Hydrochemistry of Groundwater in Dibdibba Aquifer Between Karbala and Najaf, Centeral Iraq

ABSTRACT


Introduction
The groundwater contains variable concentrations of dissolved chemical elements as well as organic components.That may have negative or positive effects on the water quality for various uses.Water is a solvent dissolving mineral from the rocks which it comes in contact with.
Groundwater investment decisions concentrate frequently on the quantitative side, but the qualitative side is critical since it affects its suitability for various uses (Tood, 2007) and it is also affected by geological layers more than surface water, so it contains a variety of total dissolved substances (Zoran and Adrian, 2008).Groundwater quality means determining special criteria for assessing water's physical, chemical, and biological properties.The most common of these criteria is the quality of drinking water for humans and animals (Nah et al., 2017).There are many previous hydrochemical studies conducted on the current Dibdibba plateau in Karbala and Najaf. Al-Ghanimy (2018) assessed the hydrogeology of the Karbala-Najaf Plateau in Iraq, and the groundwater quality using chemical analyses and physical properties of the aquifers at Dibdibba and Dammam.His findings revealed that the groundwater TDS and EC values increased in accordance with the groundwater's flow direction from west to east.According to TDS values, groundwater samples taken from the Dibdibba aquifer in the research area are classed as brackish type water based on classification systems.
By evaluating the physical, hydraulic, and hydrochemical characteristics of the Dibdibba and Dammam aquifers, Al-Sudani (2018) explained good sites for groundwater exploitation in the Dibdibba aquifer.
However, due to the significant population growth as well as the investment of groundwater for significant agricultural and industrial projects in the study area over the past few years, the study area needs to be periodically monitored and complementary studies in terms of hydrochemical developments and the suitability of water for life uses.The purpose of the study is evaluation and interpretation of the physicochemical and hydro-chemical properties of the Dibdibba aquifer in the study area.

Geological and hydrogeological description
The geological formation in the study area within Tertiary and Quaternary from the middle Eocene to Pleistocene, and they are from oldest to youngest (Dammam, Euphrates, Fatha, Injana, Dibdibba), whose deposits are of the Quaternary Era (Jasim and Goff, 2006) (Fig. 2).The study area is located hydro geologically within the Mesopotamia and western desert zone, within the main aquifers of groundwater of the Miocene carbonate and Mesopotamian Plain silt (Jasim and Goff, 2006).

Hydrochemistry evaluation
The concentrations are in (ppm), then converted to (epm) and (epm%) for use in ionic balance to show the accuracy of the results (Table 3), and in water indicators for irrigation, as well as we mapped the spatial distribution of salinity, electrical conductivity, major ions, minor ions, heavy metals, alkaline and total hardness, then the results are discussed.

Water quality index
The water quality index is calculated according to Cristina et al. (2014) as shown in the equations below (Eq.1, 2, 3, 4).
Where Wi: unit weight, Si: recommended standard for i th parameter, k: proportionality constant Qi: sub-index of i th parameter, vi: monitored value of the i th parameter, v: measured concentrations.

Hydrochemistry analysis results
The analysis results of the major ions, minor ions, salinity and electrical conductivity, water quality index, and indicator of irrigation and the balance of major ions are shown in Tables (3,4).

Spatial distribution maps:
The spatial distribution maps for the total dissolved solids (TDS) and electrical conductivity (EC) are drawn (Fig. 3).Their values increase towards east and southeast of the middle and go down towards west and north.There is a positive relationship between electrical conductivity and total dissolved solids (R 2 = 0.9) (Fig. 4).(Na) and (K) distribution maps (Fig. 5) show that their concentrations increase towards south and middle near the gas and fertilizer plant (BH.10) and the desert palm forests (BH.21).Ca and Mg high concentrations (Fig. 6) are in the southeast of the middle region, while the water hardness goes in the same direction, and its water is classified as very hard according to Sawyer and MaCarty (1985) as ranges between (803-4309) ppm.Cl, SO4 and HCO3 (Fig. 7) increase towards southeast of study area near the place of population as well as agricultural areas.The increase in the concentrations of these ions is often due to geogenic reasons, especially since calcium, magnesium, and bicarbonate ions all increase almost in the same direction.The high concentrations of the minor nitrate ion (NO3) are in the red color (Fig. 8) and their wells (BH-57,15,16) (Fig. 1).The reason for the increase is chemical or organic fertilizers.The concentrations of major and minor ions increase from west to east in the study area; that is, they increase towards the groundwater flow (Al-Qaisi, 2023).

