Hydrochemical Evaluation of Groundwater from Selected Wells in Al Muthana Governorate, Southern Iraq

The study area is part of the city of Samawa in Al Muthanna Governorate in southern Iraq. The study area is located to the west of Samawa city bounded by the north latitudes 31011-3142 and east longitudes 445845016and its groundwater resources are developed for supply and irrigation purposes. In order to evaluate the quality of groundwater in the study area, twenty three groundwater samples were collected and analyzed for physical and chemical parameters. Hydrochemical analysis showed that the groundwater of the study area is excessively mineralized and very hard. The increase in flow length of groundwater in the study area caused a change in water quality from bicarbonate to sulfate and chloride. The abundance of the major ions is as follows: SO4> CL>HCO3>NO3and Na>Ca>Mg>K. The dominant type of groundwater is Na + sulfate. The water of the studied wells is not suitable for human drinking. Depending on TDS and EC values, most samples of the water are moderate saline class for irrigation. Most wells are good to permissible (wells No.4,14,17) and doubtful (well No. 12) for irrigation depending on Na%, while unsuitable for irrigation depending on EC (except well No. 17 which is permissible). Excellent water class (S1)for agriculture was recorded depending on SAR, except for well N0.2 which had an a good class (S2).


1: Introduction
The hydrogeological studies are considered as an important task in regions where groundwater is the only source of water , which is used for various purposes, particularly in agriculture .Therefore, the decline in the quality of groundwater occurs as a result of increasing salinity in the soil .The objectives of this research are: a-studying the hydro chemical properties of groundwater, bdetermination of the quality of groundwater, c-determination of the validity of groundwater for different uses by comparing with the Iraqi and global specifications.

1-1: Study Area
The study area is located to the southern part of Iraq within Al Muthana governorate to the west of the city of Samawa and to the south of Sawa Lake, bounded by the north latitudes 31⁰11'-31⁰42' and east longitudes 44⁰58'-45⁰16'(Figure -1).The study area and the surroundings are entirely covered by sedimentary rocks of Cenozoic Era, ranging in age from Early Eocene up to recent Quaternary sediment.Lithologically, the following stratigraphic sequence exists: Figure 1-Geological map of the study area [1] 1-Rus formation (Early Eocene): The Rus formation corresponds to beds previously assigned to the Dammam formation [2].It comprises recrystallized limestone, which is partly silicified.In the Mesopotamian zone of south Iraq, the formation consists predominantly of anhydrite with some unfossiliferous limestone, blue shale and marl [3].The formation is not exposed in the study area.2-Dammam formation (Middle-Late Eocene):It is the only exposed formation of paleogene Epoch in the study area.It is comprised of limestone, dolomite, marl, and shale.Dammam formation is deposited in the carbonate inner shelf lagoon and shoal [2].

3-Euphrates formation (Early Miocene):
The formation is composed of shelly, chalky, well bedded, recrystallized limestone [4].The geological conditions of this formation, represented by the abundance of openings and interstitial spaces as a result of the dissolution of limestone, contributed to the formation of this reservoir as an important groundwater reservoir.4-Nafayil formation (Middle Miocene) : The section of Nafayil formation is of a composite type.The lower member is in Garat Nafayil south of Haditha, whereas the upper member is exposed at 3km to the west of Al-Habbania lake.The lower member of Nafayil formation is exposed in the study area in a limited location, forming Mesas and small spots that overly Euphrates formation to the east of Sawa Lake.Only the lower member of the Nafayil formation, which consists of cyclic deposits, is exposed in the study area.5-Quaternary sediments: The quaternary deposits consist of the sediments of the plaiostocene and the Holocene.These deposits cover the study area, which are marine, river and air sediments, and their thickness ranges between 140-200 meters.These sediments are characterized by their high permeability that helps to filter surface water to the underground layers that can be reservoirs of groundwater.

1-2: Materials and Methods
The physical and chemical data for twenty three wells in Samawaharea(Figure- ) as well as hydrogen ion concentration(PH), electrical conductivity (EC), and total dissolved solids(TDS)(Table -2).The samples of water were collected in September 2014 (water deficit period).The samples were placed in plastic bottles with a volume of 1.5 liter after washing by distilled water and then rinsed by sample water for each well to ensure the elimination of pollutants.pH and EC were measured in the site after collecting the samples using calibrated EC-pH meter with a standard solution, while TDS was measured by the evaporation method.Water samples were analyzed to determine ions concentration in the laboratories of General Commission for Groundwater.

