A large number of groundwater analyses exist in the archives of the Ministry of Water and Irrigation ([9]) and serve as monitoring data to control the water quality in the aquifers and to guarantee a safe water supply for the inhabitants. Many M.Sc. and Ph.D. theses carried out under the authors’ supervision, in addition to published research works containing detailed analyses of the groundwater in specific areas of the country, will also be used in this study as important sources of information. Such information is taken from: [17]; [5]; [7]; [10]; [19]; [16]; [20]; [1]; [8]; [2]; [15]; [14]; [6]; [12]; [13]; and many others. These works concentrated on specific areas and discussed the existing status of groundwater quality. In Jordan, only a few studies have tried to explain the evolution of the natural groundwater composition ([12]; [15]; [14]; [17]; [16]).

This study aims to explain the natural evolution of the different water qualities in the Upper Cretaceous to recent aquifers, because of water-rock and water-water interactions, in order to understand the mechanisms leading to the formation of the different water qualities. It also aims to reach recommendations for the sustainable management of the aquifers and to limit their deterioration by the mobilization of salts contained in the surrounding rock formations.

This series of rocks (A1-6) comprises limestone, dolomite, marl, chalk, and shale beds of more than 300 m thick (Table 2, Figure 2). It overlies the deep sandstone aquifer system composed of Lower Cretaceous to Precambrian clastic sediments, which in turn overlies the Precambrian granitic basement. The series contains thick beds of fractured and karstified limestone building local aquifers, such as the Hummar Formation (A4) or the limestone beds forming parts of the Na’ur and Fuheis Formations (A1-3). The series, as a whole, forms a poorly developed aquifer, but on a regional scale, it hydraulically connects the overlying aquifers (Massive Limestone and the Silicified Limestone (A7/B2)) with the underlying deep sandstone aquifer complex (Lower Cretaceous and older clastic rocks). The series contains, locally, gypsum layers of up to a few meters in thickness in addition to thin gypsum layers and patches within the clay layers. Other evaporite residues are also found in the rock series.

This sequence consists of a series of thick, massive limestone beds overlain by phosphate rocks and cherts with a total thickness of 200 - 300 m, possessing very high porosity and permeability. In some areas, the B2 Formation is separated from the A7 Formation by the Um Ghudran Formation (B1), a very poor aquifer, which has a thickness of 0 - 35 m (Table 2). The rock series covers extensive areas along the high mountains of Jordan, extending from the Ras en Naqab area in the south to Jordan’s borders with Syria in the north and from the eastern escarpment of the Jordan Rift Valley area in the west, eastwards beyond Jordan’s borders. In the eastern plateau area, a thick aquiclude, the Bituminous Marl Formation (B3), overlies the A7/B2 and confines its groundwater (Figure 2).

The Muwaqqar Bituminous Marl Formation (B3) of late Upper Cretaceous–early Tertiary age crops out extensively along the Plateau area of Jordan. It forms a major aquiclude separating the surficial aquifers (B4,5,6, the recent basalts, and Quaternary sediments) from the Upper Cretaceous aquifers (A7/B2). The B3 confines the underlying aquifer systems (Figure 2, Table 2) and is generally overlain by chalk marls of Paleocene to Eocene age, which, together with recent basalts and sediments, form a surficial aquifer.

To the north of the northern latitude of the Dead Sea to around 25 km south of the Yarmouk River, the Bituminous Marls have been eroded and are only found in patches. The formation builds an aquitard of up to 300 m thickness, and in Jafr Depression, it even reaches around 800 m ([4]; [11]).

The Rijam and Shallala (B4,5) Formations consist of marl and chalk beds with some thin chert beds, generally less than 20 cm in thickness. They cover large parts of the highlands of Jordan to the east of the Jordan Rift Valley Shoulder Mountains, overlying the thick aquiclude of the Bituminous Marl Formation (Figure 2, Table 2). In the Azraq area and its surroundings, the Um Qirma Formation (B6) overlies, in places, the Shallala and Rijam Formations. The B6 consists mainly of sandstone and siltstone, generally about 40 m thick, and contains no water. Rijam and Shallala form Jordan’s local surficial aquifers and receive direct recharge from precipitation and flood flow water along their outcrops. In some areas, such as Azraq, Mafraq, and partly Jafr, this formation is found covered by basalts and/or recent sediments.

