Hydrogeochemical properties and the exhaustion groundwater reserve from Dammam aquifer at Al-Najaf Governorate, middle Iraq

One of Iraq’s most significant groundwater-bearing limestone aquifers is the Dammam Formation. The aquifer groundwater has been studied hydrogeochemically. It is suitable for irrigation, as indicated by sodium adsorption ratio (SAR) and total dissolved solids (TDS), which are 4.15 and 1971 ppm (in average) respectively. Through the vision of the Stiff diagram, the predominant ions are Cl-, SO4 2+ and Na+ while the HCO-3 and Mg2+ are relatively poor. There is plenty of flowing wells in the study area in Najaf Governorate producing groundwater from the Dammam aquifer. In recent years, many wells have been drilled in an irregular pattern for forming fish breeding lakes. These lakes’ water drains 4.715 m3/s into the Najaf depression by Wadi Al- Khur and artificial channels, where it mixes with brine water, rendering it useless. This lead to the exhaustion huge amount of precious groundwater resource. Many signs that confirm the Piezometric pressure drop and groundwater levels descent in the Dammam aquifer in the region. The groundwater flow has been halted in several flowing wells in the study area especially in Wadi Al-Khur due to the exhaustion of the reserve and a decrease in the level of the hydrostatic pressure of the aquifer. A significant decline in values transmissivity and specific capacity of the Dammam aquifer when compared with previous studies in the years 1996 and 2009. Through observation of the monitoring well (W/7), a decrease in groundwater levels of flowing wells in the study area.


Introduction
Groundwater is any water, which confined beneath the surface of the earth in aquifers. It spreads over a wide territory in numerous places [1]. It may be near the Earth's surface or as deep as 1000 m, according to the U.S. Geological Survey (USGS). This water is not always accessible or may not be fresh enough for human activities without treatments and it is sometimes difficult to locate, identify and describe it as an aquifer. The dissolution of gypsum, calcite, dolomite, halite as well as silicate weathering Control the hydrochemistry of groundwater, which is represented by the ionic exchange between groundwater and clay minerals [2]. The Bahr Al-Najaf province is characterized by its possession of a huge and unique basin of groundwater with good physical, chemical, and biological properties. The Dammam Formation (Middle Eocene), which consisting of limestone, which its character by an especial of secondary porosity with secondary porosity is represented as the major aquifer in the province. It is characterized by the presence of the many caves and connected channels that help to transference groundwater at a good speed in addition to the presence of rooms and very large gaps [3].
The presence of faults and fractures in the water-bearing rocks in the Dammam Formation, especially in the province of Bahr Al-Najaf, has added an exceptional and unique advantage in the transporting process of groundwater and increasing the flowing wells drainage in the region.
The scarcity and deficiency of surface water resources, which are limited to a very narrow zone, in Bahr Al-Najaf province, because of a desert nature. The groundwater extraction and investment have been resorted to in several areas such as its use in the field of agriculture and industry, such brick factories, domestic uses, drinking water for human various animals.
The study area is located in the middle of Iraq at Al-Najaf Governorate in the west southwest of Al-Najaf city. It is restricted between coordinates longitude 43°55'51.88" E-

Geological framework of the area
Geomorphological, the presence of some prominent reliefs, which height of the land in it ranges between 8 and 65 m above sea level approximately, is characterized the study area. The height of the Najaf lands increases in the direction of the western reaches 420 meters above sea level at the Iraqi-Saudi frontier. The land slopes gradually from the west and southwest towards the north and northeast [4]. Some of the marsh depressions are located in the eastern part of the study area, which is adjacent to Tare Al-Najaf. It is located on the eastern side of the study area, which represents the lowest point for collecting water from its various and varied sources.
Generally, some valleys that drain rainwater are present in the study area from the west and southwest to the eastern and northeastern directions. Their water drained in the marshes of the Bahr Al-Najaf region, which coincides with the direction of the slope of the topography of the land such as Wadi Al-Khur, Wadi Haussab, Al-Rhimawi, Milih, and Abo Kumssat Valleys [5]. Geologically, the study area is located within the Al-Salman subzone boundaries, which is a part of the Stable Shelf Zone [6]. Two huge deep faults trending NW-SE, which extend in the study area, played an important role in controlling the movement of groundwater [7]. The existence of the springs is considered good evidence of the presence of these deep faults [8].
Stratigraphically, the formations of the region, which belong to the tertiary period. They started from the surface downward Euphrates, Dammam, Rus and Umm Er Radhuma formations that is covered by Quaternary deposits in major places [9] (Fig. 2).  The rock component of these formations forms most layers that carrying and affecting on the groundwater chemistry, which has hydraulic characteristics that distinguish them from each other in their ability to store, transport and discharge this groundwater.

Materials and Method
Twelve wells were selected to investigate the physical and hydrogeochemical properties of groundwater in the study area (Table 1).

Results and discussion
The results of the physical and geochemical analyzes of groundwater samples are listed in Table 2. Fig. 3 is represented Pie diagram showed the average percent of ionic constituents (epm %) of groundwater in studied wells.

