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Article

Hydraulic and Hydrogeochemical Characterization of Carbonate Aquifers in Arid Regions: A Case from the Western Desert, Egypt

by
Mahmoud M. Khalil
1,*,
Mostafa Mahmoud
1,
Dimitrios E. Alexakis
2,*,
Dimitra E. Gamvroula
2,
Emad Youssef
3,
Esam El-Sayed
1,
Mohamed H. Farag
4,
Mohamed Ahmed
5,
Peiyue Li
6,
Ahmed Ali
1 and
Esam Ismail
1
1
Geology Department, Faculty of Science, Minia University, Al-Minya 61519, Egypt
2
Laboratory of Geoenvironmental Science and Environmental Quality Assurance, Department of Civil Engineering, School of Engineering, University of West Attica, 250 Thivon & P. Ralli Str., GR12241 Athens, Greece
3
Groundwater Sector, Ministry of Water Resources and Irrigation, Cairo 3855402, Egypt
4
Exploration Department, Egyptian Petroleum Research Institute, Cairo 11727, Egypt
5
Geology and Geophysics Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
6
School of Water and Environment, Chang’an University, No.126 Yanta Road, Xi’an 710054, China
*
Authors to whom correspondence should be addressed.
Water 2024, 16(18), 2610; https://doi.org/10.3390/w16182610
Submission received: 12 July 2024 / Revised: 30 August 2024 / Accepted: 9 September 2024 / Published: 14 September 2024
Browse Figures
Versions Notes

Abstract

:
Using geochemical and pumping test data from 80 groundwater wells, the chemical, hydrologic, and hydraulic properties of the fractured Eocene carbonate aquifer located west of the Al-Minya district, the Western Desert, Egypt, have been characterized and determined to guarantee sustainable management of groundwater resources under large-scale desert reclamation projects. The hydrochemical data show that groundwater from the fractured Eocene carbonate aquifer has a high concentration of Na+ and Cl− and varies in salinity from 2176 to 2912 mg/L (brackish water). Water–rock interaction and ion exchange processes are the most dominant processes controlling groundwater composition. The carbonate aquifer exists under confined to semi-confined conditions, and the depth to groundwater increases eastward. From the potentiometric head data, deep-seated faults are the suggested pathways for gas-rich water ascending from the deep Nubian aquifer system into the overlying shallow carbonate aquifer. This mechanism enhances the dissolution and karstification of carbonate rocks, especially in the vicinity of faulted sites, and is supported by the significant loss of mud circulation during well drilling operations. The average estimated hydraulic parameters, based on the analysis of step-drawdown, long-duration pumping and recovery tests, indicate that the Eocene carbonate aquifer has a wide range of transmissivity (T) that is between 336.39 and 389,309.28 m2/d (average: 18,405.21 m2/d), hydraulic conductivity (K) between 1.31 and 1420.84 m/d (average: 70.29 m/d), and specific capacity (Sc) between 44.4 and 17,376.24 m2/d (average: 45.24 m2/d). On the other hand, the performance characteristics of drilled wells show that well efficiency ranges between 0.47 and 97.08%, and well losses range between 2.92 and 99.53%. In addition to variations in carbonate aquifer thickness and clay/shale content, the existence of strong karstification features, i.e., fissures, fractures or caverns, and solution cavities, in the Eocene carbonate aquifer are responsible for variability in the K and T values. The observed high well losses might be related to turbulent flow within and adjacent to the wells drilled in conductive fracture zones. The current approach can be further used to enhance local aquifer models and improve strategies for identifying the most productive zones in similar aquifer systems.

