolved sodium relative to dissolved calcium and magnesium has an important concentration in water, clay soil swells or undergoes dispersion which drastically reduces its infiltration capacity. It is calculated by the following equation (Ayers and Westcot 1985; Raghunath 1987):   RSBC ¼ ðHCO3− þ CO3− Þ− Ca2þ þ Mg2þ

The suitability of groundwater for irrigation purpose was evaluated by using the basic criteria, in the goal to assess if there is a negative impact on crop growth and on the soil structure (Bouderbala 2015). Salinity and indices such as sodium absorption ratio (SAR), sodium percentage (Na %), residual sodium bi-carbonate (RSBC), and permeability index (PI) are very important parameters for determining the suitability of groundwater for agricultural uses. They were calculated for each sample and the ions are expressed in meq/l.

where the concentrations of HCO3–, CO3–, Ca2+, and Mg2+ are expressed in meq/L.





The sodium adsorption ratio (SAR) is a parameter used to assess the irrigation water quality and its suitability for the

Table 2 Classes proposed for drinking water quality based on water quality index (WQI) (Chatterjee and Raziuddin 2002) Class

1 2 3 4 5

Range of WQI for drinking purposes

Type of water quality

< 25 25.1–50 50.1–75 75.1–100 > 100.1

Excellent water quality Good water quality Permissible water quality Doubtful quality Water unsuitable for drinking uses

The permeability index is calculated employing the following equation (Raghunath 1987): pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Naþ þ HCO3−   100 PI ¼  2þ Ca þ Mg2þ þ Naþ where the concentrations are expressed in meq/L. Hydrogeochemical evaluation To better understand the hydrogeochemical processes that take place in this alluvial aquifer, the analyses of samples were plotted on the Piper trilinear diagram, in the goal to determine the

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Fig. 3 Potentiometric map of the alluvial aquifer of Low-Isser (in meters) and location of wells (April 2015)

Table 3 Chemical analysis of groundwater of Low-Isser aquifer (Dry and wet seasons 2015)

Parameter

pH TDS (mg/l) EC (μS/cm) TH (mg/l) Na+ (mg/l) Ca2+(mg/l) Mg2+ (mg/l) K+ (mg/l) Cl− (mg/l) SO42− (mg/l) HCO3− (mg/l) NO3− (mg/l) % Na SAR RSBC PI

Dry season

Wet season

Max.

Min.

Average

SD

Max.

Min.

Average

SD

8.3 958.9 1913 672 128 154 75 9 259 229 555 20 45.0 2.1 − 2.7 60.0

7.1 582.7 1150 319 45 62 35 2 82 63 138 4 16.4 0.6 − 7.7 35.8

7.6 729 1445.9 463.1 98.4 101.8 50.9 3.7 198.4 125.5 285.5 10 32.8 1.5 − 4.6 47.8

0.4 106.6 209.1 116.9 22.3 28.3 12.2 2.3 45.9 48.3 134.3 4.8 9.1 0.4 1.2 7.8

8.3 965.6 1925 759.3 123 184 73 8 248 247 615 23 53.2 2.1 − 1.5 71.2

7.1 431.6 850 169.6 24 30 23 2 66 27 107 4 10.9 0.3 − 7.0 32.0

7.6 648.3 1280.4 430.7 80.8 94.0 47.7 3.1 175.0 97.9 286.1 9.1 31.5 1.3 − 3.9 48.5

0.4 166.9 334.6 173.4 23.8 47.1 14.5 1.7 47.6 63.9 155.9 6.7 12.8 0.5 1.8 12.3

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different water types in this aquifer. Groundwater is represented as a solution of cationic constituents (Ca2+, Mg2+, and alkaline metals), anionic constituents (SO42−, Cl−), and constituents contributing to alkalinity (carbonate (CO32−) and HCO3−). The groundwater types were determined based on the hydrochemical facies concept by combining cation and anion fields (Piper 1953).

