Hydrochemical studies and evaluation of groundwater quality of the Quaternary aquifer at Faquss, Al Sharqiya Governorate, Egypt

Abstract

The Quaternary deposits represent the main groundwater aquifer in the study area. During the last few years, the problem of groundwater contamination has been intensified mainly due to natural and human-related factors. The present work aims to study the hydrochemical characteristics and quality assessment of shallow groundwater of the Quaternary aquifer at Faquss district. To achieve that, 16 groundwater samples were collected and analyzed for major ions, trace elements, and microbiological analysis. Constructions of water level map of the Pleistocene aquifer and distribution maps for different ions in groundwater were made by surfer software. Statistical analyses for water quality parameters were carried out. Results indicate that most of the studied area is characterized by fresh water (TDS < 1000 mg/L) with low contents of K, Na, Mg, Ca, SO₄, and Cl reflecting the suitability of ground water for drinking. High contents of TDS, Na, SO₄, and Cl are recorded at the northeastern parts of the area; this refers to the existence of local pollution sources resulting from the infiltration of domestic, agricultural, and industrial wastes in the intensive populated area. The concentrations of trace elements (chromium, copper, cadmium, etc.) in groundwater are within the acceptable limits for drinking and domestic uses. Iron and manganese are over the acceptable limits in most of the area and the groundwater is unsuitable for drinking. Low contents of iron and manganese are recorded at the north, while aluminum contents are over the acceptable limits at the same site. The results of bacteriological analyses indicate the existence of E. coli bacteria in most of shallow wells ranges between 4 and 800 ml. So, shallow groundwater should be chemically treated before drinking. Generally, the groundwater in the studied area is suitable for irrigation, except 19% of wells suffer from sodium hazards. The ratio rNa/rCl varies between 1.012 and 1.56 in most groundwater samples and indicates the continental origin of groundwater in the study area. The ratio r (K + Na)-rCl/rSO₄ reflects either Na₂–SO₄ water type (in 75% of groundwater samples) or NaHCO₃ water type of shallow meteoric origin (in 25% of groundwater samples). The presence of Na₂SO₄ water type in deep meteoric water genesis at shallow depth is associated with sulfate salts (MgSO₄, and CaSO₄) which formed more than 25% of salt combination might reflect the influence of anthropogenic activities. The dominant process determining the water composition is evaporation.

Introduction

Groundwater of the Quaternary aquifer plays a vital role in satisfying water requirements for domestic, agricultural, and industrial purposes. During the last few years, the problem of groundwater contamination has intensified mainly due to natural and human-related factors. Human activities can alter the natural composition of groundwater through the disposal or dissemination of chemicals and microbial matter on the land surface and into soils, or through injection of wastes directly into ground water. Groundwater pollution is defined as an undesirable change in groundwater quality resulting from human activities.

Strong correlations exist between TDS and the major elements, implying that the major elements contribute much to the salinity of groundwater and the tendencies among them follow a similar trend (Qian et al. 2017). Elsewhere, the TDS shows a strong positive correlation with Na⁺, Cl⁻ and SO4²⁻, while the Na⁺ shows a strong positive correlation with SO4²⁻ and Cl⁻ in shallow groundwater samples. The high degree of association between TDS with Na⁺, Cl⁻ and SO4²⁻ indicates the anthropogenic activities; among these are landfill waste sites, septic tanks, domestic and industrial effluents, and intensive use of fertilizers (El Fakharany et al. 2017). Anthropogenic activities have large influence on the relative contributions for the variations of the natural causes and can also introduce the effects of contamination (Satyanarayana et al. 2016). The groundwater in the study area is subject to a potential pollution from the surface due to sources such as: sewer, polluted drains, sewage ponds, septic tanks and refuse disposal sites, and human sources. The values of the BOD and the total suspended solids are very high, exceeding the allowable values, so the primary treatment and biological treatment should be included in the water treatment plants to reduce the concentration in the waste water before it finds its way to the drain and then to the groundwater (Atwa et al. 2015). The NETPATH modeling was utilized to deduce the geochemical evolution of Na-Cl and Na-SO₄ water types along flow path in the Quaternary aquifer system in Belbeis area, east Nile Delta, Egypt. The results indicate that the ion exchange and dissolution are the main processes along flow path with respect to Na-Cl water type. The cation exchange process proceeds by uptaking Ca²⁺ to release more Na⁺ in groundwater. The Na-SO₄ flow path is characterized by the dissolution of dolomite using dedolomitization process, where CaCO³ decreases and Ca²⁺ increases with increasing gypsum saturation index (Shehata and El-Sabrouty 2014).