1. Introduction

Carbonate rocks, such as limestones and dolomites, provide a variety of natural resources to humans, including different karst landscapes, building and industrial materials, thermal baths, geothermal energy sources, drinking water resources from fractured and karstic aquifers, and the promise of possibilities for carbon dioxide (CO2) sequestration [1,2]. Aquifers composed of carbonate rocks, particularly limestones, are among the most productive aquifers worldwide due to their unique hydraulic properties, i.e., solution-enhanced flow paths and high transmissivity [3]. Globally, carbonate rock aquifers cover approximately 15% of the Earth’s surface and are the sources of groundwater for 10 to 25% of the world’s population [4,5,6,7,8]. In the Middle East and North Africa (MENA), which are both affected by low rainfall and limited surface water resources, extensive carbonate rocks/potential karst aquifers are widely distributed, with Iran having the most significant area share (54.3%), followed by Egypt (45.2%) [2]. The latter exploits groundwater from Upper Cretaceous to Middle Miocene fissured and karstified limestones spanning across different Egyptian geographic settings—the Eastern Desert, the Western Desert, and the Sinai Peninsula—with thicknesses ranging from 200 to 1000 m, as well as abundant water reserves of up to 5 billion m3 (Figure 1) [9,10,11]. While the majority of these aquifers are located in the middle and northern parts of the Western Desert, their wells are few and mostly concentrated on the Nile Valley’s east and west desert fringes (Figure 1). During the last few years, many wells have been drilled and groundwater exploitation from different aquifers in the Western Desert has increased under the policy of horizontal expansion, which includes the reclamation of about 1.5 million acres (approximately 630,000 hectares) (Figure 1) [12]. A large portion of the 1.5 million acres is allocated to the west Al-Minya reclamation project (Figure 1), which involves over 700,000 acres (294,000 hectares) and is heavily dependent on the groundwater from carbonate aquifers.
The expanded use of groundwater resources for intensive agriculture and irrigation purposes requires careful hydrogeochemical and hydrogeological assessment in order to manage groundwater sustainability and protect this resource from degradation [13,14]. This is especially important when dealing with exploited carbonate aquifers, which vary widely in terms of their hydraulic and hydrochemical properties [3,15,16] due to different pathways for water flow, continuous water–rock interaction, and the relatively fast dissolution and precipitation kinetics of carbonate minerals [17,18]. Furthermore, anthropogenic contamination from agricultural effluents and wastewater could quickly infiltrate fractured carbonate strata and affect a large aquifer area [16,19]. By analyzing the chemical composition of groundwater, such as its major and minor ions, it is possible to identify the water’s origin, age, and quality, as well as the geochemical processes controlling the flow and chemistry within the aquifer [20,21]. In addition, pumping tests could be used to estimate various hydraulic properties of the aquifer, such as its transmissivity, hydraulic conductivity, and storage capacity [20,22,23,24]. These properties are essential for understanding how water moves through the aquifer and how it responds to changes in pumping or recharge rates [20,24]. Hydrochemistry and pumping tests can help develop effective management strategies for the sustainable use and protection of groundwater resources.
The hydrochemical, aquifer flow dynamics, and hydraulic parameters approaches were applied for the first time to characterize the Eocene carbonate aquifer in the west of the Al-Minya district using the data obtained from the new wells drilled in the area. The main goals of the current study are to provide valuable information about the aquifer’s hydraulic parameters, the groundwater’s geochemistry, and the groundwater flow to help with the groundwater sustainability in such an intensively irrigated agricultural area. The achieved results should be examined periodically to assess the influence of the human impact on groundwater quality and reserves.

1.1. Study Area

The study area is located in the west of the Al-Minya governorate in the Western Desert of Egypt (Figure 1). The area’s topography is characterized by a relatively flat to gently undulating sandy and gravelly plain, with elevations ranging from 100 to 150 m. The area has an arid to hyper-arid climate with hot summers and mild winters. The average annual precipitation is between 0 and 5 mm/year, while the average yearly potential evapotranspiration rate is 1610 mm/year [25].
Water 16 02610 g001
Figure 1. A location map of Egypt showing the distribution of carbonate rocks/potential karst aquifers.
Figure 1. A location map of Egypt showing the distribution of carbonate rocks/potential karst aquifers.
Water 16 02610 g001

1.2. Geological and Hydrogeological Setting

Tertiary and Quaternary formations are the main geologic units in the study area, as indicated by the surface geologic map [26] and subsurface geologic data of 80 drilled wells (Figure 2a). Quaternary sediments overlie the Tertiary rocks, i.e., Eocene, and include playa and gravel deposits exposed at the eastern part of the study area (Figure 2a). Tertiary deposits are mainly represented by the surface Qatarani Formation (Oligocene–Pleistocene) and subsurface Eocene carbonate rocks [25,27,28,29]. The Qatarani Formation deposits cover most of the study area and are composed of gravel, sand, and limestone fragments with clay intercalations. They increase in thickness southeastward from the drilled wells, reaching 400 m thickness at well no. 60. Eocene carbonate rocks include, from bottom to top, the Minia (Lower Eocene) and Samalut (Middle Eocene) formations. The Minia Formation is composed of dolomitic limestone, while the Samalut Formation is composed of massive, cavernous, and fractured limestone, as well as chalky limestone with clay and marl intercalations [28,29]. According to the lithologic logs of the drilled wells, the thickness of the Eocene rocks increases towards the east and the north, becoming more than 400 m thick. Structural analysis of the surface, from the geologic map, and deep-seated faults, from the correlating lithologic logs of drilled wells, has highlighted the predominance of NW-SE (Gulf of Suez) and NE-SE (Gulf of Aqaba) trends in the study area (Figure 2b–d).
The Eocene carbonate rocks of the Samalut and Minia formations represent the main aquifer unit in the study area. Low-permeability confining units of clay mostly bind the carbonate aquifer system from above, making it a confined aquifer (Figure 3). The high loss of mud circulation during drilling operations highlights the predominance of fissures, fractures or caverns, and solution cavities in the Eocene carbonate aquifer. This feature is also recorded for carbonate aquifers located east of the Nile Valley [11]. Based on the data from 80 drilled wells, the depth to groundwater varies from 70.85 m (at well no. 22) to 104.56 m (at well no. 71), increasing eastward. From the potentiometric map (Figure 4), water moves outward in all directions from local potentiometric highs in the central and southwestern parts of the study area. The static water level decreases toward the southwest from 39.25 m.a.s.l. (at well no. 21) to 30.40 m.a.s.l. (at well no. 29). Depressions on the potentiometric map, located southwestward, mark major withdrawal centers in the study area.