Table 5 Classification of groundwater quality based on TDS (Davis and De Wiest 1966) TDS (mg/l) Water category

Percent in Percent in dry season wet season

< 500 500–1000 1000–3000 > 3000

– 100 – –

Desirable for drinking Permissible for drinking Useful for irrigation Unfit for drinking and irrigation

– 100 – –

Results and discussion Potentiometric map The groundwater levels in the wet season compared to the dry season in 2015 show a net increase of static levels during wet season compared to dry season; this is due to the recharge of the aquifer by rainfall during winter and spring. The potentiometric maps of wet and dry seasons in 2015 show the same morphology of the potentiometric surface. We present in this work only one map (potentiometric map of the dry season, Fig. 3). This map indicates groundwater flow from the borders toward the center of the plain, with a main direction of flow from South to North. This groundwater flow coincides with the main axis of the plain with a final outlet being the Mediterranean Sea. It coincides approximately with the path of Wadi-Isser which drains the surface waters. The average hydraulic gradient downstream is 0.05% (isopotentiometric curves are spaced), due to the high thickness and good permeability of the aquifer in this sector. However, in the center of the plain (near to Bordj Menaeil city), the hydraulic gradient is higher than 0.50% (iso-potentiometric curves are tightened); this is due to the low permeability, low thickness of the aquifer, and the bedrock slope. This aquifer is mainly recharged by rainfall infiltrations at outcrops of alluvial terraces, where the aquifer is unconfined; it is also recharged by water influx from the border formations located in the two parts of the plain. Evaluation of groundwater quality for drinking and irrigation purposes Understanding the groundwater quality is important, because it is the major factor which decides its suitability for different Table 4 EC

Classification of groundwater quality for drinking based on

EC (μS/cm)

Water category

Percent in dry season

Percent in wet season

< 750 750–1500 1500–3000 > 3000

Desirable for drinking Permissible for drinking Bed quality for drinking Hazardous for drinking

– 66.67 33.33 –

– 73.33 26.67 –

uses as domestic, industrial, and agricultural purposes. Table 3 summarizes statistical results of the various physical and chemical parameters such as maximum, minimum, average, and standard deviation of analyzing groundwater samples from the study area. Results were compared with standard guideline values recommended by the World Health Organization (WHO 2006). The pH values range from 7.1 to 8.3 for the both periods with averages 7.7 and 7.6 on dry and wet seasons, respectively. The highest values (pH = 8.3) for both periods were recorded in the middle and upstream of the plain near to Wadi Isser; they confirm that groundwater is slightly alkaline. During the dry season, the average of electrical conductivity (EC) is 1445.9 μS/cm, while in the wet season, it is 1280 μS/cm. It suggests that more than 33 and 26% of water samples are exceeding the standard recommend by WHO (2006) of 1500 μS/cm in dry and wet seasons, respectively (Table 4). The EC is related to the concentrations of ions capable of carrying an electrical current. The highest values were observed in the center of the plain between the cities of Borj-Menaiel and Isser; it is due probably to anthropological pollution and dissolution of minerals. The total dissolved solids (TDSs) represent the total concentration of dissolved substances in water. They were varied from 958.9 to 582.7 mg/l and from 965.6 to 431.6 mg/l for dry and wet seasons, respectively (Table 5). This indicates that the groundwater in this aquifer is acceptable for drinking (Davis and De Wiest 1966). However, the presence of high levels of TDS in water may be distasteful to consumers owing to the Table 6 Sawyer and McCarty’s classification of groundwater quality based on the total hardness Total hardness as CaCO3 (mg/l)

