Abstract—Groundwater is one of earth’s most vital renewable and widely distributed resources as well as an important source of water supply worldwide. The increased exploitation of groundwater resources can decrease regional water quality as a whole. The estimation of sodium adsorption ratio (SAR) and chloride content, and also, Na + , Ca 2+ and Mg 2+ concentration are much more time- consuming and expensive than water salinity measurement. Therefore, it is necessary to find a sterategy to estimate SAR and chloride using salinity extent. In this research, kriging and cokriging methods to estimate the parameters including the sodium adsorption ratio (SAR) and the chloride content (Cl - ) based on groundwater salinity data (EC) in Fasa area were applied. Results obtained from two methods were compared together. Results indicated that cokriging has higher accuracy than kriging method in the estimation of the sodium adsorption ratio (SAR) and the chloride content of groundwater in areas with data restriction. Generally, results of this research showed that the two methods differ slightly and they have suitable accuracy to estimate SAR and Cl - based on water salinity parameter. Keywords—Groundwater, sodium adsorption ratio, chloride, geostatistic methods. I. INTRODUCTION ROUNDWATER is one of earth’s most vital renewable and widely distributed resources as well as an important source of water supply worldwide. The usage of groundwater has gradually increased due to of the increase of water demand and the shortage of surface water during the growth of population (NIUA, 2005; Mahmood and Kundu, 2005). Also, this has resulted in the excavation of many wells in most regions in Iran. Thus, excessive use of groundwater aquifers is growing and decrease regional water quality as a whole pointed out that drought and groundwater level drop are the main causes of soil salinity and alkalinity. 1 M. Sc Student in Water Resources Department, University of Zabol, Zabol, Iran. (corresponding author to provide phone: +989153636615; e-mail: mohammad.samin66@gmail.com). 2 Professor in Water Resources Department, University of Zabol, Zabol, Iran. (corresponding author to provide phone: +989151109471; e-mail: Gsoltani45@gmail.com). Salt and Sodium in solids are processes that are affected performance of plants in ariad and semiariad regions. Therefore, in order to the better management of water resources and soil and correct planning to obtain maximum yield in crop plants, determination of essential elements such as sodium and choloride in water is necessary. Iran is located in an arid to semi-arid region of the world and about 95% of fresh water is allocated for agriculture, out of which 80% is supplied through groundwater. So, it is clearly concluded that groundwater is the vital component for sustainable agriculture(Seyed Hamid Ahmadi & Abbas Sedghamiz,2007). Since estimate the amount of chloride and determination sodium absorption ratio (SAR) and the concentration of Na, K and Mg very time consuming and expensive than measurment of water salinity, find a strategy that could be on the salinity, it seems essential spatial estimation of the amount of SAR and chloride of water. Basically water table levels, salinity and water depth in the region has large variation in different time periods. SAR is a measure of the suitability of water for use in agricultural irrigation, as determined by the concentrations of solids dissolved in the water. The formula for calculating sodium adsorption ratio is (Suarez et al.,2006): (1) Where, sodium, calcium, and magnesium are in mq/l. Safari used kriging method to estimate spatial prediction of groundwater in Chamchamal plain in west of Iran. Results showed that suitable method of geostatistics to estimate one variable depends on variables type and regional factors which influence this and any selected method for given region can not be generalized to others (Ahmed, S., 2002). Rizzo and Mouser used geostatistics for analyzing Groundwater quality. They used microbial data as auxiliary variable in cokriging method. These researchers' results showed that cokriging method has suitable accuracy to estimate Groundwater quality (Rizzo, D.M. and J.M. Mouser, 2000). Ahmad used kriging method to estimate TDS in groundwater and demonstrated accuracy of this method to Spatial Estimation of Groundwater Quality Parameters Based on Water Salinity Data using Kriging and Cokriging Methods P 1 PMohammad. Samin, P 2 PJaber. Soltani, P 1 PZahra. Zeraatcar, P 1 PSeyyed Ali. P 1 PMoasheri, and P 1 PNoushin. Sarani G International Conference on Transport, Environment and Civil Engineering (ICTECE'2012) August 25-26, 2012 Kuala Lumpur (Malaysia) 75