2. Methodology

2.1. Water Sampling and Analysis

Groundwater geochemistry was investigated by sampling and analyzing 80 wells in the study area (Table 1; see Figure 2b for sample locations). Water samples were taken in duplicate, filtered using a 0.45 µm Millipore filter, and stored in 50 mL polyethylene bottles at 4 °C. For cation analysis, one bottle of each sample was acidified using a few drops of ultra-pure HNO3 to reduce pH < 2 and prevent heavy metal adsorption to the walls of the containers. Temperature, pH, and total dissolved solids (TDS) were measured in situ using portable ADWA AD111 and AD330 m (Table 1). Alkalinity, as HCO3− concentration, was determined by titration using a sulfuric acid solution and methyl orange as indicators. Chemical analyses were performed at the Central Laboratory for Environmental Quality Monitoring, the National Water Research Center (NWRC), Egypt. Anions (Cl−, SO42−) were analyzed using ion chromatography (Dionex DX120), whereas cations (Ca2+, Mg2+, Na+, K+) were measured using inductively coupled plasma mass spectrometry (ICP-MS). The ionic balance error for major ion analysis did not exceed ±5%.

2.2. Aquifer (Pumping) Test

Step-drawdown, long (constant-rate) pumping, and recovery tests were done for all 80 wells in the study area. Pumping and recovery tests were conducted as a single well (pumped well) test. A step-drawdown test was conducted for 16 h and consisted of four increasing pumping rates (duration/step = 4 h). On the other hand, the constant-rate test was run for 24 h at a pumping rate of 200 m3/h (880 gpm). While conducting the pumping test, the dynamic groundwater head was measured in the pumping well itself at selected intervals, ranging from 5 min to 24 h at the beginning and end, respectively, as well as the time from the moment pumping stopped until the full recovery of the static water head (Table S1 in the Supplementary Materials). The depths of the production, i.e., the pumped wells, ranged from 420 m (at well no. 2) to 750 m (at well no. 80). The diameter of the production wells was considered as 339.7 mm, with the housing pipe set at a diameter of 178 mm. Submersible pumps of 125 HP and 8 inches in diameter were used for testing. The discharge pipe was equipped with a standard flow meter, and an electric sounder continuously monitored water levels in the pumped well. The results of the step-drawdown, constant-rate, and recovery tests were analyzed graphically, as shown in Figure 5, by using Rorabaugh’s method [30], Jacob’s straight-line method [31], and Theis’s recovery methods [32], respectively. From the step-drawdown analysis, well performance criteria, such as well loss and well efficiency, were derived from the relationship between the drawdown (S) and the discharge rate (Q) expressed by the following equation [33]:
S = BQ + CQ2
where S is the drawdown in the pumped well (m), B is the aquifer loss coefficient (h/m2), and C is the well loss coefficient (h2/m5). The coefficients B and C are usually obtained graphically by plotting S/Q as a function of Q for each step (Figure 5a), assuming equal duration, obtaining B as the intercept of the resulting line with the S/Q axis and C as its slope [34].
On the other hand, the well efficiency (Weff) was also calculated with the following equation:
Weff (%) = BQ/(BQ + CQ2) × 100
where BQ is the aquifer loss, CQ2 is the turbulent head loss, and (BQ + CQ2) is the total head loss. Values of well efficiency ≥ 70% are considered acceptable [35] and indicate a properly designed and developed well.
The well development factor is the ratio of well loss to formation loss multiplied by 100 and calculated as (C/B)*100. In accordance with [34], a well development factor of <0.1 indicates “very effective” development, “effective” development is between 0.1 and 0.5, “fairly effective” development is between 0.5 and 1, and “poorly effective” development is above 1.
The specific capacity (Sc), defined as the quantity of groundwater produced in a well per unit of drawdown, is derived from Equation (1), according to the following:
Sc = Q/S = 1/(B + CQ2).
For straight-line methods (Cooper–Jacob and Theis recovery), best-fit trend lines were drawn on graph outputs (Figure 5b,c), and the slope and related parameters were estimated from the graphs. The formulas listed below were then used to calculate transmissivity (T) and hydraulic conductivity (K) for the pumping well.
T = 2.303Q/4π∆S
K = T/b
where Q is the constant discharge rate (m3/day), ΔS is the drawdown difference per one log cycle of time, and b is the saturated aquifer thickness in meters (compiled from geophysical logging and during drilling activities).

