Comparison of the SINTACS Aquifer Vulnerability Model to Nitrate with Three-Dimensional Numerical Model (Case Study of Varamin Plain Aquifer)

Groundwater in arid regions such as Iran plays a very large role in drinking water supply and agriculture. One of the threats to the future of groundwater exploitation, could be the contamination of these resources by harmful substances. At present, about 60% of the water consumption of Varamin plain region and the total volume of water consumption in the drinking sector is provided from groundwater sources. One of the best ways to prevent groundwater pollution is to identify vulnerable aquifer areas. The SINTACS model has been used to assess the vulnerability of the Varamin plain aquifer. This method consists of seven parameters that after combining the parameters, the vulnerability index map is obtained. The index of this method varies between 92 and 168.Results show that the north of the plain is very vulnerable and vulnerability is low in the south-eastern parts of Jalilabad village and downstream areas of the plain, while the rest of the plain has moderate vulnerability. A three-dimensional numerical model was used to evaluate the results of the model and the model was validated for a period of one year. The accuracy of the constructed model was evaluated as appropriate. In this model, nitrate contaminant was considered as an aquifer contaminant. In order to validate the inherent and special vulnerability of the SINTACS model, the nitrate output of the model was used, The correlation square of the results was about 65%, which shows a good agreement between the two models even thogh the numerical model is considered as micro- model compared to SINTACS one. Considering the role of the aquifer of Varamin plain in supplying the required water of the region, the quantitative and qualitative protection of this aquifer is a necessary and strongly recommonded. Also, in order to reduce the nitrate ion concentration in the study area, long-term solutions such as improving the agricultural structure and cultivation pattern of the area and constructing a collection network and wastewater treatment plant are proposed.