In recent time, there has been a tremendous increase in demand for groundwater in the studied area due to the population grow and intense agricultural activities. The irrigation-water supply in Al-Rasheedia and Guba area is almost entirely based on groundwater. Many deep wells have been constructed for the supply of irrigation water. Very useful hydrogeological data, such as lithological units of deep well, water level depth and geological prospecting, were obtained. Geological and agricultural consumers are supplied with water from aquifers, 70 to 110 meter deep. These aquifers consist of the flat lying Quaternary deposits which cover and extend over the region with thickness of 1-3 meters and Al-Fatha Formation of more than 150 meters in thickness and forms the only sources of ground water in the area. The quality of groundwater is not uniform and differs from season to another due to the difference in rainfall quantity, recharge, fluctuation change of water level and dissolution between ground water and lithological materials such as gypsum. Rainfall is the main sources of recharging the ground water of the studied area. Different factors affect recharge precipitation, among of these are elevation, time, type and intensity of rainfall. The amount of precipitation increase with altitude. Short and heavy rainfalls are directly affect the recharge in the area due to the high permeable soil covered. The depth to the ground water level of deep wells in the studied area range between 6-10 meter during rainy season, while in dry season range between 10-14meter. People in the studied area abstracted water from deep wells to meet their needs and domestic purposes. It is not an exaggeration that the number of wells drilled during the last five years is more than the number of wells drilled in the studied area since its existence. The author has referred several aspects of chemical data and discussed the principle characteristics of ground water quality classifications for domestics and irrigation purposes [1-10].

Location and Description of Study Area

The study area is situated in the north western part of Mosul city and located approximately between latitude 36°  23?  48?– 36°  26? 00? and longitude 43°  02?  15? – 43°  07°  20? . It covers an area of about 90 km² with its elevation varying from 250 - 220 m above sea level Figure (1). The climate is considered to be semi-arid and the annual precipitation being approximately between (280-360) mm. 90% of the total rainfall occurs from Oct - April. The area is characterized by well-developed dendritic type of drainage system. Tributaries are consider to be non-perennial, as it carries water during rainy season and rainfall of high intensity and long duration. Coarse textured patterns noticed in the plains indicating high rainfall infiltration. The regional slope of the studied area is towards the south where the Tigris River. The most important activity of the area is agriculture, and the chief crops are wheat, barley and vegetable.

Figure 1: The study area and well location.

Samples Collection and Analysis

Groundwater samples were collected from (15) deep wells during Oct 2022. The chemical analysis were carried out in the laboratories of the Department of environmental technology in Mosul University according to the methods adopted by the US Geol Survey [11]. Electrical conductivity (Ec) and pH were measured immediately after sampling. Groundwater samples collected in the field were analyzed for major cations (Ca, Mg, Na, and K) and major anions (HCO3, SO4, Cl, NO3), total hardness (TH) and total dissolved solids (TDS). All measurements and major ion analysis are presented in table (1).

Geology setting

Strati graphically, the area under research is dominated by geological formations ranging from Middle Miocene to Quaternary as follows

Al Fatha Formation of Middle Miocene: This formation is cropped out on the hilly region to the North-East of the studied area and composed of alternating layers of gypsum, anhydrite, marl, clay, green marl and lime stone [12,13].

Quaternary sediments: The Quaternary sediments are mostly covering the total area under study. This sediments include residual soil (sandy and loamy soil) and flood plain deposits which consist of sand, silt and clay, and slope deposits which consist of rock fragments, sand and silt which is slightly cemented. The thickness varies greatly from less than 2 m. to over 5 m. The Quaternary sediments and lithological variation of Al-Fatha Formation is illustrated using the geological logs of selected wells drilled by ground water company in Mosul city in the study area as shown in Figure (2).

Figure 2: Litho-Log of selected wells of the study area.

Table 1: Concentration of chemical constituents of ground water samples (ppm).

Table 2: Chemical parameters of ground water samples.

Hydrogeology Setting

The hydrogeology of the study area is interpreted on the basis of the available documentary evidence and records such as bore hole lithology and geology.

• Unconfined aquifer, mainly in the Quaternary sediments which has wide geographical distribution and of thickness ranges from 3 to 6 m. This aquifer is underlined by the Pliocene clay which act as a confining bed. The main source of recharge to this aquifer takes place from direct rainfall and wadis runoff.
• Al-Fatha formation is considered to be a semi confined aquifers. Bore hole lithology records as shown in figure (2). Reveal that the formation is separated from Quaternary sediments by an aquiclude of clay sediments in some places, and are hydraulically connected with Quaternary sediments in others. This aquifer consist mainly of variable lithological units of permeable and impermeable beds and receives its water mainly by underflow and leakage from upper regional aquifer. This aquifer is well jointed and fissured and in local scale exhibits solution channels.

Rainfall is the main source of aquifer recharge. It occurs along Quaternary sediments. In addition, infiltration from intermittent tributaries that drain water during period of heavy precipitation.

Hydrochemistry

The dissimilar composition of ground water type result from numerous hydro chemical processes, among of these processes is the interaction between ground water and host rocks. The concentration of dissolved ions in ground water samples are generally governed by lithology, velocity and quantity of ground water flow, nature of geochemical reactions, solubility of salts and human activities [14,15].The total dissolved solids (TDS) of ground water analysis is found on the higher side level by comparing with the specification of (TDS) values set up by the[16]. The excess of TDS in the analysis is caused by mixing of surface pollutants during the infiltration and percolation of rainwater downward and the interaction between the groundwater and host rocks.

