Evaluation of mapping methods in spatial distribution of groundwater quality indicators (Case study: Turkmenchay region)

Spatial variations in the qualitative indicators of groundwater resources are among the factors influencing the policies of harvest management and consumption of these resources. In arid and semi-arid climatic zones, groundwater is one of the important resources for exploitation for various purposes, especially agriculture and drinking and importance study of its quality indicators in order to assess the possibility of using water resources. In this research, the accuracy of kriging and cokriging statistical methods as well as definite inverse weighted distance methods and radial base functions to predict the spatial distribution of groundwater quality parameters including chlorine, sodium, magnesium, calcium Sulfate, sodium adsorption ratio, total solute concentration and electrical conductivity were investigated in Turkmenchay region. In order to evaluate the results, cross-evaluation method and MAD, RMSE and R indices were used. Based on the obtained results, the cokriging method is the best method for zoning all the studied indicators. RMSE values for electrical conductivity are 130.67 μmohs/cm, total solute concentration is 61.13 mg/lit, calcium concentration is 0.84 meq/lit, magnesium concentration is 0.53 mg/lit, sodium concentration equal to 0.63 meq/lit, chlorine concentration equal to 0.41 meq/lit, sulfate concentration equal to 0.58 meq/lit and Sodium absorption ratio was obtained as 0.31 meq/lit were reported. Also, the evaluation of the results obtained from the spatial distribution of indicators showed that the groundwater resources in the whole study area are in a favorable condition for use for various purposes, which is more evident in the northern half of the study area. Due to the trend of changes in the concentration of elements in the area of Khajeh Ghias village, in order to improve the conditions and provide policies for extraction and consumption of groundwater in order to prevent a decline in water quality, it is recommended to monitor water quality regularly.