Abstract
Wellhead protection area is delineated around a water supply well and represents the area contributes recharge to the pumping well during a specific period of time. This area must be protected to prevent the groundwater contamination. Groundwater modeling using computer is found to be the most appropriate method for this task. In this study, groundwater modeling was used for the delineation of wellhead protection area. WhAEM2000 (v.2.1.0) model based on analytic element method has been used for this purpose and 2-year time of travel WHPAs were mapped for pumping wells drilled in the basin of Shahr-Chai River, located in Urmia plain. Steady state flow was applied in unconfined model which included the main surface water features (rivers and lake), recharge rate due to precipitation, irrigation and periodical tributaries, and inhomogeneity to represent the western area of the plain with different characteristics. This model was subsequently calibrated by means of test points representing the observing heads to which the modeled heads had to be equal. In confined aquifer of Urmia plain, the groundwater does not have interaction with surface waters and no recharge penetrates into the aquifer. For this reason, uniform flow was applied to create a new model for which the direction of the flow and the hydraulic gradient should be specified. These two parameters were evaluated using the approach called three points method in which three observing wells are utilized to calculate the regional hydraulic gradient and the orientation of groundwater flow. No calibration was implemented due to the lack of data related to the piezometric heads and the only solution was the hypothesis testing. The results indicate that the wellhead protection areas of the wells in the unconfined aquifer of the plain are much longer and narrower than those in the confined aquifer and the delineated areas include most of the residential lands of Urmia city. In addition to the above works, the effects of adjacent pumping wells, interaction between the pumping wells and the recharge wells (representing wastewater wells), the effects of no-flow boundary were also studied. In the end, the results of WhAEM2000 were compared with the results of other methods including WHPA computer code, which had been employed previously to study the wellhead protection area for the wells drilled in the area of interest. The results of this comparison showed that WhAEM model gives more accurate and reasonable results.