2-1: Physical Parameters
Hydrogen ion concentration (PH): It is the reciprocal of the logarithm (base 10) of the hydrogen ion concentration in moles per liter .pH is one of the most important operational quality parameters of water [5].Neutral water has a pH value of 7.0 , alkaline water is more than 7.0 and acidic water has less than 7.0 .Most groundwater has pH values between 5.0-8.0 but it is usually in the range of 6.5-8.5 [6].pH value in the water of study area ranged between 7.1-7.81with a mean value of 7.3.Most wells were weakly alkaline 7.2-7.6.Electrical conductivity (EC):It is the ability of 1cm 3 water to conduct an electric current at a standard temperature of 25C • and measured in micro Siemens per centimeter (µ.s\ cm), depending on the total amount of soluble salts [7].The variation of conductivity gives important information about the evolution of water quality.EC represents a good evidence to determine the mineralization degree of water [8].The EC values in groundwater of the study area ranged between 1307-17550 µ.s\cm with a mean value of 6664 µ.s\cm.Water samples are classified as being of excessively mineralized water (Table - Total Dissolved Solids (TDS): It is a measure of the total amount of minerals dissolved in water and is a very good parameter in the evaluation of water quality [9], also reflecting salinity [10].It is measured by parts per million (ppm) or milligrams per liter (mg\L) units.The TDS values in the groundwater of the study area ranged between 1290-14244 ppm with a mean of 5188 ppm.TDS content of groundwater may increase by movement of water through rocks containing soluble minerals matter, while it is concentrated by evaporation [11].
Total hardness (TH): Hardness of water is a measure of the capacity for precipitating soup.The primary components of hardness are calcium and magnesium.Hardness is measured by ppm or mg/l units according to the following equation: [12] where Ca +2 and Mg +2 are the concentrations of ions in ppm.Water is classified into several types according to its total hardness, as in Table 4. Very hard Very hard 300<TH TH values in the study area ranged between 680-2939ppm with a mean value of 1679ppm , which indicates that all samples are of very hard water.

2-2: Chemical Analysis
Calcium ion (Ca +2 ): Subsurface water in contact with sedimentary rocks derives most of their calcium from calcite, aragonite, dolomite, anhydrite, and gypsum [15].Some calcium carbonate is desirable for domestic water because it provides liner in the pipes, which protects them against corrosion [16].Sewage water contains a large quantity of organic materials which, when oxidized, release quantities of CO 2 , leading to an increase of Ca +2 [17].Calcium concentration in water samples of the study area ranged between 129-802 ppm with a mean value of 373ppm.Magnesium Mg +2: The common sources of magnesium in the hydrosphere are dolomite in sedimentary rocks; olivine, biotite, hornblende, and augite in igneous rocks; and serpentine, talc, diopside, and tremolite in metamorphic rocks.Magnesium is found in lower concentrations than calcium in natural water due to slow dissolution of dolomite together with the greater abundance of calcium in the earth's crust [15].Magnesium ions concentration in groundwater of the study area ranged between 87-373 ppm, with a mean value of 181ppm.Sodium Na + : Sodium is the most abundant among the alkali elements, and makes up 2.6% of the earth's crust being the sixth most abundant element over all.The essential source of most sodium in natural water is from the release of dissolvable products during the weathering of plagioclase and feldspars.In areas of evaporatation deposits, the dissolve of halite is also important.Clay minerals may, under proven conditions, release large quantities of commutable sodium [18].Sodium is a significant factor in assessing water for irrigation and plant watering, where high levels affect soil structure and the plant's ability to take up water [19].Sodium concentration is important in classifying irrigation water, because sodium reacts with soil to reduce its permeability [13].Sodium concentration the in study area ranged between 133-1384 ppm with a mean value of 633.5 ppm.Potassium K + : Clay minerals, feldspar, and mica are the main sources of potassium ions, along with evaporates containing highly soluble sylvite in some sedimentary rocks.The concentration of potassium ions is less than the concentration of sodium ions in groundwater, with the reason being the lower solubility of sodium ion [20].Potassium ion increases in groundwater due to the use of chemical fertilizers [21].Potassium plays an important role in plant growth.In every liter of human blood, there is 180-220 mg /L of potassium, and the lack of this amount, as well as increasing it, causes disturbance in the body [5].Potassium concentration in water samples of the study area ranged between 6-120 ppm with a mean value of 61.7 ppm.High concentration of potassium in some samples of the study areais due to the effect of agricultural fertilizers.Chloride CL -: Chloride is a minor constituent of the earth's crust, but a major dissolved constituent of most natural water.It represents an important element in the hydrologic cycle, where its content in rain water is usually less than 10 ppm, whereas in groundwater it varies from few ppm in the snow-fed wells to high content in desert brines.Chloride ion is available in evaporated rocks and in rock minerals such as apatite and soda [22].In addition, the treatment of water with chloride can lead to increased concentrations in the groundwater [5].Chloride concentration in the water samples of the study area ranged between 242-2202 ppm with a mean value of 836 ppm.High chloride concentration in groundwater of the study area may be an indicator to pollution by sewage and agriculture fertilizers.* Sulfate (SO 4 -2 ): Sedimentary rocks such as gypsum and anhydrite represent an important source of sulfate [13], while other sources are agricultural and industrial activities [23].Sulfate concentration in the water samples of the study area ranged between 439-2285 ppm with a mean value of 1321 ppm.All water wells of the study area do not meet with the standard concentration of IQS 2009 [24] (400 ppm) and WHO 2007 [25](250 ppm).Bicarbonate( HCO 3 -): The primary source of bicarbonate ion in groundwater is the melting of calcareous rocks in water, which contain the dissolved carbon dioxide of dissolved carbon, as well as the presence of hydrogen ion resulting from the dissolution of carbonic acid.Decay of organic matter may also release carbon dioxide for dissolution [26].The concentrations of bicarbonate in the study area ranged between 68-1342ppm with a mean of 582 ppm.Nitrate (NO 3 -): Organic matters and fertilizers represent the most common sources of nitrates in natural water; they originate from industrial and agricultural activities [27], [28].Nitrate has a direct effect on plant growth and may cause a hazard for drinking water sources if the levels reach to 10 ppm or higher [29].Nitrate concentration in the study area ranged between 1.2-12ppm with a mean value of 4.9ppm.Nitrate concentrations in the study area are lower than the standards values of IQS 2009 [24]and WHO 2007 [25] (50 ppm for both guidelines).

