Iraqi Geological Journal

Abstract


Introduction
The study area is of local economic and agricultural importance. Euphrates River passes through the area and branches into two streams: Kufa and Abbasia. Both serve as the main source of surface water at the northern borders of the study area. The same two branches have different names on the southern border of the study area: Sabeel and Atshan. A historical natural lake (Sawa) is located in the western part of the study area. The area also contains several natural springs and semi-deep wells exploited for the cultivation of rice, barley, and some other vegetables. Atshan River meets Sabeel River on the southern border of the study area and reunion to form the main Euphrates River approximately 10 km upstream of Samawa city.
The Quaternary sediments cover all the parts adjacent to the Euphrates, which include the Pleistocene and Holocene deposits. Whereas, the exposed Pre-Quaternary sediments range from the Paleocene to the Pliocene which includes Dammam, Euphrates, Nafayl, Fathah, Injana, Zahra, and Dibdiba Formation, (Barwary & Slewa, 1995). Other authors (AL-Rawi & Al-Hadithi, 1968) investigated the geology and the salinity of Sawa Lake. Al-Rawi (1975) studied the hydrogeology of the area near the Sawa lake and the salt deposits around the lake, indicating that the lake is fed by the ground waters of the Euphrates and Dammam layers and its water chemistry is unique among the Iraqi lakes. The most important structural elements distributed in the area are faults with different directions, East-West, Northwest-Southeast, and North-South. These faults cross with each other creating a weak area represented by the presence of springs along with its extension (Buday & Jassim, 1987). (Al-Shemari, 2006) conducted a study to assess the hydro-geological and hydro-chemical conditions of the Rehab area, south and southwest of the study area. In a local study, (Abdul-Razzaq et al., 2013) studied the hydro-geological situation in Shanafiya-Samawa using hydro-chemical and radioisotopes techniques, to evaluate the effect of the groundwater of the above area in addition to the effect of Sawa Lake on the water of the Atshan River. (Al-Mitawki, 2013) studied the effect of water drainage on groundwater and surface water quality in the Shanafiya area, using hydrochemistry and radioisotope techniques. The area was also studied by (Al-Qurishi, 2014) who focused on the hydrochemistry of Sawa Lake, and showed that the lake water quality is of marine origin mixed with rainwater and originates from the underlying Formation, (Ali & Ajeena, 2016). Finally, the same area was studied for interaction between surface and groundwater by using the environmental isotopes technique (Al-Naseri et al., 2023). The main objective of this study is to reveal their possible mutual interaction between surface water and ground water using hydro-chemical technique.
The work plan focused on uncovering the relationship between groundwater and surface water of the Euphrates River, which represents the water limit for groundwater coming from underground aquifers located in the desert region towards the sedimentary plain through chemical analyses. Also, the possibility of a relationship between the groundwater of semi-deep and shallow wells, and the scattered drainages in the study area, as well as the existence of a correlation or relationship between the surface water existing as lakes with the river water.

Location of the Study Area
The study area is located in the southwest of Iraq, between two big cities: Kifl and Samawa, which are bounded by Longitudes (44⁰00' -46⁰16') and latitudes (30⁰44' -32⁰30'). Generally, the climate in the region is characterized as hot and dry in summer, and cold in winter, with an average annual temperature for the period 2012-2017 is 23.5 ˚C (Abbas et Al., 2018). The area is also characterized as a semi-arid area with an average annual relative humidity of (38% -41%). The annual rate of evaporation is 3200-3500 mm (Abdul-Razzaq et al., 2013), whereas the annual average precipitation is 75-100 mm (Abbas et Al., 2018). All the water sampling sites are represented in the location map, (Fig. 1).