The most common sources of contamination by trace elements include effluent from mining, industrial wastewater runoff, solid wastes, or waste waters from urban area, agricultural wastes and fertilizers, and fossil fuels (Fostner and Wittman 1981). Trace metals can be toxic and even hazardous to human health even at relatively low concentrations because of their tendency to accumulate in the body. Some studies confirmed that there is a positive correlation between the concentration of trace metal in water and death rate from some cancers. Bioaccumulation of trace metals in the food chain has produced the most well-known metal poisoning. Organisms higher up in the food chain progressively accumulate metals. Eventually, humans at the top of the chain can experience severe health problems (Domenico and Schwartz 1990). The inspection of the chemical analyses of trace elements (Table 1) indicates that most of the trace element concentrations are below the standards limits of drinking water (WHO 2004), except for iron, aluminum, and manganese.

Table 1 Shows the minimum, maximum, and average concentration of the different pollutants

The area under investigation is located in north eastern Nile delta of Egypt, approximately between longitudes 31° 43′, 32° 02′ E and latitudes 30° 36′, 30° 54′ N (Fig. 1). The topography of the northeastern Nile Delta is characterized by low relief, and its surface slopes gently towards the northern direction, while it takes a rolling shape towards the south, where the land rises up to a moderately elevated plateau with elevations that range between 2 and 24 m (above sea level). The climate is hot, dry, and rainless in summer and mild with some showers in winter. It is considered as arid to semi-arid (Zaid 2006) (Fig. 2).

Fig. 1

Location map and groundwater samples of study area

Geology

According to Said and Beheri (1961), Shata (1965), El Fayoumy (1968); Kotb (1988) and Said (1991), the study area is occupied by rock units belonging to the Quaternary sediments. It constitutes variable proportions of sands, clay, and gravels with lateral variation and variable thickness. These sediments rest uncomfortably on the older rock units of the tertiary (Sallouma 1983). The old deltaic deposits (early Pleistocene deposits), which are composed of coarse quartzitic sands and cherty pebbles represent the main groundwater storage unit in the study area. The Quaternary deposits are classified into two rock units; the upper unit is the Holocene Nile silt and clay (flood plain deposits) with sabkha and fine sand deposits, while the lower one is the Pleistocene sand and gravel. Some sand dunes and sand sheets were distributed and belonged to Holocene. The thickness of the Quaternary deposits in the investigated area ranges between 300 and 600 m (Figs. 2, 3).

Fig. 2

Geological map of the location area after Conoco (1987)

Fig. 3

Cross section from south to north (El Fayoumy 1968)

Hydrogeologic setting

Many detailed works have discussed the hydrogeology of east Nile Delta area, among them are: Shata and El Fayoumy 1970; El Shazly et al. 1975; El Diary 1980; Diab et al. (1984), Attia 1985, Korany et al. (1993), Taha et al (1997), Abo El Fadl (2013), Abd AlRahman et al. 2014, Gomaa et al (2014), and Arnous et al (2015).

The study area is mainly occupied by the Quaternary aquifer which is discriminated into two hydrogeological units; the upper unit is the Holocene aquitard and the lower one is the Pleistocene aquifer. The Pleistocene aquifer system consists of sand and gravel with clay lenses: it is covered by a semi pervious Holocene aquitard (clay cap) and rests on an impermeable Pliocene aquiclude. The Quaternary aquifer is unconfined in the Rolling Plains and semi-confined in the rest of the area. The aquifer thickness varies from 300 m in the south to 600 m in the north and northwest. In the Quaternary aquifer the major recharge sources are from irrigation (seepage from canals and subsurface drainage); while discharge takes place through groundwater withdrawals and upward leakage (in the north and depressions). In the major part of the Eastern Nile delta, the fresh groundwater is underlain by saline groundwater (RIGW/IWACO 1990). The groundwater level of the study area ranges from 8 to 3 m (above sea level) (Fig. 4). Groundwater flow in the study area is from southwest to northeast. The transmissivity of the aquifer is considerably high with an average 10,000 m²/day (Attia 1985). The average value of hydraulic conductivity in the eastern portion of Delta is about 100 m/day and the transmissivity reaches 15,000 m²/day (Kotb 1988).

