Iraqi

Groundwater is an important resource that can be used for various purposes. Various factors can change the chemistry of the GW, such as the chemical composition of an aquifer as well as the leaching of human waste into groundwater. The study area is a barren land covered by some sabkhas, in addition to some agricultural fields. The study aims to assess groundwater quality for drinking purposes using the Water Quality Index. The groundwater is chemically heterogeneous and has a wide quality range from very poor to excellent. Evaporation appears to be the controlling factor among the other shallow waters, while relatively deep water is related to rock-soil dominance. Rocks, land use and land cover have helped control the groundwater quality. Moreover, the heavy use of fertilizers, pesticides and irrigation, in addition to the presence of sabkhas, contributed to the deterioration of the groundwater quality. The water-rock interaction and evaporation are the dominant mechanisms that are controlling the groundwater quality in the study area.


Introduction
The study of groundwater quality (GWQ) is extremely important. The exploitation and deterioration of GWQ are the main reasons to continue conducting studies over the world. Many physical, chemical and biological processes affect the properties of the groundwater (GW), such as decomposition of organic matter, iron reduction, precipitation, ion exchange, and dissolution during the movement of GW (Kumar et al., 2014;Machiwal and Jha, 2015;Mohapatra et al., 2011). The result of pollutants induced by human activity and anthropogenic pollutant sources are additional factors of GWQ deterioration (Gnanachandrasamy et al., 2020;Venkatramanan et al., 2016). The deterioration of GW is due to uncontrolled use of agricultural pesticides, fertilizers, soil amendments, leaching the domestic, and industrial wastes to the water table (Rao, 2014;Al-Hamadani et al., 2016). In agricultural areas, the hydrodynamic properties of GWusually change due to the existence of a link between surface water, irrigation water, and GW (Hui et al., 2020). Various factors control the GWQ and suitability for different purposes as it is affected by interactions between water, rocks or soil, agricultural fertilizers, pesticides, anthropogenic activities, runoff and infiltration system, industrial waste, rainfall, evaporation, and topography (Karunanidhi et al., 2020;Mahmud et al., 2020). Any increase in the concentration of chemical elements, i.e., major cations, anions, and heavy metals, will induce GW pollution and deteriorate the GWQ (Zhang et al., 2020;Al-Jaberi et al., 2016).
Usually, GW is often classified and clarified for the main hydro-geochemical characteristics through the use of the Piper diagram, which is one of the most suitable tools for this purpose (Gnanachandrasamy et al., 2020;Kumar et al., 2014;Rekha et al., 2013;Awadh and Ahmed, 2013;Todd and Mays, 2004). Three main mechanisms control the chemistry of GW; precipitation, rock dominance, and the process of evaporation fractional crystallization (Gibbs, 1970). The GW and aquifer lithology's reaction plays an important role in assessing the WQ (Gnanachandrasamy et al., 2020;Rao, 2006;Yenugu et al., 2020). The WQI was initially found by Brown et al., (1970), developed by the National Sanitation Foundation (NSF) (McClelland, 1974) and later modified by Backman et al., (1998). It is a simplified and specific quantitative method for measuring the WQ. The application of WQI helps the decision-makers in the possibility of successful management of WQ and supplied more details about the WQ for various uses by public people (Yenugu et al.,, 2020). It is an integrated classification technique to define the effect of some chemical elements' standards into a single valuable value that summarizes water quality Bhuiyan et al., 2016;Rawat et al., 2018;Vasanthavigar et al., 2010;Yenugu et al., 2020). The WQI can also be used as a tool that grouped the hydro-geochemical parameters as a reference to give integrated information on the GWQ (Gnanachandrasamy et al., 2020). The geographical information system (GIS) technique can be integrated with WQI for mapping the GWQ (Gharbia et al., 2016;Hasan and Rai, 2020). This work has been carried out on the unconfined aquifer in the Rashidiya region. The dominant activity in the area is the agriculture of seasonal crops and orchards, having many fertilizers, stimulants and agricultural pesticides that all are acting for the deterioration of the GWQ. In the rural areas, many people are insensible to GW pollution; particularly, the GW wells are not subjected to continuous monitoring of WQ. The main information that is used in this study is based on field surveying, Land use/land cover (LULC), interpretation of the chemistry of the GW. The present work aims to evaluate the GWQ, distribution of chemical facies together with mapping of the GWQ using GIS and an illustration of the controlling mechanism of the GWQ.