Geology and Hydrogeology of the Area
Structurally, the western part of the study area is located within the Stable Shelf (Arab-Nubian platform), while the largest eastern part is located within the Unstable Mesopotamian Shelf which is covered by the Quaternary sediments of flood plain that contain alternating layers of clay, silt, gravel, and sand. In addition, the sediments of the Euphrates River Basin cover part of the study area. The thickness of this water-bearing layer in the study area may reach up to 20 meters (Abdul-Razzak et al., 2013). The most important component of such sediments is gravels and sands, which are porous and permeable and provide a possibility of a hydraulic connection between groundwater in this layer and the underlain layers (Dammam aquifer), (Abdul-Razzaq et al., 2013, Al-Jiburi and Al-Basrawi, 2011, Krasny & Selim, 1982. Fig.2, shows the geological map of the study area (Awadh et. al 2014), while Fig.3 shows a Lithological section of one of the wells in the study area, (General commission for ground water modified by Abdul-Razzaq and Al-Naseri, 2019).
Groundwater is found in different rock layers, and it exists at different depths as well. Therefore, it is greatly affected by the physiographic situation of the region and the geological structures such as fault and fracture systems. For instance, groundwater is present in the study area at medium to high depths in both the Dammam and Euphrates Formations, while it is located in shallow depths close to the surface in Recent Quaternary deposits, (Abdul-Razzaq et al., 2013).
springs are one of the distinctive phenomena that appear in the study area. They are considered one of the main resources for the population, especially when surface water is scarce or absent. The existence of such springs is due to the structural and geological nature of the region, which is located and organized on the eastern edge of the Western and Southern Sahara, parallel along the Euphrates River and in the direction of the northwest-southeast, which reflects the influence of the Euphrates fault line where the study area is included, (Al-Basrawi et al., 2018). The source of these springs is water flowing from the bottom (the Dammam Formation or the deeper rocks), passing through the cracks and caves of the claystone and anhydrite up to the Recent sediments on the surface.

Materials and Methods
The fieldwork includes collecting different kinds of water samples from different locations in the study area (Rivers, Lakes, Drainages, Shallow-wells, Deep-Wells, and Springs). A total of 113 samples were collected from 113 sites spread within the study area as shown in Fig.1. The samples included 26 river water, 33 samples from deep wells, 14 samples of shallow wells, 11 from drainages, 4 samples from lakes (2 from Sawa lake and 2 from Bahr Al-Najaf) and 25 samples of springs. The hydro-chemical analysis was in the laboratories of the National Center for Water Resources Management, the Iraqi Ministry of Water Resources. The analysis included the determination of cations (Ca +2 , Mg +2 , Na +1 , K +1 ) and anions (Cl -1 , SO 4 -2 , HCO 3 -1 , CO 3 -2 , NO 3 -1 , B -1 ). Electrical conductivity (EC), the concentration of total dissolved solids (TDS), and pH were measured as well.
The verification of the results was conducted by calculating the absolute error that may be caused by the method of work or interference during the analyses. The method described by (Appelo & Postma, 2005), was used for this purpose by determining the percentages of the possibility of relying on the results of chemical analyses in preparing hydro-geochemical interpretations by using the following equation: Whereas, U% represents the difference in relative error. If the absolute value of the relative difference was less than 5%-10% the results are good and accurate, while if it was more than 10%), then one cannot rely upon it in the interpretation process. Table 1 lists the results of the chemical analysis of water samples. The values were expressed in weight concentration (parts per million, ppm). Applying the relative difference equation, it was found that all the obtained analysis values fall within the permissible limits (5%-10%).