Fig. 4

Water level contour map of the study area after Arnous et al. (2015)

Fig. 5

Salinity content distribution map of the Quaternary aquifer

Materials and methods

To achieve this purpose, field and laboratory measurements were carried. Groundwater samples were collected from 16 shallow open dug wells during August (2016). Electric conductivity and salinity were measured directly in the field. Groundwater samples were collected in one-liter acid washed, well rinsed low density polyethylene bottles and analyzed for chemical parameters using the standard given by the American Public Health Association (APHA 1995). The collected samples were filtered through 0.45 µm membranes. Samples for trace element analysis were acidified with ultrapure HNO₃ to below pH 2. The groundwater samples were analyzed for major ions, trace elements, and microbiological analysis. Besides, constructions of water level map of the Pleistocene aquifer and distribution maps of different contaminants in groundwater by a kriging method are used by surfer software.

The analyzed parameters include the important cations like calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), potassium(K⁺) and anions like bicarbonate (HCO₃), chloride (Cl⁻), sulfate (SO₄), nitrate (NO₃), nitrite (No_2-), and phosphate (PO3⁻⁴). The electrical conductivity (EC) had been measured in the field using EC meter. Calcium (Ca²⁺) and magnesium (Mg²⁺) were determined by titration using standard EDTA. Chloride (Cl⁻) was analyzed by standard AgNO₃ titration, bicarbonate (HCO₃) by titration with HCl, sodium (Na⁺) and potassium (K⁺) was measured by flame photometry, whereas, phosphate, SO₄ and NO₃were measured by spectrophotometer. Total dissolved solids (TDS) were measured by evaporation and calculation methods (Hem 1991). Quality control of analytical data was undertaken by checking ion balances. The ionic charge balance error was within 5%. Trace elements were determined by atomic- absorption instrument.

The quality standards for drinking water have been specified by the World Health Organization (WHO 2004; 2017). The analytical results for the groundwater samples in the study area are presented in the Table 1.

Results and discussion

Drinking suitability

Electrical conductivity (EC)

The most desirable limit of EC in drinking water is prescribed as 1500 µs/cm (WHO 2004, 2017). Elsewhere, the EC of the groundwater is varying from 422 to 2820 µS/cm with an average value of 1194 µS/cm. Higher EC in the study area indicates the enrichment of salts in the groundwater (Table 2).

Total dissolved solids (TDS)

The TDS value of groundwater samples varies between 273 mg/L and 1833 ppm (Table 1). High concentration of TDS in the groundwater is recorded at western and at the northeastern portion of the study area (Fig. 3). According to Hem (1970) based on TDS of groundwater (Table 2), 63% of groundwater samples are fresh (< 1000 mg/L) and lies below the acceptable limits for drinking given by the WHO (2004,2017), while 37% of the samples are classified as brackish and unsuitable for the same purpose. The high concentration of TDS in groundwater is due to leaching of salts from soil and infiltration of domestic sewage into the groundwater.

Table 2 Classification of water salinity according to Hem (1970)

Major ion

The major constituents of dissolved solids in groundwater samples are the following cations: calcium, magnesium, sodium, and potassium and the following anions chloride, sulfate, and bicarbonates. The concentrations of major ions are listed in (Table 1) and their distributions in groundwater are shown on Figs. (5, 6, 7, 8) inclusive.

Fig. 6

Sodium content distribution map of the Quaternary aquifer

Fig. 7

Chloride content distribution map of the Quaternary aquifer

Fig. 8

Sulfate content distribution map of the Quaternary aquifer

The inspection of these figures and Table 1 reveals the following:

• 1. The concentrations of calcium and magnesium ions are below the acceptable limits for drinking.

