Groundwater is an essential part of water resources for drinking, irrigation, and industrial purposes around the world. The groundwater quality could reveal important information on the geological formation of the aquifers and the suitability of groundwater for various purposes (Nagaraju et al., 2016). Generally, the chemical composition of groundwater is controlled by several factors, including hydrogeochemical process, degree of rock weathering, hydrodynamic conditions, residence time, and soil inputs when water infiltrates (Appelo & Postma, 1996). The interaction of these factors results in various hydrogeochemical types of groundwater (Shvartsev, 2008). Therefore, the study of hydrogeochemistry is a useful tool for identifying the origin of the groundwater chemical composition and the process responsible for groundwater chemistry (Singh et al., 2011), especially in a complex geological setting, exemplified by an ophiolitic area. Ophiolite is an oceanic crust and upper mantle fragments that have been tectonically uplifted and emplaced onto the continental crust (Brooks, 1987). It typically includes ultramafic and mafic rocks (largely peridotites, dunites, and gabbros) with varying degrees of serpentinization (Barnes et al., 1978). These rocks are composed of ferromagnesian minerals (e.g. olivine, pyroxene, and serpentine) with an elevated level of heavy metals, such as Cr, Ni, Zn, Co, V and Sr (Al-Riyami et al., 2002). Ophiolites present important groundwater resources in some areas (e.g., in Grecee (Voutsis et al., 2015) and in Italy (Segadelli et al., 2017)). However, ophiolites may impact strongly the chemical composition of the water (e.g., in Oman (Paukert Vankeuren et al., 2019)) because of the high reactivity of the rock-forming minerals, which makes some water sources unsuitable for human use. In a general manner, the chemical weathering of ophiolitic rocks results in the formation of clays and iron oxides minerals and a release of dissolved constituents such as heavy metals to soil and waters (Tashakor et al., 2018; Critelli et al., 2015). Previous studies showed that the Cr and Ni contents in some springs in ophiolitic areas exceed the maximum permissible limit for total Cr and Ni of drinking water (WHO, 2011) in Italy, Grecee and Turkey (Fantoni et al., 2002; Voutsis et al., 2015; Hatipoglu-Bagci & Bayari 2020). Although ophiolite may host one of the groundwater resources in Syria, few studies on its groundwater quality have been carried out (Adra et al., 2020), contrasting to other aquifers (e.g. karstic and alluvial) (Kassem, 2001; Asmael et al., 2021). Because of the climate change, the urbanization with insufficient infrastructure, and an inadequate water resources management (Asmael et al., 2021) in recent, the problem of water scarcity in Syria has been exacerbating. Thus, the exploration of new water resources and the assessment of its quality and quantity are necessary in Syria. Since the Bassit is a large drainage area in Syria, which consists of extensive outcrops of ophiolitic rocks, it was selected as the study area. The aim of this work is to 1) investigate the hydrogeochemical characterization and to assess the quality of groundwater in Bassit area and 2) to determine the concentration of certain heavy metals (Cr, Ni, and Co) in the groundwater.

The Bassit region (Figure 1) lies in the northwestern Syria along the Latakia coast

for approximate 40 km and rises gradually to an average height of 1000 m above sea level, the forest covers more than 70% of the region. The Bassit is separated from the Coastal Mountains in south by the El-Kabir river valley. The study area is characterized by Mediterranean climate type with a long dry summer and rainy winter. The annual average of rainfall ranges from 700 to 1000 mm/year. The villages are located in the western and southern parts of the study area and the majority of people depend on the agriculture in their livelihood and use groundwater for their domestic and irrigation purposes. No industrial activities exist in the region.

The Bassit ophiolite association is a part of the periarabic Arc (Figure 1), which consists of ophiolite allochthones thrusted over the sedimentary cover of the African-Arabic platform and extending from Oman through the central Zagros (Iran) and the foothills of the Eastern Taurus (Turkey) to northwestern Syria and Cyprus (Knipper et al., 1986). The Bassit ophiolite complex makes up the Baer-Bassit nappe, which represents the upper structural stage of the allochthone section. The Tamima nappe represents the lower nappe of the section which is composed of Upper Triassic–Lower Cenomanian volcanic and sedimentary rocks (Parrot, 1980; Knipper et al., 1986). The obduction of the ophiolite complex in late Maastrichtian resulted in the emerging of these rocks and their lateritic weathering. At the end of the Cretaceous period, the folded-nappe allochthon structures again submerged beneath sea level and were covered by Upper Maastrichtian-Pliocene carbonate sediments 300 - 1200 m thick. According to Knipper et al. (1986), The Bassit ophiolte nappe consists from bottom to top of 1) Gabbro–hyperbasite complex which ranges up to 1.5 km in thickness and composed of serpentinized dunites and harzburgitic tectonites; 2) diabase-gabbro complex which is widespread in the region and consists of norites, gabbros, diabases and diorites; 3) Two pillow-lava horizons (tholeiite basalts and boninitic rocks). Hydrogeologically, very few studies were done about the hydrogeological properties in Bassit area. Generally, the region is lack of available water resources, the ophiolitic rocks may represent the main aquifer in the study area, which is exploited through few bore and dug wells with depths ranging from 40 to 75 m. The ophiolitic complex aquifer is impermeable and highly fractured by faults (Poisson, 1977; Critelli et al., 2015). Recharge to the aquifers takes place through the snowmelt, rainfall events, and lateral and downward groundwater flow from overlying strata (like karstic). Springs are the main way of groundwater discharge, which are mainly associated with the ophiolitic complex. However, the flow of springs depends on the annual precipitation, which increases in wet season and may ceases in dry season.