3. Results and Discussion

3.1. Groundwater Flow Dynamics

It can be observed from the potentiometric map (Figure 4) that the groundwater flow radiates in all directions from the central and southwestern local potentiometric highs, i.e., the groundwater recharge areas. Since the area is barren, mainly desert, and not fully cultivated, it cannot relate the local recharge highs to enhanced recharge or infiltration from surface agricultural activities. The alternative explanation is, therefore, the artesian upwelling of groundwater from deep aquifers, i.e., the Nubian sandstone aquifer system, to shallow carbonate aquifers through vertical/subvertical faults, as reported from different locations across the Western Desert [35,36]. The correlation between the locations of local potentiometric highs and delineated surfaces and deep-seated faults provides evidence for this mechanism (Figure 3 and Figure 4). Also, based on the Nubian well records from the surrounding areas, the deep Nubian aquifer is separated from the overlying carbonate aquifer by Paleocene shales and has high groundwater heads which facilitate groundwater discharge from the deep to shallow horizons [25,36,37].

3.2. Geochemistry of Groundwater

The chemical compositions of groundwater samples from the Eocene carbonate aquifer are listed in Table 1. The pH ranges from 7.1 to 7.83 (neutral to slightly alkaline water), with an average of 7.5. The alkaline nature of the groundwater contributes to the stability of carbonate minerals in the aquifer. The total dissolved solids (TDS) show an increasing trend from the central and western parts toward the southeast and southwest parts of the study area, which is consistent with the direction of groundwater flow and explains the correlation between recharge/discharge and the chemistry of the groundwater in the Eocene carbonate aquifer (Figure 4). They vary between 2176 and 2912 mg/L, with an average of 2358 mg/L. A box plot shows the wide range of concentrations of the major dissolved components, with high concentrations of Cl− (729 to 1109 mg/L, with an average of 865 mg/L) and Na+ (415.5 to 810 mg/L, with an average of 537 mg/L) and low concentrations of Mg2+ (17.4 mg/L to 64.6 mg/L, with an average of 38.5 mg/L) and K+ (14.8 to 28 mg/L, with an average of 23 mg/L) (Figure 6a). Considering the Piper triangular diagram, all the groundwater samples are plotted as Na+ − Cl− water type (Figure 6b).

3.3. Main Hydrochemical Processes

Ion ratio plots were developed to identify the main processes controlling the groundwater composition of the Eocene carbonate aquifer (e.g., [11,38,39]). Most groundwater samples (77%) represented in the (Ca2+ + Mg2+) vs. (HCO3− + SO42−) diagram fall above the 1:1 ratio, indicating a predominance of carbonate (calcite, dolomite, and aragonite) and/or evaporite (gypsum and anhydrite) weathering (Figure 7a). On the other hand, 23% of the samples were plotted below the 1:1 ratio, suggesting additional processes in the aquifer, i.e., dissolution/precipitation and/or ion exchange. Groundwater derived from the dissolution of calcite or dolomite is plotted on an equivalent ratio of 1:2 or 1:4, respectively, in the Ca2+-HCO3− scatter diagram [40,41,42]. In the Ca2+ vs. HCO3− diagram (Figure 7b), the majority of groundwater samples (>90%) are far deviated from the 1:1, 1:2, and 1:4 ratios and have excess Ca2+, suggesting other sources of Ca2+. Evaporite and silicate weathering could be possible sources of Ca2+ in the groundwater of the Eocene carbonate aquifer. The lack of equimolar correlation between Ca2+ and SO42− suggests that the dissolution of evaporites (anhydrite and/or gypsum) is not the primary process resulting in Ca2+ excess (Figure 7c). The absence of dolomite in the Eocene carbonate mineralogy is proposed to be the main cause of the low content of Mg2+ in the groundwater. The Na+ + K+ vs. total cations (TZ+) plots indicate silicate weathering where the samples fall along the Na+ + K+ = 0.5 TZ+ and/or Na+ + K+ = 0.33 TZ+ lines [43,44,45,46,47]. The bivariate plot of (Na+ + K+) vs. TZ+ (Figure 7d) shows sample points from the Eocene carbonate aquifer falling below and away from the Na+ + K+ = 0.33 TZ+ and Na+ + K+ = 0.5 TZ+ lines, indicating the absence or low contribution of silicate weathering. This is also well supported by the dominance of Cl− over Na+ in the bivariate plot of Na+ versus Cl− (Figure 7e). The Na+ − Cl− plot also shows high correlation (r2 = 0.85) and most samples fall along the 1:1 line, suggesting the halite dissolution source of Na+ and Cl− ions in groundwater (Figure 7e). Depletion of Na+ (Figure 7e) and enrichment of (Ca2+ + Mg2+) over (HCO3− + SO42−) (Figure 7a) indicate that the ion exchange reactions also contribute to groundwater mineralization [48,49]. The ion exchange reactions are evident from the plot of (Ca2+ + Mg2+) − (SO42− + HCO3−) vs. (Na+ + K+) − Cl− (Figure 7f), which shows a straight line with a slope of −0.91, an intercept of 0.63, and a strong correlation of 0.95, revealing the dominance of ion exchange processes, i.e., ion exchange and reverse ion exchange reactions, in the groundwater aquifer in the study area.