The Study Area Location and Description
The study area is located in Rashidiya, north of Baghdad, bounded by the latitude (33̊ 24 '00 " and 33" 36 "30") N, and longitudes (44 "18" 00 "and 44" 24 "25") E (Fig. 1). The study area is a part of the alluvial plain located to the east of the Tigris River. The river levee soil and river basin soil-silted phase are the main alluvial soil that covered the study area. The river levee soil consists mainly of a relatively coarse texture layer of fine sand to silty clay loam and the texture becomes finer with depth. The wells' depth is not exceeded (54 m) and the water table is fluctuated between (6.5 to 14.5 m) from the surface according to the amount of Tigris River discharge and elevation. The covered soil is well-drained, and excess water drains to the river. The river basin soil consists of silty clay loam, silty clay, and clay with 50 to 70% of clay containing high calcite grains, so it is characterized by poorly drained with the high water table and fair to very poor soil with high to strongly saline (Buringh, 1960).

Area Category
The spatial variation of the WQ for drinking purposes in the study area is need data of GW chemistry, LULC, soil type, and agriculture activities. The GW samples were collected from an area extended to about 257 km 2 . The LULC map was prepared from the Sentinal-2 satellite, collected on 18th Nov 2019. The classification was carried out using ENVI v 5.3 software. The training data of 6 LULC types were selected and verified in the field. The supervised classification algorithm, i.e., Spectral Angle Mapper (SAM) was also applied. Barren lands occupying about 32.3% have been identified. They are used for seasonal crops, to which intensive fertilizers are added in surplus quantities. The building area covers about 31.6%, representing cities and villages with some dispersed population around. The orchard fields cover about 31.1%, requiring intensive irrigation, more fertilizers, and pesticides, while wheat crops account for about 2.2%. The Tigris River's wetlands are covered of about 1.5%, and the remaining parts represent the water bodies that occupy about 2.2%.

GW Sampling
Thirty samples of GW were collected from the shallow aquifer in the study area on 18, 20, and 21 st Dec 2019. Samples were collected by using polyethylene bottles of 1L capacity after preliminary pumping around 10 min. The GW wells were selected to represent the study area, well depth ranges from 10 to 54 m. The sample sites were documented by using the Global Positioning System (GPS).

Chemical analysis of GW
Chemical analysis of GW was carried out using several analysis methods as given in Table 1. The samples were analyzed in the Ministry of Science and Technology Labs. The error of balance is checked after converting the mg/l to meq/l (Todd and Mays, 2004), and then was checked according to equation 1 (Freeze and Cherry, 1979;Fritz, 1994). (1) The percentage of error must not exceed (5%) to be accepted (Fritz, 1994). Otherwise, the results are not reliable (Todd and Mays, 2004). The error rate indicates high reliability.

Water chemistry and hydrochemical facies and controlling mechanisms
The GW types and hydrochemical facies were assessed based on the Piper diagram using AquaChem V.9 software, while the mechanism that affected the GW composition was identified according to Gibb's diagrams using GraphPad Prism 5 software. The plotting of Gibbs ratios of cations and anions against the total dissolved solids (TDS), predicts the mechanisms controlling the source of chemical constituents of GW. There are two Gibb's ratios computed according to equations 2 and 3 (Gibbs, 1970;Gnanachandrasamy et al., 2020;Kumar et al., 2014;Kumar et al., 2009).

Water quality index (WQI)
The computing of the WQI requires weighting the chemical variables based on their relative importance in the overall quality of water for drinking purposes (Abbasnia et al., 2018;Kumar et al., 2014). Relative weights are calculated according to the weight given in Table 2 (Bhuiyan et al., 2016;Vasanthavigar et al., 2010) using the equation 4.
= / ∑ =1 (4) Where Wi is the weight of i th parameter, wi is the relative weight of i th parameter and n is the number of parameters. The ratio of parameter concentration in water samples (Ci) to the World health organization (WHO) standard of the parameter (Si) assigned as quality rating index (qi) of i th parameter which is computed according to the following equation 5.
= × 100 The sub-index of each parameter (SIi) is computed by multiplying of quality rating index (qi) by the relative weight (Wi) of each parameter, as given in equation 6. = × (6) The summation of SIi of all parameters; represents the value of WQI as in equation (7).