The B4,5 Formations cover five main areas in Jordan: Jafr, Sirhan, Hammad, Azraq, and Yarmouk (NW of Irbid). Recent, mainly alluvial, sediments of Quaternary age cover the B4,5 and the basalts, in places, forming local surficial aquifers.

The Upper Cretaceous aquifer consists of argillaceous limestone. This poorly developed aquifer receives very limited amounts of direct recharge from precipitation or flood flows. Its groundwater originates from the downward percolation of groundwater in the overlying aquifers, mainly from the A7/B2 aquifer. Due to the presence of evaporite residues in Formations A1-3 and A5, 6, the salinity of the groundwater increases as a function of water residence time and, hence, interaction with the aquifer matrix, recharge/discharge mechanisms, and location relative to the evaporite residues concentrations within the rock formation. Therefore, the composition of the groundwater varies between that of the overlying A7/B2 aquifer, the source water, and water affected by evaporites. The A7/B2 groundwater is directly or indirectly (along wadis) recharged by precipitation water and its chemistry reflects its reaction with the carbonates rock sequence. But once it percolates into the underlying evaporates-containing poor aquifer sieries, the B1-6, its water chemistry changes radically to chloride-sulfate water.

Table 3(a) lists some of the analyses of the groundwater in the A1-A6 with their salinities, which range from about 845 to about 1210 µS/cm. In the Piper diagram (Figure 3(a)), the water of this group plots within the earth’s alkaline type with no dominant cations but is very close to sulfate and chloride waters. In the Durov diagram (Figure 3(b)), the water plots in the dissolution/mixing regime, but the geology, recharge, and discharge mechanism of the groundwater suggest dissolution of the rock matrix rather than mixing with other groundwater types, with Ca²⁺ ~ Mg²⁺ ~ Na⁺ > K⁺ and HCO 3 − > Cl⁻ > SO 4 2 − . Figure 3(c) shows the Schöller diagram in the Na’ur, Fuheis, Hummar, and Shueib Formations, A1-6. The scattering of the composition in the different diagrams reflects the spatial distribution of evaporates within the rock formations.

Table 3. (a) Composition of the A1-6 sampled water sources (EC in µS/cm; concentrations in meq/l); (b) Correlation matrix for the normal water component of in Na’ur, Fuheis, Hummar, and Shueib Formations, A1-6; (c) Saturation Indices (SI) of the main minerals in Na’ur, Fuheis, Hummar, and Shueib Formations, A1-6.

(a) Sp.: Spring.

(a)

(b)

(c)

Figure 3. (a) The Piper diagram of the water within the Na’ur, Fuheis, Hummar, and Shueib Formations, A1-6; (b) The Durov diagram shows the water plots in Na’ur, Fuheis, Hummar, and Shueib Formations, A1-6; (c) The Schoeller diagram shows the water Quality in Na’ur, Fuheis, Hummar, and Shueib Formations, A1-6.

The Na⁺/Cl⁻ and Ca²⁺ + Mg²⁺/ HCO 3 − + SO 4 2 − equivalent ratios are around unity , indicating the dissolution of the aquifer matrix containing evaporates, without ion exchange reactions. The correlation of the different parameters is very weak, reflecting the variability of the aquifer composition and its rapid change in space (Table 3(b)). The water in these rocks is slightly under-saturated with respect to calcite, dolomite, aragonite, and anhydrite, intermediately unsaturated with respect to gypsum, and strongly unsaturated with respect to halite (Table 3(c)).

Due to the low permeability of this sequence and hence the long residence time of the groundwater in the rocks, and due to its evaporate contents, the groundwater shows an increase in salt contents compared to the source water.

This sequence is the most important source of renewable groundwater in Jordan. Its water originates mainly from direct recharge along the extensive outcrops along the western highlands. Due to the composition of the aquifer, consisting of limestone and chert, and its long exposure to flushing by rainwater, its water is fresh and generally suitable for common use purposes.

The groundwater in this aquifer flows in two directions from its recharge area along the high mountains: to the west towards the Jordan Rift Valley, where it discharges from mountain springs, and eastwards, building a groundwater body underlying the Plateau area, where the thick Bituminous Marls (B3) confine it. This flow mechanism and its governing conditions entail different groundwater qualities; therefore, the two parts of the groundwater flow in the aquifer will be discussed separately.

4.2.1. Mountain Springs

Springs discharging from this rock sequence issue along the side wadis of the Jordan Rift Valley, extending from the Ras en Naqab area in the south to the Ajlun area in the north. Examples of the water quality are listed in Table 4(a), and their plots in Piper, Durov, and Schöller diagrams are in (Figures 4(a)-(c)).

