Determination of the travel time and path of pollution in Iranshahr aquifer by particle-tracking model

Recognitions and predictions of the contamination origin are essential steps in the protective measures to avoid well-water contamination and the first step in managing groundwater resources. In this regard, finite-difference model software (GMS 10.0.6) was used to model the transport path, the origin of contaminants and to determine the wellhead protection area in Iranshahr aquifer. Since contamination transport models require a calibrated groundwater flow model, we first prepared this model. Accordingly, after collecting all geological, meteorological, hydrological and hydrogeological data (based on the maps, geophysical tests and exploratory borehole drilling, rainfall statistics and groundwater level in exploitation wells), a database was constructed in ArcGis10.1 software and a conceptual model was developed by transporting this information to GMS software. Based on the developed model, the aquifer's groundwater level was simulated, calibrated and validated using MODFLOW2000 code in GMS software. The particle transport model in the aquifer was provided to examine and model the transport path and the origin of contaminants through MODPATH module. In the end, the aquifer wells' protection area against contaminants was illustrated. According to the results, contaminant transport path in the wells of central plains is directed from the river to the wells, in forward particle-tracking model; the maximum time taken by particles is 508,952.5 days, the minimum time is 144 days, and the average radius of 50-day wellhead protection area based on the protection against contaminations such as pathogenic bacteria in Iranshahr aquifer was determined to be about 100 m.