Results and Discussion
The analysis applied the Karloff equation 2 using equivalent per liter, epm (epm=ppm/Eq. weight), (Abdul-Razzaq & Al-Naseri, 2019; Ahmed & Abdul-Razzaq, 2005). The samples were categorized into two main groups: the sulfates group, for 67 samples (60% of the total samples), in which Calcium sulfate (CaSO4) characterizes 40 samples, sodium sulfate (Na2SO4) characterizes 26 samples and only one sample was characterized by magnesium sulfate (MgSO4). The second group is the chlorides group for 46 samples (40% of the total samples), and this group includes two types of salts: NaCl for the majority of samples (45 samples), and CaCl 2 for only one sample. Table (2) shows the types of water mentioned in the above analysis and their locations. ( 2) The results showed that drainage water, in general, contains predominant concentrations of NaCl, except that sulfate concentrations in the river exceed those in the chlorides of these drainages, making it the dominant one in the rivers. On the other hand, although CaSO4 is predominantly present, we note that Na2SO4 also takes dominance, especially in river samples, and therefore, indicates the absence of contact between deep well's water and springs containing calcium sulfate with both river's branches (Atshan and Sabeel). Fig.4 shows histograms of the major five elements analysis, (Ca, Mg, Na, SO4, Cl).
The pH values of all the samples have a range between 8.33-6.75, which confirms that the water is between slightly acidic and light alkalinity. The concentrations of TDS range between 758-88020 mg/l. The range of TDS in the Euphrates, Sabeel, and Atshan Rivers reached 782, 758-2650, and 900-1640 mg/l, respectively. The TDS concentrations of the spring's water range between 3510-78630 mg/l. It was found that the most important characteristic of shallow well water from rivers, springs, and/or deep wells is the ratio of chloride ion concentration (Cl), which is characterized by having a range of 397-4680 mg/l. This increase in concentration is offset by a difference in the concentration of the water in the Euphrates River, mostly for the sulfate ion with the range 207-922 mg/l instead of chloride and boron ions of the range 0.28 -0.79 mg/l.  In general, the results show that groundwater has no effect on the surface waters of the Atshan and Sabeel Rivers in the area between Shanafiya and Samawa due to the great differences in the concentrations of chloride and boron ions. On the other hand, the increase in the salinity in the Atshan River upstream of its meeting location with the Sabeel River may be attributed to the spring's drainage, which flows into the Atshan River. The shallow wells' results showed no relationship with those of the deep ones because each group represents a separate geological aquifer (one of which is the Mesopotamian plain sediments and the other is Dammam). Table-1 shows that the quality of the Euphrates water, from Kifl to upstream Shanafiya city is calcium sulfate (CaSO4). In deep wells, water passes through Al-Rus Anhydrite Formation that separates the Dammam and Umm_Radhuma Formations. This layer includes cracks and cavities, which make a hydraulic medium that drives deep water from the bottom to the top layer, in and downstream, of Shanafiya city. The chemical characteristic of the river water changes from (CaSO4) to (Na2SO4), meaning that the sodium ion replaces the calcium ion. This change is due to the possibility of dissolving halite salts that exist on the ground surface soil because of rain or the flow of irrigation channels into the river. Thus, the quality of the water containing (Na2SO4) shall be dominant from Shanafiya to Samawa city. On this basis, the predominant groundwater quality is (CaSO4), while the predominant characteristic of the surface water quality in the Sabeel and Atshan is (Na 2 SO 4 ). This gives an indication and evidence that there is no mixing between the groundwater of the springs with the river water. On the other hand, the results showed a similarity between springs and deep wells that indicates the presence of contact and recharge of groundwater from Dammam or Umm_Radhuma subsurface aquifers to those springs. In general, and based on the previous analysis, the above explanation can be divided into two levels, the first highly saline level is represented by the waters of the observation (shallow) wells with depths of (8 m), Sawa Lake, some springs, and the level of average salinity that is represented by deep well water and some springs as well. The source of the water in the second level is due to Al-Dammam Formation, or the Formation of Umm_Radhuma through the Al-Rus Anhydrite Formation. While the source of the first level of water with high salinity concentrations is coming from the Dammam Formation, which is located below the surface layer (Quaternary sediments) that extends in the direction of the two branches of the Euphrates River. The  -Jiburi and Al-Basrawi, 2008), which in turn produce greater opportunities for water to penetrate through soils rich in chloride and boron ions, in which an increase in salinity occurs due to the evaporation process. It is worth noting that the nitrate ion (NO3) has very low concentrations and has a value ranging between (2-7) mg/l, over the entire study area from Kifl to Samawa cities. The low concentrations of this ion indicate that there is no significant pollution in the water of rivers, drainages, and deep and shallow wells.

