ناهید مجیدی خلیل آباد

Groundwater quality degradation due to geogenic and anthropogenic factors can endanger the human health. Therefore, designing a groundwater pollution monitoring network can provide the information needed for achieving water resources management goals and improving water and food security. The main objective of this study was to introduce an integrated approach for designing a groundwater pollution monitoring network based on index-based groundwater “protection-monitoring priority” maps created with GIS. The raster layer of “protection-priority index” was prepared by combining aquifer intrinsic vulnerability maps, produced based on the DRASTIC model, and estimated groundwater value based on the quantity and quality of groundwater. Moreover, by overlying pollution-sources risk maps and capture zone maps for wells, qanats and springs, the “monitoring-priority index” was obtained. By overlying the "protection-priority index" and "monitoring-priority index" layers as well as considering the direction of groundwater flow, sampling points were determined. By applying the proposed method, 15 wells were selected for groundwater sampling in Khash-Poshtkuh study area. Water samples collected from these wells revealed that, the concentration of toxic elements such as Arsenic is higher than the permissible limit for drinking in some wells in the southeast and north of Khash aquifer and the north of Poshtkuh aquifer which have geogenic origin.

Determination of wells' capture zones are one of the important issues which must be considered in every aquifers. Methods used for depicting this area divides into two simple and complex methods. Through the simple one several mathematical equations utilized and in the complex method, numerical models are applied. In this study, for the first time, the capture zone of the extraction wells in a standard confined aquifer and Birjand unconfined aquifer was determined using Feflow simulation model. After the simulation procedure in the period of 1390-1391 with monthly time step, the groundwater head is obtained, then the capture zone for each well was depicted. In confined aquifer this area individually determined for 3 extraction wells in two periods of 50 and 180 days. The results showed that the extension of the capture zone for all three wells is toward the part of the aquifer with higher groundwater level. Also, the results revealed that, in areas of the aquifer with higher transmissivity coefficient, the zone is more extended and for the areas with lower transmissivity coefficient, its width decreases and becomes narrower. For instance in second well the width of capture zone in the third zone is 302.86 m, however, it is 267.46 m in the second zone. In Birjand aquifer which consists of 190 extraction wells, 5 wells were chosen randomly to depict capture zone for them in five years and thirty years period. The results revealed that the extension of the capture zones were corresponded to the flow direction. Also, extraction rate of wells and hydraulic conductivity coefficient were two effective parameters in the shape of these zones. As the fifth well in Birjand aquifer with the least value of discharge rate had the smallest length of capture zones among all the wells.