Transport of total dissolved solids into urban discharge sources by irrigation water reuse effect

Alternative sustainable water sources must be identified when water demand is increased. Artificial groundwater recharge for water reuse are supply augmentation methods in water limited areas. Monitoring the present solute transport process is necessary in determining possible threats to drinking water supplies in the future. In this study the groundwater flow is investigated to represent movement and quality transformations for a modeling period of 5 years (Sep. 2002 to Oct. 2007). Total dissolved solids, TDS, concentration as aquifer water quality index was simulated using Modflow and MT3D models in two direct and indirect recharge scenarios. The model has been calibrated under steady state and transient conditions. Hydraulic conductivity and specific yield in flow model and transverse and longitudinal dispersivity and molecular diffusion coefficient in solute transport simulation was calibrated by first four years and was verified with observed data in last year. Seven urban wells were selected as the observation points and the calibrated model was used to evaluate the vulnerability of aquifer on wastewater recharge. The results show that the developed numerical model is capable of simulating the TDS concentration in porous media. Direct and indirect recharge methods increase the average of water table about 4 m and 2 m, respectively. The effect of contaminant transport with concentration of 2000 mg/L is approximately in distance of 200 m. Also, deep percolation of agricultural lands had more effect than advection, dispersion and diffusion terms to groundwater contamination.