Spatial and temporal changes of groundwater quality in Damghan plain using geostatistics

Damghan plain located in Semnan province and due to lack of water resources need to study the status of water resources for better management. Water resources used in this area supplied from springs and wells. the present study aimed to prepare a spatial distribution map of groundwater quality parameters and compare them in different parts of the aquifer surface using geostatistical methods. Measurement parameters in wells, springs and qanat are (TDS, pH, EC, HCO3-, Cl, Ca++, Na+, %Na, SO42-). The results of descriptive statistics in deep well showed that the highest percentage of changes related to Mg and SO42 variables and the lowest percentage of changes were related to pH. The highest percentage of changes in the semi-deep well is related to HCO3 variable and in the spring it is related to Cl. Also, the highest percentage of changes in Qanat is related to chlorine and calcium, while the lowest percentage of changes is related to TDS. The highest percentage of changes in semi-deep well was allocated to bicarbonate anion and the lowest percentage of changes was related to pH. Among the underground water sources, the spring showed better results in terms of regression coefficients and variogram models. The results of the time changes indicated that the measured qualitative parameters had the most changes in autumn and late spring. The general result of this research indicates that the kriging method with spherical semi-variograms is a suitable method for spatial evaluation of groundwater quality variables in Damghan plain.