• 2. The sodium content in groundwater wells varies from 28 to 550 mg/L with an average 166.5 mg/L (Table 1). The areal distribution of sodium content in groundwater wells (Fig. 6) shows that the majority of the area is characterized by low sodium concentrations (< 200 mg/L) and the groundwater is suitable for drinking. High concentrations of sodium (> 200 mg/L) are recorded at western and at the north eastern portion of the investigated area and the groundwater is unsuitable for drinking.

• 3. The chloride content in the study area ranges between 30 and 685 mg/L with an average 200.9 mg/L (Table 1). The areal distribution of chloride content in groundwater wells (Fig. 7) shows that the majority of the area is characterized by low chloride concentrations (< 250 mg/L) and the groundwater is suitable for drinking. High concentrations of chloride (> 250 mg/L) are recorded at the western sector and this area is classified as polluted zones and the water is unsuitable for drinking.

• 4. The sulfate content in groundwater wells varies from 25 ppm to 326 mg/L with an average 112.5 mg/L (Table 1). The areal distribution of sulfate content in groundwater wells (Fig. 8) shows that the majority of the area is characterized by low sulfate concentrations (< 250 mg/L) and the groundwater is suitable for drinking, except at the western zone and at the north-eastern part of the study area, where the sulfate concentrations exceeded the acceptable limit (250 mg/L) and the groundwater is unsuitable for drinking.

The discharge of human, animal, industrial wastes, and irrigation return flows may add substantial quantity of sodium, chloride, and sulfate to groundwater. The remarkable low concentration of salinity and major elements in majority of the study area attributed to the positive hydrochemical impact of the main canal in diluting the groundwater salinity. High concentrations of sulfate and chloride ions (> 250 mg/L) may produce objectionable taste and act as laxative on unacclimated users (Hem 1985; Probe et al. 1999).

Trace elements

Based on the limits presented by WHO (2004), the concentrations of trace elements (chromium, copper, cadmium, etc.) in groundwater are within the acceptable limits for drinking and domestic uses. Iron, manganese, and aluminum contents are over the acceptable limits. Excess amount of absorbed iron is stored primarily in the liver, bone marrow, and spleen resulting in many dangerous diseases (WHO 1984). So, the drinking water must be treated for iron before use. High manganese contents cause stain in laundry and are objectionable in food processing, dyeing, bleaching ice manufacturing, brewing, and certain other industrial processes (Heath 1987).

The concentration of iron in the study area ranges between 0.007 and 0.974 mg/L with an average 0.417 mg/L which is relatively high for drinking. The areal distribution of iron content in groundwater wells (Fig. 9) shows that the majority of the area characterized by high iron concentrations (> 0.2 mg/L) and the groundwater is unsuitable for drinking. Low contents (< 0.2 mg/L) are recorded at the north.

Fig. 9

Iron content distribution map of the Quaternary aquifer

The concentration of aluminum in groundwater of the Quaternary aquifer varies from 0.026 to 0.363 mg/L (Table 1) with an average 0.098 mg/L (Table 1). The areal distribution of aluminum content in groundwater wells (Fig. 10) shows that the majority of the area is characterized by low aluminum concentrations (< 0.2 mg/L) and the groundwater is suitable for drinking. High contents (> 0.2 mg/L) are recorded at the north.

Fig. 10

Aluminum content distribution map of the Quaternary aquifer

The manganese content in the study area ranges between 0.007 to 1.17 mg/L with an average 0.3736 mg/L (Table 1). The areal distribution of manganese content in groundwater wells (Fig. 11) shows that the majority of the area is characterized by high manganese concentrations (> 0.5 mg/L) and the groundwater is unsuitable for drinking. Low contents (< 0.5 mg/L) are recorded at the north. The increase of trace element (Fe, Mn and Al) in groundwater is due to industrial effluent, acid-mine drainage, sewage, and landfill leachate.

Fig. 11

Manganese content distribution map of the Quaternary aquifer

Hydrochemical parameters and water genesis

According to chemical analysis of 16 samples, the ratio rNa/rCl (Sulin 1948; Hounslow 1995) varies between 1.012 and 1.82 in most of the groundwater samples (Table 3) indicating the continental origin of groundwater in the study area. The ratio r (K + Na)-rCl/rSO₄ (Sulin 1948) is more than unity (varies between 1.33 and 4.21) in 25% of the groundwater samples (Table 3) indicating NaHCO₃ water type is of shallow meteoric origin.

