Detection of Hydrogeochemical Status and Salinity Trend in Khoy Plain Aquifer by Statistical and hydrochemical Methods

Introduction
Suitability of groundwater for drinking, irrigation and industrial purposes depends upon its quality. Changes in groundwater quality are due to variation in climatic conditions, residence time of water with aquifer materials and inputs from soil during percolation of water. Multivariate statistical methods are one of the common and important methods for hydro geochemistry study. Saturation index (SI) of minerals in order to get an explanation of the chemical evolution of groundwater. Saturation index can be used to predict responses to groundwater subsurface mineralogical reactions, without rock and soil samples collection and petrographic analysis. This research tries to investigation of this method and makes use of it for hydrochemical studding of groundwater resources of Khoy Plain.
Materials and methods
Khoy plain is situated in the north of West Azerbaijan province, northwest on Iran. The study area has a cold and arid climate with the annual mean precipitation about 344 mm. Qhotur and Aland Rivers are mainly surface water resources of the area (figure 1).
In this study it has been tried to use the PHREEQC software for calculate saturation indices of Khoy plain formations mineral. Groundwater samples were collected from 36 groundwater wells that sampling procedures and chemical analysis were carried out as per the standard methods.
Unstable hydrochemical parameters including pH and EC were measured during sampling on site and also with major ions (Calcium, Magnesium, Sodium, Potassium, Chloride, Sulfate, Carbonate and bicarbonate), minor ions (nitrate and fluoride) were analyzed in hydro geological laboratory of Tabriz University. Groundwater samples have two types, Ca-HCO₃ water type and Na-Cl. Generally, groundwater type is Na-Cl in the south and east area and Ca-HCO₃ in west and north (figure 2).
Results and discussion
According to Piper diagram the majority of samples (recharge area) are fresh water with a temporary hardness (figure 3). EC investigation in area shows that electrical conductivity increase from Southwest to Northeast and East which coincided is in the direction of groundwater flow. In the EC values in east and northeast (output of groundwater) are higher than the other parts of the plain, due to the discharge, evaporation of groundwater, evaporative formations and pumping water from the wells.
Totally, three main effective factors were found on study area hydrochemicaly (figure 4). The first and second factors show the effect of geological formations and general groundwater trend on hydrochemistry of the area. The third factor is influence of human activities. Dissolution of evaporative and carbonate minerals have a main role in groundwater hydrochemistry in addition weathering of minerals controls the concentration of major ions such as calcium and magnesium. Calculation of main minerals saturation index in groundwater also show the rock-water interaction and defined the effect of geological formation minerals such as Miocene and Pliocene on increase of water anions and cations (figure 5).
Conclusion
First and second factors show the effect of geological formations and general groundwater trend on hydrochemistry of the area. The third factor is influence of human activities. Calculation of main minerals saturation index in groundwater also show the rock-water interaction and defined the effect of geological formation minerals such as Miocene and Pliocene on increase of water anions and cations.