To analyze the physico-chemical properties of groundwater in the study area, a total of (27) groundwater samples were collected from (6) springs and (8) hand-dug wells with a buried depth between (40 - 75 m) during the wet season (April 2020) and the process was repeated during the dry season (August 2020). The sampling sites are illustrated in (Figure 1). Standard methods (APHA, 1998) were adopted in the collection, preservation, and analyses of samples. The parameters, i.e. temperature, electrical conductivity (EC), pH, and total dissolved solid (TDS), were measured using a multiparameter WP600 series in the field immediately after pumping out for 10 - 20 minutes. The groundwater samples were taken and stored in the acid-washed polyethylene bottles. The collected samples were kept in the refrigerator at 4˚C for test. The determinations of Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SO 4 2 − , and NO 3 − were performed by an ion chromatography (Shimadzu-IC). The content of HCO₃⁻² was measured using an acid–base titration. Total hardness (TH) was calculated as TH = 2.49 Ca²⁺ + 4.11 Mg²⁺ (Todd, 1980). Determination of some heavy metals (Cr, Ni, and Co) was performed by a graphite furnace atomic absorption spectroscopy (Shimadzu AA-6800) using certified Cr, Ni, and Co standard solutions. The suitability of groundwater for drinking purposes was evaluated by comparing different parameters with those reported by the World Health Organization (WHO, 2011), and for irrigation purposes were evaluated by the following parameters: 1) Soluble sodium percentage (SSP or Na%) is an indication of sodium hazard in soil. A high Na% in soil can have dangerous impacts on soil aeration, structure and infiltration. It was calculated by the following equation (Equation (1)) (Todd, 1980):

% Na = [(Na⁺ +K⁺) × 100]/(Ca²⁺ + Mg²⁺ + Na⁺ + K⁺) (1)

2) Sodium adsorption ratio (SAR) is used to express alkali hazard, when the concentration of sodium is high in irrigation water, Na⁺ ions tend to be absorbed by clay particles in the soil, displacing Ca²⁺ and Mg²⁺ ions, which reduce the soil permeability (Selvakumar et al., 2014). SAR is calculated by the following equation (Equation (2)) (Richards, 1954):

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

3) Magnesium adsorption ratio (MAR) also recognized as magnesium hazard (MH) and is calculated as per method suggested by Ragunath (1987) as (Equation (3)):

MAR = Mg 2 + × 100 Ca 2 + + Mg 2 + (3)

The present work reveals adequate background information on hydrogeochemical properties and contamination levels of some heavy metals in the groundwater in the Bassit ophiolitic area (northwestern Syria). The results demonstrate that the groundwater is very hard and slightly alkaline in nature. The concentrations of major ions are in the following order: Mg²⁺ > Ca²⁺ > Na⁺ > K⁺ and HCO 3 2 − > Cl⁻ > SO 4 2 − > NO 3 − . The dominant hydrogeochemical facies of groundwater in the study area are Mg-HCO₃ (up to 60% of the samples), Mg/Ca-HCO₃ Mixing type (~30% of the samples) and Ca-HCO₃ type (~10% of the samples), which reflect an influence of ophiolitic rocks on the local groundwater chemistry. No change in groundwater type was recorded temporally (in dry and wet seasons). The maximum concentrations of some heavy metals for two seasons were (Cr_tot 16.9, Ni 19.27, Co 1.78 all in μg/L), which are less than the permissible limits for drinking purpose. Generally, the sampled groundwater was found to meet drinking water quality guidelines for most of the physicochemical quality properties. However TDS, TH and Mg²⁺ concentrations in most groundwater samples were in excess of maximum permissible limits, that could lead to health problems. Groundwater quality for irrigation was classified based on SAR, SSP% and MAR indices, SAR has indicated that all the samples belong to the excellent category. The Wilcox diagram shows that 95% of the samples fall in the field of good to permissible and the remaining samples fall in the field of excellent to good range. The analytical data plotted on the US salinity diagram illustrates that 89% of the groundwater samples fall in the field of C3-S1, indicating high salinity and low sodium water and the remaining samples fall in the field of C2-S1, indicating medium salinity and low sodium water. The magnesium hazard (MAR) shows that 82% of the samples had MAR values high (>50%) and as such unsuitable for irrigation, and the remaining samples classified as such suitable for irrigation as shown in (Table SI-4). Land irrigated with such groundwater will not be exposed to any alkali hazard, but will suffer from a salinity hazard and magnesium hazard. Thus, most of the groundwater in the study area can be used for soils with good drainage conditions which control salinity.

I wouldlike to thank Dr. Hajar Nasser and Dr. Omar Jaafar in the Faculty of science at Tishreen University for their support during the field exercise and for their suggestions that improved the scientific soundness of this manuscript.

The author declares no conflicts of interest regarding the publication of this paper.

Adra, A. (2022). Hydrogeochemical Characteristics of Groundwater in the Bassit Ophiolitic Area, Northwestern Syria. Journal of Geoscience and Environment Protection, 10, 373-392. https://doi.org/10.4236/gep.2022.1012021

Table SI-1. Concentrations of selected elements and physico-chemical parameters of groundwater samples in dry season.

Table SI-2. Concentrations of selected elements and physico-chemical parameters of groundwater samples in wet season.

Table SI-3. Concentrations of heavymetals (Cr, Co, Ni) for the groundwater samples in dry and wet seasons.

Table SI-4. Result of irrigation-water parameters for groundwater samples in dry and wet seasons.