Water Chemistry and Hydrochemical Facies
The chemical results of GW in mg/l and meq/l are presented in Tables 4 and 5, respectively. The results of Piper diagrams show six types of water (Figs. 2 and 3a). The water types are mainly controlled by cations (Ca, Mg, Na) and anions (Cl and SO4). Meanwhile, three hydrochemical facies were identified on Piper diagram; in terms of cations, two facies were identified. Alkalis exceed alkaline earths including samples (ws2, ws3, ws4, ws6, ws14, ws15, ws17, ws21, ws22, ws29), whereas, the other samples are of alkaline earths (Ca, Mg) exceed alkalis (Na, K). Based on Anions, all the water samples come in the facies of strong acids (SO4, Cl) exceed weak acids (HCO3). This could be attributed to the infiltrating of the saline water from sabkha and irrigation waters to the water table. The source of GW chemistry was recognized based on Gibb's diagrams (Fig. 4). The analysis of charts was obtained by plotting Gibb's ratio of anions against TDS. Fig. 4a identified the chemical compositions of nine GW samples (ws2, ws7, ws8, ws9, ws13, ws14, ws19, ws21, and ws29) are attributed to the soil-rock dominance as shown in Fig. 3b. These samples (soil-rock dominance) are mostly collected from wells with a depth ranges from 19-54 m, while the rest of the samples (evaporation dominance) are collected from wells with depth ranging from 12-18 m. The process of evaporation-precipitation is recommended to be reported to interpret the factor controlling the GWQ (Awadh et al.,206). The composition of other samples comes from evaporation-precipitation dominance because they are located in highly permeable soils. Based on Gibb's -II ratios of anions against TDS (Fig. 4b). The GW wells (ws3,ws4,ws5,ws6,ws15,ws22,ws23,and ws24) are affected by the evaporation dominance, while the others are affected by the rock-soil dominance (Fig. 3c). The Box and Whisker plot has presented the ranges of the chemical concentration of GW parameters shows that iron, and copper have high variations in their minimum and maximum values as well as potassium (Fig. 5). The extreme concentrations can be seen in Na, Ca, K and SO4 reflecting high variation and heterogeneity.

Water Quality Index
The WQ sub-index (SIi) of elements, WQI, and the GWQ are presented in Tables 6 and 7. The WQI was classified the GWQ for drinking purposes as only NO3, HCO3, Fe, and B are within the permissible (0.12-2.1, 19-582, 0.0011-0.1344 and 0.01-0.09) mg/l, respectively. The EC values in most GW samples are higher than the maximum contaminant level, with values ranging from 1353 to 8770 except the samples (ws13, ws7, and ws8) within the permissible limit (PL) with values of 510, 810, and 825 respectively. The results of WQI are summarized in the GWQ in an integrative and easy way without the need for the standard details of the chemical elements in their individual status. The only sample ws13 was classified as an excellent type located in the northern east part of the study area near the population center. The samples (ws1, ws7, ws8, ws9, ws19, ws20, ws25, and ws27) are classified as good water located in the middle and northern part of the study area. Most wells are located in river levee soil, having well drain with sandy to silty texture.The Poor water types are dominant over most of the study area, including the samples (ws2, ws3, ws4, ws11, ws14, ws18, ws21, ws22, ws26, ws28, ws29, and ws30), despite these samples are collected from wells located in the river levee soil type that is characterized by good drain as the Tigris River recharges the (GW). However, the area is covered by LU of the orchard (Different types of fruits, date palm trees) with intensive use of fertilizers, pesticides, and irrigation processes along the year seasons. The samples collected from bore wells in the middle and east parts are designated as very poor water because the soils of the area are poorly drained, moist soil with high salinity and bits of accumulated water are common, and the sample ws24 was classified as unsuitable for drinking purpose (Fig.6).

Conclusions
The study found that the adoption of international standards for each element or specific factor separately and the WQ classification is flawed by deficiencies. The results showed the validity of water in one component and its unfitness in another. The study proved that applying the WQ standard for drinking or irrigation purposes is more accurate and realistic by adopting the results of the WQ for drinking purposes WQI compared to the standards adopted for each component or parameter separately.
The GW wells are varied in their suitability for drinking purposes based on WQI results; only one water sample collected from well located in northern east part of study was classified as excellent water, whereas, the western part of the study area and near Tigris River were classified as good water for drinking purposes. Most of study area is classified as poor water and a significant area to the west of river classified as very poor to unsuitable. The land use and absence of effective drainage network are the main reason of GW degradation in most of study area. The water-rock interaction and evaporation are the dominant mechanisms that are controlling the GWQ in the study area.