Table 3 Hydrochemical parameters and hypothetical salt combinations of water samples

The ratio r (K + Na)-rCl /rSO₄ (Sulin, 1948) is less than unity (varies between 0.13 and 0.97) in 75% of the groundwater samples (Table 3) indicating Na₂SO₄ water type of deep meteoric origin, but the presence of Na₂SO₄ water type at shallow depth reflects the influence of anthropogenic activities.

Hypothetical salt assemblages

Three hypothetical salt assemblages are detected in the groundwater samples (Table 3). These are:

• 1. KCl, NaCl, Na₂SO₄, NaHCO₃, Mg (HCO₃)₂, and Ca (HCO₃)₂

• 2. KCl, NaCl, Na₂SO₄, MgSO₄, CaSO₄ and, Ca (HCO₃)₂

• 3. KCl, NaCl, Na₂SO₄, MgSO₄, Mg (HCO₃)₂, and Ca (HCO₃)₂^.

The study of the percentages of hypothetical salt combinations (Table 3) can be interpreted as follows:

• 1. The first assemblages are detected in 25% of groundwater samples. The presence of NaHCO₃ water type indicates shallow meteoric water origin.

• 2. The second and third assemblages are detected in 75% of groundwater samples (Table 3). The presence of Na₂SO₄ water type reflects deep meteoric water genesis. The presence of Na₂SO₄water type of deep meteoric water genesis at shallow depth is associated with sulfate salts (MgSO₄, and CaSO₄) which forms more than 25% of salt combination and may reflect the influence of human activities.

Hydrochemical classification

Results of analyses (Table 1) are plotted on the Chadha diagram (Fig. 12) to study hydrochemical processes. 50% of the groundwater samples are plotted in domain 7, where alkali metals exceed alkaline earths and strong acidic anions exceed weak acidic anions. The positions of data points in this domain represent Na₂-SO₄²⁻ type; 31.25% of the groundwater samples are plotted in domain 8, where alkali metals exceed alkaline earths and weak acidic anions exceed strong acidic anions. The positions of data points in this region represent NaHCO₃⁻⁻ type waters. 18.75% of the groundwater samples are plotted in domain 5, where alkaline earths and weak acidic anions exceed both alkali metals and strong acidic anions, respectively. The positions of data points in this domain represent Ca⁺², Mg⁺²HCO³⁻ water type.

Fig. 12

Chadha´s diagram for groundwater

The controlling mechanism of water chemistry

The controlling mechanism of the groundwater chemistry can be assessed by plotting hydrochemical data on Gibbs diagram (Gibbs 1970) which suggests that three mechanisms (atmospheric precipitation, rock dominance, and the evaporation-crystallization process) are the major factors controlling the composition of the dissolved salts in the world's waters. Results of analyses (Table 1) are plotted on the Gibbs diagram (Fig. 13) indicating that the dominant process determining the water composition is evaporation. Evaporation of surface water and moisture in the unsaturated zone is the main process in the evolvement of groundwater chemical composition leading to higher salinity.

Fig. 13

Gibbs plot showing major processes controlling groundwater chemistry

Water for irrigation purposes

The quality of water used for irrigation is vital for crop yield, maintenance of soil productivity, and protection of the environment. At the same time, the quality of irrigation water is very much influenced by the land constituents of the water source. SAR, RSC, and Na% were used to determine the suitability of the groundwater for irrigation purposes (Table 1).

The graphic presentation of EC and SAR is important for this purpose. SAR is calculated as follows where all concentrations are given in milliequivalent/liter.

$$ {\text{SAR}} = {\text{Na}}/\sqrt {\frac{{{\text{Ca}} + {\text{Mg}}}}{2}} $$

The salinity laboratory of US Department of agriculture recommends SAR because of its direct relation to adsorption of Na by soil (Richards 1954). The plot of EC and SAR of 16 samples infers that 69% of the samples fall in C2, C3–S1 (Fig. 14) which is generally considered as good for irrigation. About 18.75% of the samples fall in moderate salinity which is considered as permissible for irrigation while, 12.5% of samples dot in very high salinity hazard and is considered unsuitable for irrigation.