ܷ% = ‫ݎ([‬ ‫݊݅ݐܽܿߑ‬ − ‫ݎ‬ ‫)ݏ݊݅݊ܽߑ‬ / ‫ݎ(‬ ‫ݏ݊݅ݐܽܿߑ‬ + ‫ݎ‬ ‫])ݏ݊݅݊ܽߑ‬ * 100
Where U is the uncertainty, r is a value in equivalent per mil (epm). When U (as absolute value) ≤ 5, the result could be accepted, but if 5 < U ≤ 10 the result will be accepted with risk [12]. The average value of U is 0.11 that means the analysis results are accepted.
The ionic constituents that predominated in the groundwater are SO 4 2and Clas anions and Na + , Ca 2+ and Mg 2+ as cations.
Through the vision for the Stiff diagram, which suggested by [13], the anion Cland SO 4  (Fig. 4). Through the vision of the Stiff diagram, the predominant ions are Cl -, SO 4 2+ and Na + while the HCO 3 and Mg are relatively poor.

Fig. 4: Stiff diagram (for average) of studied groundwater
The electrical conductivity values refer to groundwater mineralization. EC is the ability of an electric current to connect through 1 cm 3 of water at 25˚C [14]. The average of Ec in studied wells is 3015 μs/cm on average ( Table 2). Depending on [15] classification (Table 3), the groundwater of the Dammam aquifer is slightly mineralized water (limestone terrains) due to interactions between limestone rocks and groundwater in the Dammam Formations depending on its lithology.
The TDS values of the groundwater in the study area are (1971.04 ppm) in average ( Table   2). It refers that the groundwater in the study area is classified as brackish water as [16] classification (Table 4). It is not appropriate for drinking water depending on [17]. The studied groundwater has a pH (7.16) which is mean neutral.  Table 4: Classification of water salinity according to the TDS [16].
Water type TDS (ppm) Fresh water < 1000 Brackish 1000-10,000 Saline 10,000-100,000 Brine > 100,000 The groundwater of studied wells is appropriate for irrigation by using the sodium adsorption ratio (SAR) [18]. The SAR result (in average) 4.15 (Table 2) indicates that the water class is excellent for irrigation [14] ( Table 5).

Using groundwater for breeding fish
The groundwater of the Dammam aquifer has been invested in establishing multiple lakes for fish breeding. These lakes are fully supplied from groundwater by drilling unofficial and Irregulars flowing wells. Most of the lakes are concentrated in several locations of the study area and on both sides of Wadi Al-Khur. This area is an intersection between the Abu Jir fault, towards the northeast of the southwest, with the Al-Rhimawi -Hilla fault, towards the northwest of the southeast, in addition to many rock cracks, which facilitate the movement and transportation of groundwater to flowing wells in the areas. The Fish breeding lakes are either regular lakes with dimensions (40 m * 100 m) with a depth ranging between 1and 1.5 m or irregular shapes and large areas. These lakes consume large amounts of groundwater, and the fate of this water is either to evaporate or to drain into the marshes of the Najaf marshes through the Wadi Al-Khur or some channels that have been constructed by the excavators (Fig. 4). The amount of drained water from the fish breeding lakes towards the Najaf marshes reaches 4.715 m 3 / s [19].  Fig. 5: Drain channels of fish breeding lakes to Najaf marshes.

Piezometric pressure drop sign in Dammam aquifer
The piezometric pressure is the amount of water pressure inside the confined groundwater layer resulting from the difference in the height of the water level between two points, which is equal to the atmospheric pressure [20]. The piezometric pressure may be higher than the ground level in some areas, which results in the emergence of flowing wells like the Dammam aquifer.
There are many signs confirm the Piezometric pressure drop and drop of groundwater levels in the Dammam aquifer in the region. a. The groundwater flow has been halted in several flowing wells.
In the last years, the demand for drilling flowing wells to create fish breeding lakes has increased. All the flowing wells have been flowing large amounts of groundwater to fish breeding lake projects in the region. The ground level is descending towards the Wadi Al-Khur with a level difference of up to 30 m, this caused halted many wells flow of groundwater due to exhaustion of the reserve and a decrease in the level of the hydrostatic pressure of the aquifer (Fig. 5).  The hydraulic specifications of the groundwater-bearing aquifer layer are very important to identify the characteristics of the aquifer and its permanence. They obtained it by conducting a pumping test for wells that penetrate the water-bearing layer. Pumping test is operating a pump for particular hours, monitoring the decrease in the water level inside the well against time, and then analyzing these readings to obtain the hydraulic specification for the aquifer such as Hydraulic conductivity (K), Transmissivity (b) and storage capacity (Sc) [21]. The pumping test process was carried out for twelve wells penetrating the Dammam aquifer in different locations in Bahr Najaf Province (Fig. 1) Tables (6 and 7).   Recently, many farmers suffer from a decrease in groundwater levels in their wells that were drilled by them for agriculture, which forced farmers to drill new wells or increase the depth of these wells. There is two kinds of the decrease in groundwater levels in the area. 8 A-Seasonal reduction in groundwater that occurs during the wheat cultivation season, which necessitates an increase in the demand for groundwater extract for irrigation of crops.
B-General decrease in the levels of the aquifer water due to the increase in drilling wells and the expansion in the land areas of agriculture and the creation of fish breeding lakes.

Conclusions
The Dammam water specifications conform to the specifications of water suitable for irrigation. The reservoir suffers from an over-exhaustion of groundwater resources because of use in lakes fish breeding.
A significant decline in values hydraulic specification transmissivity and specific capacity of the Dammam aquifer. Through the observation of the monitoring well (W/ 7), a clear reduction and decrease in groundwater levels of flowing wells in the study area.

Recommendations
The researcher recommends closure of the flowing wells that drilled without observing the groundwater investment controls. Backfilling of the random fish breeding lakes because causes the exhaustion of groundwater resources.
Recycle and reuse water used in fish breeding lakes and irrigation. Establishing regulations and laws to preserve the groundwater reserves and holding accountable those who do not abide by them.