The salinity of the groundwater is relatively low and ranges from around 500 to about 950 µS/cm. Water-rock interactions are restricted in time by the relatively fast recharge-discharge duration of around one year and by the mineralogical composition of the well-flushed composite aquifer of highly lithified chert, limestone, dolomite, and phosphate rocks.

In the Piper diagram (Figure 4(a)), the water plots in the earth alkaline type to earth alkaline type with increased portions of alkalis and prevailing carbonates. In the Durov diagram (Figure 4(b)), the water plots on the dissolution-evaporation line with no ion exchange processes between the water and the aquifer matrix. In the Schöller diagram, Figure 4(c), the ionic ratios are Ca > Mg >< Na and HCO₃ > Cl > SO₄. Worth mentioning here is that Salt and Hizzir springs are polluted by household wastewater as indicated by their high nitrate contents and hence their different plots in the diagrams.

Correlations are clear between Ca, K, and SO₄, Na and Cl, K and NO₃; the latter indicates domestic waste pollution (Table4(b)).

Table 4. (a) Composition of spring water issuing from the Massive Limestone/Silicified Limestone (B2/A7) composite aquifer along the highlands of Jordan (EC µS/cm, and all others in meq/l); (b) Correlation matrix for spring water issuing from the Massive Limestone/Silicified Limestone (B2/A7) composite aquifer along the highlands of Jordan; (c) Saturation Indices (SI) for spring water issuing from the Massive Limestone/Silicified Limestone (B2/A7) composite aquifer along the highlands of Jordan.

(a)

(b)

(c)

Figure 4. (a) The Piper diagram for the water in the B2/A7 Mountain springs in Jordan; (b) The Durov diagram for the water in in the B2/A7 Mountain springs in Jordan; (c) The Schöller diagram for the water in the B2/A7 Mountain springs in Jordan.

The water of these springs is ±saturated with aragonite, calcite, and dolomite, under-saturated with gypsum and anhydrite, and strongly under-saturated with halite (Table 4(c)).

4.2.2. B2/A7 Underlying the Plateau Area (Plateau Groundwater)

The recharge water in the Massive Limestone and Silicified Limestone aquifer system (A7/B2) that flows eastwards underground in the Plateau area becomes, at a distance of 20 - 30 km east of the mountains, gradually confined by the Bituminous Marl (B3) aquiclude. Due to long flow times and hence long water-rock interactions, and due to the confinement by the Bituminous Marl aquiclude, the groundwater gains salinity, which increases to more than 1000 µS/cm (Table 5(a)), and temperature, which rises to more than 40˚C ([2]). In addition, the groundwater in most wells has an HS smell, and contains high CO₂ gas concentrations because of microbial sulfate reduction within the confined parts of the aquifer.

The water composition plots in the Piper diagram as earth alkaline type with increased alkalis and prevailing chlorides. In the Durov diagram, the water plots on the dissolution/evaporation line with increased dissolution of the calcareous rock matrices compared with the springs’ water in the west. In the Schöller diagram, the water shows Na ⁓ Ca > Mg and Cl ⁓ HCO₃ > SO₄ (Figures 5(a)-(c)). The water is ± saturated with calcite, dolomite, and aragonite, under-saturated with gypsum and anhydrite, and strongly under-saturated with halite (Table 5(b), Table 5(c)).

Table 5(b) shows high correlations between Ca, Na, and SO₄, Na and Cl, and Cl and SO₄, which indicates the dissolution of the aquifer matrix. All of the above indicates recharge water, which has reacted with a calcareous rock matrix and become confined under reducing environments.

Table 5. (a) Composition of groundwater in the Massive Limestone/Silicified Limestone (B2/A7) composite aquifer underlying the Plateau area of Jordan (EC µS/cm, NO₃ in mg/ land, others in meq/l); (b) Correlation matrix groundwater in the Massive Limestone/Silicified Limestone (B2/A7) composite aquifer underlying the Plateau area of Jordan; (c) Saturation Indices of groundwater in the Massive Limestone/Silicified Limestone (B2/A7) composite underlying the Plateau area of Jordan.

(a)

(b)

(c)

Figure 5. (a) The Piper diagram for the water in the B2/A7 Plateau area; (b) The Durov diagram for the water in in the B2/A7 Plateau area; (c) The Schöller diagram for the water in the B2/A7 Plateau area.

