Determining the Areas Prone to Treated Wastewater Replacement through Hierarchical Analytical Method (AHP) in Mashhad Plain

In this study, GIS software was used to locate prone to treated wastewater replacement. For this purpose, parameters of water quality, being close to the wastewater treatment plant, groundwater level, and topographic conditions have been used in different regions. Then, the information layers related to these parameters were weighted through the AHP method. Eventually, by integrating and assembling the layers, a priority map of areas prone to wastewater replacement was drawn. The results of AHP analyzes indicated that according to the water experts, the drop in water level and the quality of groundwater in Mashhad Plain have the highest weighting factor and the distance from the wastewater treatment plant and the height differences in various regions relative to thewastewater treatment plant (topography) were the least weighted coefficient. Also, the areas with the highest drop, the best water quality, the lowest distance and the lower height relative to wastewater treatment plant had the highest weight coefficient. Furthermore, areas with the lowest drop, the worst water quality, the highest distance and height relative to the wastewater treatment plant had the lowest weight coefficient. The areas identified as the first priority indicated the highest water level drop and their water quality was better than other areas of the plain. Therefore, by replacing the agricultural wells of these areas with the treated wastewater and removing these wells from operation circuit, the amount of water withdrawal is reduced and the stored water potential can be used in the future. By direct replacement of the wells with wastewater and excluding these agricultural wells from operation circuit, one hundred percent of replaced water can be stored in the groundwater tables with higher quality and it is possible to use them in the future.