Relationships between Surface Water and Monitoring Wells
To present additional chemical evidence about the lack of interaction between groundwater and surface water (rivers), Fig.5 shows the relationships between the group of positive ions (cations) and negative (anions) with the TDS concentrations to investigate the strength and weakness of those relationships to evaluate the characteristics of water-bearing layers.
The figure shows strong correlation coefficients (R 2 = 0.973 and 0.983) between the TDS and both the sodium (Na) and the chloride (Cl) respectively. It reflects the strong relationship between (Na and Cl) which was calculated to be (R 2 = 0.99). The relationship between the TDS with the sulfate ion (SO4) and the calcium (Ca) shows values of (R2 = 0.464 and 0.726) respectively. This indicates that the source of the chloride ion is the dissolution of the halite salts (NaCl) mixed within the surface soil particles and flushing by rain, especially those located within the sedimentary plain. This is another feature, which explains that the groundwater within the sedimentary plain aquifers contains concentrations of NaCl salts. When comparing both relationships' results, it can be noticed that the correlation coefficient for salts (CaSO4) is weak and reversed, while the relationship (Na2SO4) is strong. So, the predominant salts are (Na2SO4) and the increase in salt concentrations (TDS) is attributed to the increase in the sulfate and sodium ion, this is shown by the strong bond or relation between TDS -SO4 and TDS -Na.

TDS (mg/l)
Ca ppm Mg ppm SO4 ppm Na ppm Cl ppm

Relationships between Surface Water and Springs
The relationships for spring's water are shown in Fig.6. This Figure revealed that the majority of water is (CaSO 4 ), based on the strength of the relationship between (Ca) and (SO 4 ) that equivalent to (0.907). The increase in the sulfate ion is because its source originates from the Al-Rus Anhydrite Formation, where water rises from the Umm_Radhuma Formation through Al-Rus, which includes cracks and caves that lead to a hydraulic connection between the layers lie below and above it. Although the increase in TDS is a result of the increase in the chloride ion, which is more than the relationship of TDS -SO4.  Fig.8 shows that the value of the relationship of the TDS concentrations with each of the sodium (Na) ion, the chloride ion (Cl), and the sulfate ion (SO4) is strong, which is equivalent to a range located between (R2 = 0.96 and 0.99). This indicates the presence of a mixture between the quality of the groundwater to dissolve the (NaCl) rich halite in the Sabkhat scattered in the region and the calcium sulfate salts that come from the Umm_Radhuma aquifer through the Formation of Al-Rus which is connected hydraulically with Dammam Formation. We would like to point out here, that the increase in TDS concentrations comes from the abundance of sodium ions even with the abundance of chloride and sulfates. However, given the water quality in Sawa Lake, which is rich in salt concentrations of NaCl and CaSO4, where these two types have a weak relationship with the Atshan River of quality (Na2SO4). So, this indicates that there is no effect of Sawa Lake on the surface waters of the Euphrates.

Relationships between Surface Water and Drainage
Finally, Fig.9 and Fig.10 show the relationship between salts concentrations of the drainages and river water samples distributed in the study area. It can be noticed that the relationship of the TDS concentrations with each of (Cl), and (SO 4 ) which shows a range between (0.887 and 0.978), as well as the strength of the relationship between Na and Cl which is equivalent to the parameter (1.0). A medium strength relationship was shown between the calcium and sulfate ion, equivalent to the parameter (R2 = 0.781) whereas a fair relationship between Ca and Mg was shown either. It is clear from both figures that the trend of the distribution of the ions in both the drainage and river water samples is the same but shifted to a higher TDS concentration for the drainage water sample. This is expected since the source of the drainage water is the river water

Conclusions
It can be concluded from the above analysis that there is no or at least a very weak relationship between the groundwater with the Euphrates River Water in the study area. In addition, there is no effect of the shallow salty water on the quality of the river water. The results indicate the presence of two levels of water depending on the concentration of the TDS: the first is the highly saline level represented by the water of shallow wells in which salinity increases due to evaporation between (7000 -110,000 mg/l). The second is the water of medium salinity (1500 -4000 mg/l) represented by the water of semideep wells and springs, whose source is Umm_Radhuma and Dammam aquifers across the Al-Rus Anhydrite Formation. The water of the first level is characterized by the presence of high percentages of chloride and boron ions. In addition, Sodium was considered the main characterization factor to indicate the extent of the effect of groundwater on the Atshan River. The second level of water was characterized by the predominant sulfate ion, from which it can be inferred that there is a very weak effect on the river water. The results also showed an increase in the TDS concentration in the Atshan River (one of the two branches of the Euphrates River) with the course of the river from the north to the south. This is due to the mixing with the drainages' water that moves in parallel to the Atshan River and pours into it.

TDS (mg/l)
Ca ppm Mg ppm SO4 ppm Na ppm Cl ppm