2-3 Water types and hydro chemical formula:
Types of water are connected to the chemical and physical properties, which change relatively with respect to time and space.These changes are slow in groundwater compared with surface water [30].Water type is very important to determine its suitability for the different uses (human, agricultural, and industrial purposes).Many classifications depend on the concentrations of main cations and anions by unit equivalent weight of ion (epm)  or milli equivalent per liter (meq / l).The hydrochemical formula is defined as an equivalent weight ratio for all ions having a ratio of higher than 15% in groundwater, which are arranged regularly according to the concentration of each ion, in addition to TDS and pH values.The result of this formula determines the water type .The formula (also called Kurlolov formula) was taken from Ivanov 1968 [31] is: shows the type of groundwater in the studied area, as resulted from the use of the hydrochemical formula.It is an important measure in geochemical reactions through the flow of groundwater, where the increase in flow length will change the water quality from bicarbonate to sulfate and chloride.This could be an indicator to the length of groundwater flow [32].We note from the results that most wells are of a sulfate water type.
One of the important classifications of the irrigation water depends on the salinity (EC&TDS) [33] as shown in .Comparing with this standard, the groundwater samples of the study area are moderate saline .Residual sodium carbonate (RSC): A high concentration of bicarbonate in irrigation water may lead to the precipitation of calcium and magnesium in the soil and thus to a relative increase of sodium concentration.Therefore, the sodium hazard will increase [34].The bicarbonate hazard is expressed by RSC which was introduced by Eaton, 1950 [35], as follows: ).Where all ions are measured by the equivalent weight (epm) .RSC values in the study area ranged between -65.5 to -11 epm with a mean of -24.2.According to the classification of Eaton, 1950,[35] (Table 9), all the samples of groundwater in the study area are safe for irrigation.(Eaton, 1950) [35] RSC (epm) Water type Area study <1. 25 Safe All samples( negative values) 1.25-2.5Marginal >2. 5 Unsuitable Soluble sodium percentage (Na %) and EC: Sodium content is commonly expressed in terms of sodium percentage.Increasing sodium ion ratio in irrigation water will affect soil efficiency, where it leads to a decrease in its porosity and permeability, and thus will affect the plant growth or stunted growth.Na% value is calculated according to the following equation: ] Where all ionic concentrations (rNa, rK, rCa, rMg) are expressed in epm Na% values in the study area ranged between 23-62.5 with a mean of 44.6.The classification of Tood ,1980 [12], for irrigation water based on Na% and EC values (Table -7) was adopted in this study, while the results of this study are explained in Table-10.Sodium adsorption ratio (SAR): The two most common water quality factors that influence the normal rate of infiltration are the salinity of water and the relative concentrations of sodium versus magnesium and calcium ions in the water, known as the SAR.It is an important parameter for determining the suitability of water for agriculture, because it is a measure of alkali /sodium hazard [36].Karanth, 2008[37], defines SAR of water as:

{√( )
where Na + , Ca +2 and Mg +2 are concentrations of ions in epm units.High values of SAR imply a hazard of sodium replacing absorbed calcium and magnesium , a situation that is ultimately damaging to soil structure [22].There are four classes of water for agriculture depending on SAR value according to Subramain ,2005[36].All samples in the study area had a SAR value that is lower than 10 except sample No.2 (10.8),whereas the range was between 2.2-10.8epm and the mean was 6.6epm.These results indicate an excellent water class(S1) for agriculture .it seems that the current groundwater for all studied wells is suitable to use for livestock purposes ,but the degree of suitability is different from well to another, ranging between very good to acceptable for use according to Altoviski 1962[38] classification.2-4-4 Water suitability for industrial purposes: Water samples for the study area were determined for industrial purposes by using Hem(1985) [22] classification (Table-13).

Table 1 -
Groundwater samples and their coordinates

Table 2 -
Physical and chemical values for water samples in the study area

Table 4 -
Classification of water according to Total hardness

Table 5 -
Chemical analysis of groundwater samples in epm units.

Table 8 -
classification of water for irrigation and agriculture purposes

Table 9 -
Classification of irrigation water based on RSC values

Table 10 -
[12]results according to the classification of Todd (1980)[12]for irrigation water based on Na % and EC.