3.4. Aquifer Hydraulic Parameters

Using the drawdown data plotted on a semi-logarithmic graph (Figure 5), the groundwater aquifer hydraulic parameter values, in the form of specific capacity (Sc), transmissivity (T), and hydraulic conductivity (K), could be determined using Equations (3)–(5). The Sc, T, and K values are shown in Table 2 and Figure 8.
The specific capacity (Sc) ranges from 1.85 m2/h (44.4 m2/d) at well no. 75 to 724.01 m2/h (17,376.24 m2/d) at well no. 68. Based on Sen’s Sc classification (1995), the drilled wells were categorized into high-production wells (41%; more than 18 m2/h), located in the middle and northeast of the study area (Figure 8a), and medium-production ones (59%; from 1.8 to 18 m2/h). The variation in the Sc values might be related to each wells’ design, pumping discharge rate, and consistency of pumping rate [50,51]. High-production wells, e.g., nos. 22, 27, 36, 43, 49, and 68, were observed to have low drawdown water level values (from 0.3 to 2.38 m; Table S1) and, hence, lower pumping costs.
The estimated T values, from the Cooper–Jacob method, varied from 552.77 m2/d at well no. 67 to 604,197.19 m2/d at well no. 22, with an average of 26,390.26 m2/d (Figure 8b and Table 2). On the other hand, the T estimates from the Theis recovery method ranged from 57.32 m2/d at well no. 60 to 174,421.37 m2/d at well no. 22, with an average of 10,776.49 m2/d (Table 2). The estimated K, using the Cooper–Jacob method, ranged from 1.41 m/d at well no. 67 to 2205.1 m/d at well no. 22 (Figure 8c), with an overall average of 101.77 m/d. The K values acquired using Theis’s recovery method varied from 0.13 m/d at well no. 60 to 636.57 m/d at well no. 22, averaging 40.15 m/d (Table 2). The wide variations in the K and, subsequently, T values are related to fracture/permeable zones due to the karstification process associated with rapid changes in the high density of fractures and joints, particularly surrounding or near the recorded faults shown in Figure 2 and Figure 3. Furthermore, the variations in carbonate aquifer thickness and clay/shale content in different locations (Figure 3) are responsible for the observed variations in the K and T values. The spatial distribution map of K and T shows that the values are found to be high at three localized areas located in the center and northwestern portions of the study area (Figure 8b,c), close to local recharge highs identified in Figure 4 and explained to be formed as a result of artesian upwelling of groundwater from deep aquifers of the Nubian aquifer system, through deep-seated vertical faults. The deep and gas-rich waters ascending from the Nubian aquifer along faults enhance the dissolution of overlying carbonate rocks, leading to strong karstification that produces abundant collapse features, resulting in high T and K values [25,52]. Based on Gheorghe [53], the carbonate aquifer is classified as a moderate (50 to 500 m2/d)- to high-potential aquifer (T > 500 m2/d, as shown in Table 2).

3.5. Groundwater Well Performance Assessment

The present estimation of well performance criteria, including well loss coefficient, aquifer loss coefficient, and well efficiency, is based on the analyzed results of the step-drawdown test for 80 wells (Supplementary Materials, Table S1). The well loss coefficient ranges from 5.17 × 10−6 h2/m5 at well no. 68 to 2.41 × 10−3 h2/m5 at well no. 75, while the aquifer loss coefficient varies from 6.76 × 10−5 h/m2 at well no. 19 to 2.28 × 10−1 h/m2 at well no. 61. The average well efficiency of all steps for each well varies from 0.47% (well no. 28) to 97.08% (well no. 61), with an average of about 33.8%. In this regard, the efficiency values of 10 wells range from very good to excellent (more than 70%), while 12 wells have moderate efficiency values (50 to 70%), and most wells (58 wells) are inefficient, with less than 50% efficiency. This is also confirmed by the well development factor, which classifies 51 wells as poorly effective (well development factor > 1) and 12 wells as fairly effective (ranging from 0.5 to 1). The well loss percentages vary from 2.92% (well no. 61) to 99.53% (well no. 28). The higher well loss percentages in most wells might be related to turbulent flow within and adjacent to the wells in fractured carbonate aquifers with high conductive fracture zones. Other factors might be attributed to partial penetration of the well in the aquifer, heterogeneity in hydraulic characteristics, the clogging of well screens, and/or improperly positioned pumps [51,54].