Water category

Percent in dry season

Percent in wet season

0–50 50–100 100–150 150–200 200–300 > 300

Soft Moderately soft Slightly hard Moderately Hard Hard Very hard

– –

– –



6.67 20 73.33

100

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Fig. 4 Spatial distribution of water quality index. a Wet season. b Dry season 2015

a

b

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resulting taste and to excessive scaling in water pipes, heaters, boilers, and household appliances. Water with extremely low concentrations of TDS may also be unsuitable to consumers due to its insipid taste; it is also often corrosive to watersupply systems (WHO 2006). The moderately higher values of TDS may be due probably to lithology of the aquifer, anthropological pollution, or leaching of salts from soil above certain anthropogenic activities (Deutsch and Siegel 1997; Sethy et al. 2016). The values of TDS obtained from almost all the groundwater samples collected in this study are within the range of freshwater type. Hardness in water is caused by the presence of high levels of calcium (Ca2+) and magnesium (Mg2+) ions. They are the most abundant in groundwater. Total hardness (TH) in the study area is varied from 319 to 672 mg/l and an average of 463 mg/l in the dry season and from 169 to 759 mg/l and an average of 430 mg/l in the wet season (Table 6). A generalized classification of groundwater based on the value of TH (Sawyer and McCarty 1967) shows that the majority of groundwater samples falls in the category of very hard water in dry season; however, in wet season, only 20% of the total groundwater samples are hard and the rest (73.33%) has a very hard water quality. This is due to the increase of the concentrations of major ions, which can cause health effects (Sethy et al. 2016). Concerning the major ions, the concentrations of sodium, magnesium, potassium, and nitrates in this area are below the maximum limit recommended by WHO (2006). The chloride concentrations show only one sample in the dry season exceeds the limit of WHO (200 mg/l). It is noteworthy that the evolution of chloride contents is done in the direction of groundwater flow and in the center of the plain. This is due to the evaporation of the

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Sodium (%) Water class Percent in dry season Percent in wet season < 20 20–40 40–60 60–80 > 300

Excellent Good Permissible Doubtful Unsuitable

13.33 53.33 33.34 – –

20.00 40.00 40.00 – –

shallow waters of the aquifer which leads to a progressive enrichment of chloride in the direction of groundwater flow. We can explain the high values in the center of the plain by discharge of untreated wastewater. These pollution sources can produce local groundwater contamination. The sulfate concentrations of groundwater in this aquifer for both seasons show only one sample exceeds the standard recommended by WHO (200 mg/l). It is located in the center of the plain, between the cities of Borj-Menaiel and Isser; it is due probably to the use of some fertilizers in agriculture or the discharge of untreated wastewater. The high levels of sulfates above the normal limit can cause a problem on the health of people, particularly gastrointestinal problems. The calcium concentrations show nearly 40% of samples in both seasons exceed the maximum limit recommended by WHO (100 mg/l). It is due to the exchange between water and carbonate rocks (limestone and dolomite). The concentrations of bicarbonate are ranged between 138 and 55 mg/l for dry season and from 107 to 615 mg/l for wet season. Bicarbonate is responsible for the alkalinity of groundwater. They are probably derived from weathering of silicate rocks, dissolution of carbonate precipitates, atmospheric and soil CO2 gas (Kumar et al. 2012). The quality of groundwater of Low-Isser aquifer for drinking purpose was evaluated through the WQI. The relative weight, quality rating, and subindex for each parameter were calculated, and the WQI at the monitoring wells for the dry and wet seasons was determined. The WQI values were then interpolated using the IDW method in a GIS environment to obtain the WQI map (Chatterjee and Raziuddin 2002; Jasmin and Mallikarjuna 2014). The WQI ranged from 38 to 82 during the wet season and from 44 to 82 during the dry season (Fig. 4a, b). The WQI map Table 8 RSBC

Fig. 5 US Salinity diagram for classification of irrigation waters in LowIsser aquifer (Richards 1954)

Sodium percent and water classes

Groundwater quality based on residual sodium bi-carbonate

RSBC (Meq/l))

Water category

Percent in dry season

Percent in wet season

< 1.25 1.25–2.5 > 2.5

Good Doubtful Unsuitable

100 – –

100 – –

333 Table 9 1964)

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Page 10 of 13 Groundwater quality based on permeability index PI (Doneen

