Investigating of Samalqan aquifer groundwater quality base on underground variations of alluvial and rock facies

Generally, the groundwater chemistry depends on many factors, including the quality of the recharged water, the hydrogeological‏ conditions, water-rock interactions‏, human activities etc‏ (Kumar et al., 2012). According to these processes, the chemical composition of groundwater varies with respect to space and time and the concentrations of chemical species increase in groundwater flow path (Sharif et al., 2007; Suma et al., 2014;  Rattan et al., 2005)‏. The water-rock interaction and the types of chemical reactions (dissolution, precipitation, ion exchange processes, redox etc.), which effected on groundwater quality, usually is determined in the discharge point. Based on chemical composition, the quality of groundwater‏ is classified to drinking, industrial, and agricultural categories (Elgano and Kannan, 2007, Subramani et al., 2005). Assessing the quality of groundwater and surface water resources, especially in areas related to groundwater for drinking, is very important. Rocky and alluvial facies have different effects on the quality of water resources (Clark, 2015). Sedimentary rocks and minerals, especially minerals in evaporite formations‏ damage the water quality (Jagadeshan et al., 201; Ozman et al., 2011; Redwan et al., 2016; Choi et al., 2013). The most important aim of this paper is to investigate the subsurface alluvial deposits and geological formations (rocky and alluvial facies) and their effect on the chemical characteristics of water and the water quality for various uses (drinking, agriculture, and industry) in Samalqan plain. The collected drilling‏ data of 15 exploitation wells from North Khorasan Regional Water Company, has been used for the purposes of this study. Sampling from deep wells in different parts of the plains has been done to assess the water quality in both wet and dry seasons in Year 1392-93. Arc GIS (10.1), PHREEQC 2.6, Aq.QA, Excel, and RockWorks14 software's were used to generate required maps and diagrams. Using the available‏ drilling logs information in both AA' and BB' directions, the geological layers of sediments were investigated in the Samalqan plain. Based on dfistribution of coarse sediments in the North East of the plain (in AA' cross section), the water table depth increases from the northeast to the southwest. As drilling logs show, the geological facies changes in this direction and it shift from gravel in the southwest to muddy and sandy in central part of the plain and finally to gravelly in the northeastern parts of the plain. In BB' trend, along the east - west and north of the plain, the Tirgan Formation facies and the Neogene sediments have an important role in the quality of water resources. The drilling logs in this direction indicate that the gravelly sandy and muddy facies is visible and it changes from muddy to sandy and gravely from East to West. Due to the proximity to facies changing to the limestone of Tirgan Formation, the electrical conductivity (EC) of water shows minimum values in the southern part of the plain. The abundance of cations and anions facies are like Na+ >Mg2+ > Ca2+>K+‏ ‏ and Cl- > HCO3- >SO42-, respectively. According to the Pie chart in both dry and wet seasons, the concentration of bicarbonate is reduced however, the concentrations of sodium, chloride, and sulfate are increase from south to the north of the plain, which is due to the existence of Neogene sediments in the eastern part of the plain and to the lack of aquifer recharge from northern part of the plain. The groundwater equipotential map show that the direction of groundwater flow is toward northern (the output of the catchment) and the type of‏ groundwater changes from bicarbonate to chlorine in this direction. Saturation indexes of minerals indicate more dissolution of halite and gypsum with respect to‏ calcite and dolomite in Samalqan plain. Samalqan water resources have good to unpleasant quality for drinking, and its water is appropriate to un- appropriate in terms of agricultural usages and it is corrosive sedimentational in industry point of view. We need to appreciate the efforts of Dr. Mohammad Vahidinia, Dr. Asadullah Mahbuobi and Dr. Mohammad Khanehbad, from Ferdowsi University of Mashhad, Mr. Davarpanah, head of Ashkhane water affairs, Mr Karimi, head of Ashkhaneh water affairs archives, Mrs. Bakhshabadi, secretary of water resources studies of North Khorasan Regional Water, Mr. Bahrami and Mr. Moniri, East Abkav company, Mr. Abyari, digger of Yazd Abgune company. As well as we thanks the efforts of Mr. Moheghi, Mr. Sohrabi, Mr. Asemani,Mr. Eskandari, Mr. Shadmehr, Mrs Zandvakili and Mrs Valizadeh.