Investigating the Groundwater Quality of Zanjan Plain Based on Drinking Standard with Geostatistics Methods

Groundwater resources management is very important in arid and semi-arid areas. Water for drinking and agriculture is very limited in terms of quantity and quality. Increase of population and urbanization, technology development and uncontrolled discharge of domestic, industrial and agricultural sewage in water bodies due to that use of this water resource is limited while the demand for them is greater always. Increased utilization of these valuable resources has led, not only reduce the quantity of groundwater resources, but also the quality of these resources is declining Thus use of methods that can able to determine the condition of these resources for management is required. Study of spatial variation of groundwater quality parameters have important role in recognition of aquifer quality condition, pollution sources and determination the most suitable managerial strategies. To achieve this aim, monitor and evaluate the quality of groundwater resource is expensive and hard work, therefore accessible and inexpensive methods such as Geostatistics and GIS are useful in this regard. The aim of this research is to evaluate the parameters distribution such as EC, TDS, TH and pH in the groundwater of Zanjan Plain by using of Geostatistics method as IDW, RBF, GPI, LPI and OK in ArcGIS software and spatial distribution maps of these parameters was prepared. Finally, the water quality is determined by using of Drinking World Standard in the Zanjan Plain.2- MethodologyIn this research, pollutants distribution of EC, TDS, TH and PH in Zanjan plain which is located in zanjan province, assessment by using of different methods of geostatistical such as Inverse Distance Weighting (IDW) method and Radial Basis Function (RBF), Global Polynomial Interpolation (GPI), Local Polynomial Interpolation (LPI) and Ordinary Kriging in ArcGIS software, and spatial distribution maps were prepared for each one. Accordingly, groundwater samples of 34 wells were analyzed. After the variogram reviewed and the spatial variations of parameters studied, parameters with mentioned different ways interpolation was done and using with Cross Validation method and Root mean square error the best model for evaluation with the lowest RMSE was selected.3– DiscussionIn classical statistical analysis, samples were obtained from the community are randomly assigned and Measured value of a certain quantity in a particular sample, do not have any information about the same value of the quantity in the another sample and with clear distance. While Geostatistic methods can be used to make a relation between values of quantity in population, samples, the distance and orientation of the samples to each other. To evaluation the accuracy of methods can use of the Root Mean Square Error (RMSE). The best method has the lowest RMSE. Results showed that the TDS and TH parameters had lowest RMSE with using RBF method, PH and EC parameter had lowest RMSE with using IDW method and to catering spatial distribution map of groundwater quality parameters used with methods. Assess the trend of spatial distribution for EC, TDS and TH in the Zanjan plain show that concentration of them increases as linear in the west to east and from north to south. Spatial distribution trend of pH show that variability has the U Curve form and increase in the west to east and from north to south of zanjan plain.4– ConclusionAccording to the drinking water standards of the world health organization and map obtained with using from geostatistical method, the results showed that pH parameters in the plains don’t have limits for drinking. EC parameter in the Four wellsValaiesh, Dizaj Abad, Zanjan and Mehtar that are located in southeastern, center and northwestern of plain, have limited due to agriculture actions. TDS parameter have limited in the total of the zanjan plain except the northeastern in terms of drinking. In the many wells, TH parameter has limitation effect. In the terms of water hardness, total wells of zanjan plain are located in the hard and the hardest class. The excessive harvesting of groundwater resource and illegal drilling wells and industrial actions development can be the reasons for decreasing trend of groundwater resources quality