The electrical conductivity (Ec) make a sign of the amount of salts dissolved in water and its value of ground water samples range from 980 mmhos to 1420 mmhos.

The pH value of ground water samples in the study area fluctuate within the narrow limits between 7.07 and 7.45.

Sodium Percentage (Na%)

Sodium concentration is important in classifying irrigation water because sodium reacts with soil to reduce its permeability. Sodium content is usually expressed in terms of percent sodium (Na%). The Na% values of ground water samples range from 29.37 to 46.07. The sodium percentage (Na%) is calculated using the following formula: Na% = (Na + K)* 100/(Ca+Mg+Na+K). Where all the concentration are expressed in meq/l.

The Na% of samples (2, 3, 4, 5, 9, 10, 11, 12, 13) indicates that the ground water is good for irrigation while samples (1, 6, 7, 8, 14, 15) are permissible [17].

Sodium Adsorption Ratio (SAR)

SAR is an important parameter for determining the suitability of ground water for irrigation because it is a measure of alkali/ sodioum hazaed to crops. The SAR can be estimated by the formula:

SAR = Na/sqrt(Ca + Mg)/2

Where all ionic concentration expressed in epm.

The SAR value of ground water samples range from 2.88 to 6.82 which is fell in the low sodium class. This implies that no alkali hazard to the crops [18].

Residual Sodium Carbonate (RSC)

The excess sum of carbonate and bicarbonate in ground water over the sum of calcium and magnesium also influence the unsuitability of ground water for irrigation. This is denoted residual sodium carbonate (RSC), which is determined by the formula [17].

RSC = (HCO3 + CO3) – (Ca + Mg)

Where the concentration of cations and anions are expressed in epm.

From the residual sodium carbonate value of the ground water samples of the study area, it is observed that all samples are safe for irrigation according to the US Salinity Laboratory Diagram [9], which is proposed that water containing less than 1.25 meq/l is safe for irrigation.

Permeability Index (PI)

The soil permeability is influenced by Na, Ca, and Mg and HCO3 contents of the soil and affected by long term use of irrigation water. It is defined as follows [17].

PI = (Na + sqrt HCO3)*100/(Ca + Mg + Na )

Where the concentration of cations and anions are expressed in epm.

The value of PI of ground water samples of the study area range 32.3 to 46.7 which comes under class II ( 25-75% ) of  Doneen chart (Domenico and Schwartz), therefore the ground water sample in the study area is in general suitable for irrigation purposes on the basis of US Salinity Diagram [19].

Hydro chemical Faces

The geochemical classification of ground water can be understood by using Piper diagram. In the proposed diagram Figure (3), the Results of analysis of groundwater samples Table (1) were plotted on the proposed diagram to test its applicability for geochemical classification. Samples (1,2,3,4,5) fall under the subdivision of water type (5) while other samples fall under the subdivision of water type (3).Stiff diagrams are commonly used for displaying major ion composition of groundwaters and it is  useful in the analysis of groundwater ion concentration. It can be used to help visualize ionically related waters from which a flow path can be determined and show how the ionic composition of a water body changes over space or time. A typical Stiff diagram is shown in the figure (4).

Figure 3: Piper Diagram.

Figure 4: Stiff Diagram.

Irrigation water quality

The Richard classification diagrams [20], has been used Figure (5) to identify the availability of ground waters for irrigation use. This graph is based on the electrical conductivity (Ec) and sodium adsorption ratio (SAR), where Ec is a good measure of salinity hazard to crops and SAR is a measure of alkali/sodium hazard to crops. According to this graph ground water samples (4, 10) fall in the field of C3-S1 indicating high salinity and low sodium water, which can be used for irrigation on almost all types of soil. Samples (2, 3, 5, 9, 11, 12, 13) fall in the field of C4-S1, indicating very high salinity and low alkalinity hazard. This can be suitable for plants having good salt tolerance. Samples (1, 6, 8, 14, 15) fall in the field of C4-S2 indicating very high salinity and medium sodium which is not suitable for irrigation under ordinary conditions but may be used under very special circumstances.

Figure 5: Richard classification of groundwater samples.

The varied chemical composition of abstracted ground water in the studied area is a manifestation of the genetic association between the ground water and the host rocks that contain it. It is very important to determine the source of contamination in order to protect the groundwater. The present study demonstrated the importance of constructing graphical representations, such as Piper trilinear diagram plot using dissolved constituents (major cations and major anions) to effectively understand hydro chemical evolution, grouping and areal distribution of water faces of groundwater resources of Rasheedia and Guba area. Samples (1, 2 ,3,4,5) fall under the subdivision of water type (5) while other samples fall under the subdivision of water type (3).

The ground water of the study area based on TDS, SAR, Na% and PI are suitable for agricultural purposes, Richard classification revealed that the most dominant classes are C3S1, C4S1 and C4S2 indicating high to very high salinity. Therefore plants with good salts tolerance should be selected. The negative value of chloral alkaline indicates that the host rocks are primary sources of dissolved solids in the water.

The overall quality of ground water of the study area is controlled by natural factors (geological environment), geological relationship, hydrogeological condition and lithology of the aquifers that contain the abstracted ground water. The present work recommends using the Piper trilinear diagram technique widely, to evaluate the quality of groundwater and understand the hydro chemical faces characteristics.

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