Heavy metals
The results of the heavy metals in the water samples collected from the population area within the study region (Table. 4) show that (Fe, Co, and Cu) concentrations are within the standard permissible limits in all samples, but the concentrations of (Mn) are within the standard permissible limits except (M.w2).Pb is safe in all samples except (M.w10) (very high), but most results of Ni concentrations are high and considered polluted, it is not safe of harmful effect according to the standards of WHO (2017) andIQS (2009).Figure (9) show the spatial distribution for the high concentration of (Ni, Mn).

Water quality classification
The results of the chemical analysis are represented in the Piper chart (Fig. 10).The water samples are within two classes: class (g) (alkaline waters with prevailing sulphates and chlorides) and class (e) (earth alkaline water with an increase portion of alkali with prevailing sulphates and chlorides).In Steve's chart, the water of the study area is classified as anions with prevalent sulphate, except in (6) wells; in 5 of them 24,27,43,42), chloride and sulphate are equal, and in the 6 th well (BH-47) prevailing chloride.On the other side, sodium and potassium are dominant, except in one well  in the middle of the study area, in which magnesium predominates.The study area's groundwater consumption for irrigation is assessed using a number of indicators, including the sodium adsorption rate (SAR), sodium percentage (Na%), Kelly index (KI), and permeability index (PI) in table (3).Additionally, the sources for all of the standards for the aforementioned indicators are shown in table (7).The study area, according to the (SAR) indicator, is excellent for irrigation, and (Na%) is mostly good and intermediate type for irrigation, with the exception of the eastern part of the region, which is not suitable for irrigation due to the high percentage of sodium and potassium, and the (KI) considered it good for irrigation and medium.For irrigation, the (PI) is classified as intermediate.This information is discovered after the spatial distribution of the irrigation indicators in figure (13).

Conclusion
• The potassium ion concentrations in the area are rather high, especially in Najaf Governorate near the fertilizer and gas factory and the desert palm forests, where there is heavy afforestation in the region, while the concentrations of nitrate ion range between (0.2-2.1) ppm to fertilizers chemical or organic, while the values of alkalinity are calculated for the samples of the study area between (154.2-654.4)ppm, which is identical to the bicarbonate ion in the spatial distribution map.
• There is pollution with heavy metals in the study area, especially (Ni, Pb, and Mn) according to the standard specifications of the World Health Organization (WHO, 2017) and the Iraqi Specifications (2009).
• The quality of the water is sulphate, and the reason may be due to the rocks of the Dibdibba reservoir and the covering rock of the area formed by gypcrete derived from the formation itself.
• Most of the wells in the study area are not suitable for human drinking according to the World Health Organization (WHO, 2006).Based on the water quality index (WQI), it is acceptable for animals drinking and unacceptable for poultry.
• Groundwater in the study area cannot enter the food, chemical, cement, paper and refinery industries only after treatment or processing, because it is not suitable in its natural condition, due to the high concentrations of elements.
• The indicators of irrigation sodium adsorption ratio (SAR), the percentage of sodium (Na%), the Kelly index (KI) and the permeability index (PI) were showed that all wells in the study area are suitable for irrigation, but with different specifications and certain percentages after comparing it with standard specifications.

Fig. 2 .
Fig.2 .Geological map of the study area from Iraqi geological map, 1996 Samples collection and analysis Wells are selected from different locations between Karbala and Najaf in the study area for sampling.The samples are filtered with 45-micron paper and acidified with nitric acid.The samples are analyzed by the central laboratory of the University of Tikrit and the laboratory of the General Authority for Ground Water in Baghdad according to the analytical methods and to the references listed in Table (1).

Fig. 5 .
Fig.5 .Concentration spatial distribution maps (ppm) for Na at left, and K at right.

Fig. 6 .
Fig. 6 .Concentration spatial distribution maps (ppm) for Ca at left and Mg at right.

Fig. 9 .
Fig. 9 .Concentration spatial distribution map (ppm) for Ni at left and Mn at right.