4. Conclusions

Nearly half of Egypt’s territory is underlain by Upper Cretaceous to Middle Miocene carbonate rocks, which host extensive shallow karstified and fractured aquifers that promote irrigated agriculture under large-scale development programs to reclaim the barren desert. However, there is a scarcity of site-specific data available to adequately characterize the chemical, hydrologic, and hydraulic properties of a karst-dominated aquifer to allow the effective management of groundwater resources. Based on hydrochemical data, groundwater in the study area is characterized by a high Na+ − Cl− composition, with salinities ranging from 2176 to 2912 mg/L (brackish water). Various ionic ratio scatter plots indicate that the water–rock interaction and the cation exchange process are the major geochemical mechanisms controlling the groundwater composition. The carbonate aquifer exists under semi-confined conditions. The aquifer has a trend of increasing T and K toward the southwest portion of the study area. The wide range of T and K values can be attributed to fractures and permeable zones due to karstification caused by rapid changes in fracture and joint density, particularly surrounding or near deep-seated faults, where ascending gas-rich water from the deep Nubian aquifer enhances the dissolution of overlying carbonate rocks, leading to strong karstification. Based on the results of step-drawdown tests, the performance characteristics of the drilled wells show that well efficiency ranged between 0.47 and 97.08% and well losses ranged between 2.92 and 99.53%. Turbulent flow within and adjacent to the wells drilled into high conductive fracture zones might also cause the observed high well losses. Finally, continuous observation and evaluation of the aquifer’s hydraulic parameters and groundwater geochemistry are recommended to monitor and control the anthropogenic influence on the aquifer’s performance.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w16182610/s1, Table S1: Well and formation characteristics obtained from step-drawdown tests for 80 wells of the fractured carbonate aquifer.

Author Contributions

Conceptualization, M.M.K., E.E.-S., M.H.F., M.A. and E.I.; methodology, M.M.K., M.M., E.Y., E.E.-S. and E.I.; software, M.M.K.; validation, M.M.K., M.M., E.Y., E.E.-S. and P.L.; formal analysis, M.M.K.; investigation, M.M. and E.I.; data curation, M.M.K., M.M., E.Y., M.H.F., M.A. and E.I.; writing—original draft preparation, M.A.; writing—review and editing, M.M.K., M.M., D.E.A., D.E.G., E.Y., E.E.-S., M.H.F., P.L., E.I. and A.A.; visualization, M.M.K., E.E.-S., M.H.F., P.L. and E.I.; supervision, M.M.K. and E.I.; project administration, M.M.K. and E.I.; funding acquisition, M.A. All authors have read and agreed to the published version of the manuscript.

Funding

This work is funded by the Researchers Supporting Project (number RSP2024R455), King Saud University, Riyadh, Saudi Arabia.

Data Availability Statement

This article has no associated data, and all the data used in this study are present in the article.

Acknowledgments

The authors acknowledge the fund by the Researchers Supporting Project (number RSP2024R455), King Saud University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare no conflicts of interest.

