Evaluation of Quantitative and Qualitative Management Plans in Varamin Plain Aquifer

Groundwater is the most important source of fresh water supply in arid and semi-arid regions around the world, so it is necessary to maintain it through proper management in the use of these resources. Predicting areas of the aquifer that are most likely to be vulnerable is a powerful tool for optimally managing groundwater resources. Using numerical models, it is possible to predict how the aquifer reacts to the harvesting and feeding of the aquifer, with the prevailing trend or different management scenarios. The purpose of this study is to evaluate the effect of current management plans of the aquifer and the catchment area of the Jajroud River on changes in aquifer water levels and changes in nitrate ion concentration in the Varamin Plain, using numerical modeling. In this study, the effect of aquifer and catchment management plans of Jajrud River on changes in aquifer water level and changes in nitrate ion concentration in Varamin Plain, using numerical modeling. In this study, first a quantitative model was prepared in GMS software using MODFLOW code and then qualitative data were entered into the model.  MT3D code was used to run the model. The model was simulated in both stable and unstable modes. After calibrating the model, the hydrodynamic coefficients were corrected and then, using the obtained model, the quantitative and qualitative behavior of the aquifer for the coming years was predicted for two management scenarios. The resulting model showed that with the continuation of the current trend in the aquifer (first scenario), the trend of quantitative and qualitative decline of the aquifer will continue as in previous years, but in the second scenario, with reduced harvesting from wells, municipal wastewater treatment plant will be commissioned. The artificial feeding of the aquifer and the use of the effluent of the Tehran water treatment plant to irrigate the Varamin Plain will significantly reduce the water level decline. Comparison of model implementation in the first and second scenarios shows that with the implementation of planned projects, part of the quantitative problems of the aquifer, especially in the northern areas of the plain will be reduced, so that in some areas, groundwater loss calculated in the quantitative model of the first scenario (until 1420) is reduced by about 30 to 40 meters. The output maps of the qualitative model of the first scenario show that in 1420 the concentration of nitrate in a large part of the aquifer will reach over 40 mg/L, which indicates serious health threats to the region. Simulation in the second scenario shows that the implementation of artificial feeding plan and feeding the aquifer with the effluent of the wastewater treatment plant (with a concentration of 50 mg/L) will not have much effect on reducing nitrate in the aquifer. In general, the implementation of nutrition and consumption management plans in the Varamin aquifer can only lead to a reduction in the quantitative and qualitative decline of groundwater in the aquifer that does not significantly reduce the percentage of water entering the aquifer. Certainly, using the current management methods (second scenario) will not have much effect on improving the aquifer. In addition to the plan to import wastewater from the Tehran treatment plant to the Varamin Plain, the plain should continue to be fed from the Jajrud River as a suitable natural feeding source.