Modeling Perchlorate Contamination In Coastal Aquifer of Israel

The mathematical model of water flow and contaminant transport was developed and applied for simulating the perchlorate migration in soil and groundwater, in the Israeli Coastal Aquifer. The three-dimensional mathematical model of groundwater flow is presented by set of two-dimensional flow equations for the multilayered system, considering the interflow between layers (based on the MODFLOW code). Perchlorate transport simulations were carried out using the MT3DMS model, which solves the 3-D advection-dispersion equation. Perchlorate was considered as a conservative contaminant: neither sorption nor degradation reactions were taken into account. The GMS 5.1 (Groundwater Modeling System) was adjusted and used as a major platform for the simulations. The hydraulic parameters of four major materials (sandstone, sand, loam and clay) composing the sub-aquifers of the coastal alluvial aquifer and the annual groundwater recharge were assessed by a combination of trial-and-error and least square optimization (the PEST code) using observed groundwater levels during 1978-2004. The location of the contaminant source was assigned to the effluents storage ponds, represented by a strip of 200x50m. The concentration of perchlorate in the percolated water was calculated as a function of time, using measured distribution of perchlorate along the vadose zone and transient simulations of one-dimensional water flow and contaminant transport in the unsaturated layered soil profile. Simulations results indicate that the estimated total mass of approximately 280 ton of perchlorate in the unsaturated zone will be washed out into the groundwater reservoir during the coming 25 years. Simulations of perchlorate migration in groundwater were carried out for the period of 2006-2030. The predicted average advection velocity of the plume was 15-20 m/year. The model allows forecast of the plume migration and assessment of water volume and perchlorate mass being extracted for different water management scenarios. It was found that the most efficient removal of the contaminant can be achieved with simultaneous groundwater abstraction at the plume center, integrated with pumping at the periphery of the plume, avoiding further downstream migration of the perchlorate. Furthermore, we identified feasible scenarios of future water abstraction under which the contaminated groundwater plume will be almost completely reclaimed in 25 years, providing a future enforcement of a comprehensive groundwater management and treatment.