Evaluation of Groundwater Quality in Mashhad Aquifer Using the Indicator Kriging Based on Nitrate Pollution

Using normal Kriging in the evaluation of groundwater quality can not specify the areas susceptible to pollution. In this study, to determine the extent of exceeded nitrate pollution (50 mg/L) as well as identifying the areas susceptible to pollution, nitrate data of 287 wells within an area of 320 square kilometers in Mashhad and the statistical range of 2002 to 2011 was analyzed by R software. The process of evaluation and analysis included re-arranging data sheets, detection of outliers, removing the trend, studying the isotropy, determination of the optimum variogram models for each year, and formulating the spatial and temporal Indicator Kriging. The results showed that Matern semivariogram was the best model for explaining the spatial structure data in each year. Also, in the statistical range respectively 7.1, 5.8, 7.2, 8.5, 8.6, 9.4, 10.4, 2.1, and 2.4 percent of the studied area has passed the pollution allowed limit. It seems that more polluted areas have been controlled since 200 by some strategies such as shutting down the polluted wells, preventing new well digging, transferring water from Doosti Dam, using appropriate agricultural wells for drinking section and implementation of wastewater collection network. In addition, respectively 10.4, 11.7, 12.4, 9.4, 14.3, . , 6, 11.6 and 11.5 percentage of total area was prone to pollution during these years. Therefore, these areas need more attention for monitoring and controlling the source of pollution.