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Water 16 02610 g002
Figure 2. (a) A geologic map of the west Al-Minya reclamation project, the Western Desert, Egypt. (b) A location map of 80 wells drilled in the fractured Eocene carbonate aquifer. The two insets show (c) the structural trends of surface faults, in the blue rose diagram in the upper right corner, and (d) deep-seated faults, in the red rose diagram in the lower right corner.
Figure 2. (a) A geologic map of the west Al-Minya reclamation project, the Western Desert, Egypt. (b) A location map of 80 wells drilled in the fractured Eocene carbonate aquifer. The two insets show (c) the structural trends of surface faults, in the blue rose diagram in the upper right corner, and (d) deep-seated faults, in the red rose diagram in the lower right corner.
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Figure 3. Hydrogeologic cross sections along the study area. See Figure 2b for the cross-section location.
Figure 3. Hydrogeologic cross sections along the study area. See Figure 2b for the cross-section location.
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Figure 4. A potentiometric head map of the fractured Eocene carbonate aquifer in the study area.
Figure 4. A potentiometric head map of the fractured Eocene carbonate aquifer in the study area.
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Figure 5. Examples of (a) step-drawdown pumping test for well no. 4, (b) long duration or constant-rate pumping test for well no. 22, (c) recovery pumping test for well no.14.
Figure 5. Examples of (a) step-drawdown pumping test for well no. 4, (b) long duration or constant-rate pumping test for well no. 22, (c) recovery pumping test for well no.14.
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Figure 6. (a) A box plot showing the variation of the major ions in the groundwater of the fractured Eocene carbonate aquifer, and (b) a Piper diagram of 30 groundwater samples from the fractured Eocene carbonate aquifer.
Figure 6. (a) A box plot showing the variation of the major ions in the groundwater of the fractured Eocene carbonate aquifer, and (b) a Piper diagram of 30 groundwater samples from the fractured Eocene carbonate aquifer.
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Figure 7. Binary plots of (a) (Ca2+ + Mg2+) vs. (HCO3− + SO42−), (b) Ca2+ vs. HCO3−, (c) Ca2+ vs. SO42−, (d) Na+ + K+ vs. total cations (TZ+), (e) Na+ vs. Cl−, and (f) (Ca2+ + Mg2+) − (SO42− + HCO3−) vs. (Na+ + K+) − Cl−.
Figure 7. Binary plots of (a) (Ca2+ + Mg2+) vs. (HCO3− + SO42−), (b) Ca2+ vs. HCO3−, (c) Ca2+ vs. SO42−, (d) Na+ + K+ vs. total cations (TZ+), (e) Na+ vs. Cl−, and (f) (Ca2+ + Mg2+) − (SO42− + HCO3−) vs. (Na+ + K+) − Cl−.
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Figure 8. A spatial distribution map of the (a) specific capacity (Sc), (b) transmissivity (T), and (c) hydraulic conductivity (K) of groundwater wells in the fractured Eocene carbonate aquifer.
Figure 8. A spatial distribution map of the (a) specific capacity (Sc), (b) transmissivity (T), and (c) hydraulic conductivity (K) of groundwater wells in the fractured Eocene carbonate aquifer.
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Table 1. The physical parameters and major chemical composition of the groundwater from the Eocene carbonate aquifer.
Table 1. The physical parameters and major chemical composition of the groundwater from the Eocene carbonate aquifer.
Well IDWell Depth (m)pHT (°C)TDS (mg/L)Cations (mg/L)Anions (mg/L)
Ca2+Mg2+Na+K+HCO3−Cl−SO42−
17507.7334.82387.215347.3508.528288901186
35667.7235.72342135.5557.74494.522254875.75185.55
55507.7333.72310.4153.0247.3508.528288901186
156007.131247197.6317.4160222249843.53231.71
215507.6832.8227217948.89510.521302834.27298.06
234507.2736.42316.8148.458.2539.524195908355
245007.236.4243217418.29810192581109403.07
256007.2236.12278.4152.738.05678.5222261007364
275007.2631.52355.286.4527.7674.523278959.01201.71
286007.2533.623689927.89648.522288916.88233.68
296007.1635.8291215717.9786.5202571104.9373.23
314507.26342470.48828649.523289917235
346007.71312182.4199.3737.81438.527288794261
364507.79312304151.5740.92464.525276753245
374507.59322368140.4835.66532.524246868221
385007.6432.52176144.3645.31469.524298759258
404507.7631.82304179.9736.14436.525293773228
416307.76322284.8171.9434.4449.524295748219
454507.6233.42470.4143.7640550.525258879229
475007.432.72304169.4664.34449.524385.4749249
515507.45352355140.3537.08537.525236895.5215
524507.54342412.8141.3433.89518.521222884193
535007.6432.92265.6133.1330.71509.516.1207.4871.8171
594507.7534.22272149.9853.95415.522284729239
605107.7135.52400170.1845.39444.526234807261