PI

Water class

Percent in dry season

Percent in wet season

< 25 25–75 > 75

Good Suitable Unsuitable

– 100 –

– 100 –

reveals that the aquifer possessed for wet and dry seasons, respectively, good water quality for drinking 40 and 6.67% of samples, permissible water quality 46.67 and 80%, doubtful and poor category 13.33% for both periods. It may be due to leaching of ions, overexploitation of groundwater, agricultural impact, and direct wastewater discharge of effluents. The high percentage of good water quality during wet against dry season may be due to the groundwater recharge during the winter and spring seasons. The evaluation of groundwater quality for irrigation purposes in the study area based on salinity hazard shows that the majority of the samples were acceptable for irrigation purposes (EC < 2250 μS/cm). All the samples in both seasons are falling under medium salinity classes indicating that the water is of permissible quality. The classification of groundwater samples with respect to SAR during wet and dry seasons shows that the SAR value of all the samples are found to be less than 10 (Fig. 5) and are classified as excellent water for irrigation. On the basis of US Salinity Laboratory hazard diagram (Richards 1954) plotted by

Table 10

Groundwater characterization on the basis of Piper diagram

Subdivision of facies

Water type

Percent in dry season

Percent in wet season

I II III IV

Ca2+–Mg2+–Cl−–SO42− Na+–K+–Cl−–SO42− Na+–K+–HCO3− Ca2+–Mg2+–HCO3−

86.67 – – 13.33

66.66 6.67 – 26.67

correlating the sodium absorption ratio and electrical conductivity, all the groundwater samples of the study area fall in the category of C3S1 groups both in dry and wet seasons (100%). This class indicates high salinity and low alkalinity. The classification of groundwater quality based on the percent sodium (% Na) is shown in Table 7. The values vary from 16 to 45%, which indicate all of the samples having an excellent to permissible water quality for irrigation. According to the classification of groundwater based on RSBC values in the study area, they are having values less than 1.25 and they are ranged from − 7.7 to − 2.7, which show that Ca2+ and Mg2+ ions are in excess than bicarbonates (Table 6). The groundwater samples show that all the samples belong to good category (Table 8) and are suitable for irrigation purposes. The classification of groundwater based on the permeability index (Table 9) shows values ranging between 25 and 75 for both seasons, and all samples belong to suitable category for irrigation.

(I) Ca2+ - Mg2+ - Cl- - SO42- type ; (II) Na+ - K+ - Cl- - SO42- type; (III) Na+ - K+ - HCO3- type; (IV) Ca2+ - Mg2+ - HCO3- type Fig. 6 Chemical facies of groundwater according to Piper diagram. a Dry season. b Wet season 2015

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obviously, the water–rock interactions are still in progress and also could be due to the cation exchange processes. The second group belongs to a small number of samples. The water type of samples is Ca–Mg–HCO3 indicating 13.33 and 26.67% for the dry and wet seasons, respectively, which could be considered as freshwater (recharge water), younger than the groundwater of the first group. The chemical composition of water varies in time and space due to the natural recharge and flow patterns and due to chemical processes between the water and rocks. If magnesium, calcium, bicarbonate, and sulfate are derived from simple dissolution of calcite, or dolomite, then a charge balance should exist between the cations and anions (Jalali 2005). As described in Fig. 7, the relationship between (Ca2+ + Mg2+) and (HCO3− + SO42−) was employed to identify this water–rock interaction. It shows all of samples (100%) fall above the equiline in the wet season, reflecting the effect of carbonate and sulfate mineral dissolution (Yidana et al. 2008; Yidana and Yidana 2010; Yu et al. 2012), while in dry season, more than 93% of samples fall below the equiline, indicating the influence of silicate dissolution and ion exchange. The hydrochemical diagram proposed by Chadha (1999) was also used to better understand the hydrochemical process of groundwater in the alluvial plain of Low-Isser. This diagram has been successfully applied in several studies around the world to identify the different hydrogeochemical processes (Karmegam et al. 2011; Thilagavathi et al. 2012). The hydrochemical processes proposed by Chadha (1999) can classify water into four major groups:

Ca2+ + Mg2+ (meq/l) 14 12

Excess of Ca2+ and Mg2+ 10 8 6

Wet season Dry season

4 2

Excess of HCO3- and SO42-

0 0

2

4

6

8

10 HCO3- +SO42- (meq/l)

Fig. 7 Relationship (Ca2+ + Mg2+) vs (SO42− + HCO3−) in groundwater

Hydrogeochemical facies The evolution of the hydrogeochemical parameters of groundwater is examined by plotting the concentrations of major ions on Piper Diagram (Piper 1953). The concept of hydrochemical facies was developed in order to identify the water composition in different classes. They revealdifferenttypesofwatersin thestudy area (Fig. 6a, b), which are identified and listed in Table 10. It clearly explains the variation or domination of cation and anion concentrations during wet and dry seasons. Groundwater samples are classified into two major groups. The first group belong the highest percentage 86.67 and 66.67% of samples during dry and wet seasons, respectively. The dominant groundwater type is Ca–Mg–Cl–SO4. The water samples belonging in this group are explained by a wide transitional step from fresh recharge water to mixed water type; Fig. 8 Groundwater samples plotted on Chadha’s diagram for dry and wet seasons 2015

& &

Group 1: represents recharge water type, Ca-HCO3 Group 2: water with an excess of Ca–Mg–Cl and with ionexchanged reverse Group 3: characterize saline water rich in Na–Cl, which are either seawater or having stayed in contact with salt formations at few times

&

(Ca2+ + Mg2+8) + (Na+ + K+)

Wet season

6

Dry season

Group 4

Group 1

4 2

(HCO3-) + (SO42-+ Cl-) -12

-10

-8

-6

0 -4

-2

0

2

4

6

8

10

-2

Group 3

-4 -6

-8

Group 2

12

333

&

Page 12 of 13

Group 4: water ion-exchange Na–HCO3

Applying this diagram on the groundwater of plain, it shows that the majority of samples are classified in group 2, and few samples fall in group 1. Group 1 contains the water samples located near to Isser and Si Mustpha cities, in the upstream of the plain, in the recharge area. This group of samples has calcium and bicarbonate water type. Group 2 is characterized by excess of Ca2+ and Mg2+ compared to Na+ and K+; it is due to the alteration of minerals rich in Ca2+-like carbonate rocks, and probably due also to the exchange between water and rock, along the groundwater flow (Fig. 8). This group has Ca–Mg–Cl-SO4 water type.

Conclusion The groundwater quality in the Low-Isser plain has been assessed by using physicochemical parameters. The dominate water type in this aquifer is chloride calcique (more than 66 and 86% for wet and dry seasons, respectively) and might be due to the geology of the area and water-rich ionic exchange, and the groundwater samples fell in the hard to very hard category for the majority of wells. The computation of WQI for 15 samples distributed over the study area ranged from 32 to 82 in wet and dry seasons. The results of WQI for drinking show that the groundwater of this aquifer indicates a permissible water quality for more than 46.67 and 80% of samples and a good water quality for more than 40 and 6.67% of samples, in wet and dry seasons, respectively. The high values of WQI in this plain are mainly due to the higher values of chlorides, sulfates, nitrates, bicarbonates, calcium, and sodium. It may be due to leaching of ions, overexploitation of groundwater, agricultural impact, and direct wastewater discharge of effluents. The results, based on EC, Cl, SAR, RSBC, % Na, and PI, indicate that the groundwater quality of this aquifer varies from good to permissible for irrigation purposes. Groundwater of this aquifer can be safely used for irrigation without sodium hazard to soils or negative impacts on the yields of crops and properties of soils. However, agricultural practices should be managed very well to ensure a safe use of the water resource for a sustainable development of the agriculture in this area.

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