Fig. 14

Classification of groundwater samples for irrigation purposes according to U.S. salinity

Sodium percentage

Sodium is an important ion used for the classification of irrigation water due to its reaction with soil, reducing its permeability. Sodium is usually expressed in terms of percent sodium or soluble-sodium percentage (Na%). Percentage of Na + is widely used for assessing the suitability of water for irrigation purposes (Wilcox 1955). The Na% is computed with respect to relative proportion of cations present in water as

$$ {\text{Na}}\% = \left( {\frac{{{\text{Na}} + {\text{K}}}}{{{\text{Ca}} + {\text{Mg}} + {\text{Na}} + {\text{K}}}}} \right) \times 100\% $$

Here, all the concentrations are expressed in meq/l. The values of sodium percent are varying from 25.04 to 78.9% (Table 1) and are less than 200 (maximum allowable limit). Results of calculated Na% (Table 1) are plotted on Wilcox’s diagram (Fig. 15) indicating that 50% samples fall within excellent to good and good to permissible category of irrigation water use. About 31% and 19% samples are classified as permissible to doubtful and doubtful to unsuitable, respectively.

Fig. 15

Wilcox’s classification of groundwater samples of Quaternary aquifer

Residual sodium carbonate (RSC)

The water having excess of carbonate and bicarbonate over the alkaline earth mainly calcium and magnesium, more than allowable limits affects agriculture unfavorably (Eaton 1950; Richards1954). The residual sodium carbonate is computed with the following equation:

$$ {{\rm RSC}} = \left( {{{\rm CO}}_{{{3}}} + {{\rm HCO}}_{{{3}}} } \right) - \left( {{{\rm Ca}}^{{ + {{2}}}} + {{\rm Mg}}^{{ + {{2}}}} } \right) $$

where, all values of cations and anions are expressed in milliequivalents/liter. The residual sodium carbonate is used to distinguish between the different water classes for irrigation purposes. Due to high concentration of Ca and Mg, 81% of groundwater samples have negative values (Table 1), this means that the groundwater is suitable for irrigation purposes while, 19% of the samples have positive values indicating unsuitability for the same purposes.

Microbiological contaminants

The coliform group of bacteria and Escherichia coli are the most frequently used indicators of bacterial contamination but are themselves harmless or nonpathogenic. It is present in large number in the intestines and feces of animals. If E. coli is present, then it is possible that less numerous pathogenic or harmful bacteria which are more difficult to detect are also present. On the other hand, if there is no E. Coli in water sample, then the fecal contamination and of pathogens being present are generally recoded as negligible. The results of bacteriological analyses for shallow groundwater samples (Table 4) indicate that the MPN of E. coli bacteria in most of shallow wells ranges between 4 and 800/ml. So, shallow groundwater should be chemically treated before drinking.

Table 4 Bacteriological analyses of groundwater samples

Conclusions

Chemical and bacteriological analyses of water samples indicate that the shallow groundwater in the studied area are characterized by fresh water (TDS < 1000 ppm) with low contents of K, Na, Mg, Ca, So₄, and Cl and the groundwater is suitable for drinking. High contents of TDS, Na, SO₄, and Clare were recorded at the western parts of the area. This referred to the existence of local pollution sources resulting from the infiltration of domestic, agricultural, and industrial wastes in the intensive populated area. The concentrations of trace elements (chromium, copper, cadmium, etc.) in groundwater are within the acceptable limits for drinking and domestic uses. Iron and manganese are over the acceptable limits in most of the area and the groundwater is unsuitable for drinking. Low contents of iron and manganese are recorded at the north, while aluminum contents are over the acceptable limits at the site. The results of bacteriological analysis indicate the existence of E. coli bacteria in most of shallow wells ranges between 4 and 800 ml. So, shallow groundwater should chemically treated before drinking. Generally, the groundwater in the studied area is suitable for irrigation, except 19% of the wells suffer from sodium hazards.

The water type of groundwater samples varies from Na₂So₄ (in 75% of groundwater samples) and NaHCO₃ water type of shallow meteoric origin (in 25% of groundwater samples). The presence of Na₂SO₄ water type of deep meteoric water genesis at shallow depth associated with sulfate salts (MgSO₄, and CaSO₄) may reflect the influence of anthropogenic activities. The dominant process determining the water composition is evaporation.