637007.5435.52355145.5635.71481.524224833200
655007.5334.12176134.733.8512.521233860195
724507.334.42342.4164.350.27439.524304.9730296
737507.8334.22310.4117.0934.2539.524213853.5214.1
807507.6731.32541154.3830.26513.514.8224.5890.6180
Table 2. The Sc, T, and K values from the step-drawdown test, constant-rate test, and recovery test.
Table 2. The Sc, T, and K values from the step-drawdown test, constant-rate test, and recovery test.
Well No.Step-Drawdown TestCooper–Jacob MethodTheis Recovery Method
Specific Capacity (Sc)
200 m3/h		T
200 m3/h		bKT
200 m3/h		K
m2/hm2/dmm/dm2/dm/d
14.692376.75225.0010.562131.559.47
2106.5317,360.00184.4594.1223,430.25127.03
315.1130,951.70166.60185.784919.9929.53
43.70772.68148.755.19503.343.38
515.561501.11160.119.38596.203.72
610.091019.77160.656.35583.443.63
712.081288.94178.507.221703.459.54
83.423920.08404.009.70639.191.58
97.64791.90347.002.28544.501.57
107.95763.17243.893.13595.812.44
11103.4624,249.52286.0084.79984.573.44
1210.79567.90207.552.74206.971.00
137.433589.77196.0218.31410.262.09
147.78791.86280.002.8393,149.52332.68
155.572023.82270.007.501026.653.80
1697.1515,432.45237.2065.0616,046.7767.65
1720.981985.00249.487.96411.501.65
184.241736.28377.004.61530.951.41
19114.28318,048.84213.841487.322606.9112.19
206.19590.72219.412.69142.060.65
216.90681.38335.002.03317.020.95
22312.41604,197.19274.002205.10174,421.38636.57
235.451842.12213.488.63385.691.81
2419.08986.82212.784.64714.663.36
257.36874.94385.002.27135.920.35
269.991555.65292.505.321890.666.46
27180.591414.49282.505.01NANA
287.891091.18390.002.80NANA
2911.931211.35375.003.23182.650.49
306.112449.73260.009.421010.623.89
3114.991094.93235.004.66277.251.18
3211.361677.33308.365.4488.490.29
3319.6950,251.72300.00167.5110,819.0736.06
344.556234.41335.0018.61341.421.02
3534.8211,803.76350.0033.733177.319.08
36219.4130,799.44275.00112.006700.2324.36
3762.854192.24280.0014.971065.613.81
385.192685.75337.007.97344.871.02
3914.651431.46290.004.9455,349.72190.86
4037.743468.78318.0010.91677.272.13
4148.872226.90290.007.6810,492.1236.18
4290.4018,100.14240.0075.422186.119.11
4389.4669,438.74280.00248.0048,963.21174.87
4420.895683.23260.0021.8621,699.6083.46
456.121125.92247.004.56175.470.71
4618.556584.71298.0022.109547.8332.04
4750.99181,863.35302.00602.207192.3423.82
4875.05109,118.01305.00357.761979.856.49
4992.1953,275.08280.00190.27166,049.15593.03
5086.0374,884.91272.00275.315839.6521.47
5125.1637,078.94277.00133.86257.700.93
5278.16212,173.91264.00803.69211.150.80
5358.2112,562.93290.0043.321270.504.38
5485.944979.31290.0017.173028.6510.44
55102.884714.98323.0014.60570.871.77
56111.2712,773.01315.0040.552203.777.00
578.04960.06333.002.88134.020.40
5811.672107.69326.006.471130.253.47
596.291009.02337.002.99133.590.40
603.973857.71455.008.4857.320.13
614.22906.64378.002.40274.860.73
625.011113.59340.003.28316.240.93
636.381872.12315.005.94370.971.18
646.26774.67257.003.01309.991.21
658.131813.45288.006.30319.971.11
664.161277.76347.003.68109.160.31
673.30552.77393.001.41520.101.32
68724.0173,444.82195.00376.6427,674.86141.92
6955.8811,860.65195.0060.821099.355.64
7010.773715.11212.5017.4812,902.4760.72
7111.096281.46300.0020.9432,093.53106.98
729.03717.82230.003.12214.050.93
7311.234651.80265.0017.5519,891.3075.06
7436.532515.90300.008.3918,721.2362.40
751.85713.42292.502.44100.850.34
7628.1617,763.40290.0061.2521,823.6075.25
774.991316.94293.004.49NA NA
7815.151692.13343.004.93224.020.65
7939.603278.22347.009.45574.131.65
805.80733.04300.002.4462.300.21
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Khalil, M.M.; Mahmoud, M.; Alexakis, D.E.; Gamvroula, D.E.; Youssef, E.; El-Sayed, E.; Farag, M.H.; Ahmed, M.; Li, P.; Ali, A.; et al. Hydraulic and Hydrogeochemical Characterization of Carbonate Aquifers in Arid Regions: A Case from the Western Desert, Egypt. Water 2024, 16, 2610. https://doi.org/10.3390/w16182610

AMA Style

Khalil MM, Mahmoud M, Alexakis DE, Gamvroula DE, Youssef E, El-Sayed E, Farag MH, Ahmed M, Li P, Ali A, et al. Hydraulic and Hydrogeochemical Characterization of Carbonate Aquifers in Arid Regions: A Case from the Western Desert, Egypt. Water. 2024; 16(18):2610. https://doi.org/10.3390/w16182610

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Khalil, Mahmoud M., Mostafa Mahmoud, Dimitrios E. Alexakis, Dimitra E. Gamvroula, Emad Youssef, Esam El-Sayed, Mohamed H. Farag, Mohamed Ahmed, Peiyue Li, Ahmed Ali, and et al. 2024. "Hydraulic and Hydrogeochemical Characterization of Carbonate Aquifers in Arid Regions: A Case from the Western Desert, Egypt" Water 16, no. 18: 2610. https://doi.org/10.3390/w16182610

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