Its primary porosity is very low, less than 10⁻⁷ m/s. In some areas, it possesses secondary permeability, allowing for hydraulic interconnections of the overlying and underlying aquifers’ groundwater. No springs or wells are producing from this aquiclude, but it has quality impacts on overlying and underlying aquifers due to its bitumen contents and its confinement of the underlying groundwater bodies.

This Chalk Marl Formations (B4,5) aquifer crops out in five main areas in Jordan, namely Jafr, Sirhan, Hammad, Azraq, and Yarmouk (NW of Irbid) (Figure 1), where the thick aquiclude of the Bituminous Marl Formation (B3) underlies them. Only in the Azraq Depression does the Um Qirma Formation (B6), consisting of sandstone, chalk, and chert nodules, cover small areas of the B5 with a thickness generally up to 40 m. The B6 Formation does not contain groundwater bodies.

Recent basalts of Harrat esh Sham and recent alluvial deposits cover the B4/B5 Formations in parts of the Hammad and Azraq areas, which results in the groundwater there having different hydrochemistry compared to the Jafr, Sirhan, and Yarmouk areas.

The groundwater in this composite aquifer is generally fresh, except in playa and mudflat environments, where evaporation has left behind salty grounds so that the groundwater in the surroundings becomes slightly brackish (Table 6). Therefore, due to the direct effects of differences in climatic conditions, topographic constellations, and geologic settings on this surficial aquifer, its water quality in different parts of the country differs. Hence, its quality evolution will be considered for each area separately.

Table 6. (a) Analytical results of the major constituents of the composite B4,5, basalt, and recent sediments groundwater sources (EC in µS/cm; NO₃ in mg/l, other concentrations in meq/l); (b) Correlation matrix of the major constituents of the composite B4,5, basalt, and recent sediments groundwater sources; (c) Saturation Indices (SI) for the major constituents of the composite B4,5, basalt, and recent sediments groundwater sources/

The salinity of the water ranges from less than 1000 to 2700 µS/cm (only Hammad, H1055 has an EC of 3200 µS/cm (Table 6(a)). The water composition of all samples plots in the Piper diagram in the earth alkaline type with increasing portions of alkalis (Figures 6(a)-(c)). However, in Jafr Surroundings, Sirhan, and Yarmouk, the water shows only very slightly prevailing sulfates and chloride (Cl + SO₄ ≈ 55% - 70% of the anions and Ca + Mg ≈ 50% - 80% of the cations) relative to Azraq and Hammad groundwaters, which show strongly prevailing sulfates and chlorides (Cl + SO₄ > 75% of the anions and Ca + Mg ≈ 30% - 60% of the cations).

(a)

(b)

(c)

Figure 6. (a) The Piper diagram of the water in the Chalk Marl Formations; B4/5 (Rijam and Shallala) and the Sandstone Formation; B6 (Um Qirma in Azraq area), the basalt aquifer and the recent sediments of the highlands; (b) The Durov diagram of the water in the Chalk Marl Formations; B4/5 (Rijam and Shallala) and the Sandstone Formation; B6 (Um Qirma in Azraq area), the basalt aquifer and the recent sediments of the highlands; (c) The Schoeller diagram of the water in the Chalk Marl Formations; B4/5 (Rijam and Shallala) and the Sandstone Formation; B6 (Um Qirma in Azraq area), the basalt aquifer and the recent sediments of the highlands.

In the Durov diagram, all the water plots on the evaporation/dissolution line or very close to it, which indicates the absence or minimal presence of ion exchange processes.

Although the composition of this composite aquifer groundwater plots in the different diagrams in the same classification type, it shows important differences within these plots.

Azraq and Hammad groundwater generally shows high salinities compared with Jafr Surroundings, Sirhan, and Yarmouk groundwaters. Jafr Surroundings, Sirhan, and Yarmouk groundwater plots in the Piper diagram are in the area of earth alkaline water with increased portions of alkalis and some sulfates, whereas in Azraq and Hammad, sulfates and chlorides strongly prevail. Jafr Surroundings, Sirhan, and Yarmouk water show ionic ratios of Ca ≈ Na > Mg and Cl > HCO₃ > SO₄, whereas that of Hammad and Azraq shows Na ≥ Ca > Mg and Cl > SO₄ > HCO₃, reflecting the effects of strong evaporation from playa and mudflat environments, leading to the higher concentrations of the groundwater on evaporates and eventual precipitation of gypsum.