Groundwater quality Zoning Based on Wilcox Index Using Geographic Information System in Jajarm district, north Khorasan, Iran.

The qualitative data of underground water of Jajarm city, Iran, was analyzed using geographic information system (GIS). The interpolation technique was used for the assessment of selected factors, including electrical conductivity (EC), total dissolved solid (TDS), total hardness (TH), sodium adsorption ratio (SAR), and Cl. These parameters of almost all wells in Jajarm region were applied for the spatial analysis. These parameters were measured for 14 wells in central region of Jajarm for zoning water quality class based on Wilcox index. Accordingly, four wells (Jajarm, Ghaleh Gazi, Daragh, and Kaftarac), involving 28.57% of wells, were within average order class of water quality for agricultural purposes. Their water quality was in class S1 status. Other 10 wells were in the bad order class, meaning inappropriateness of about 71.43% of the wells in Jajarm plain for agricultural purposes. Khoshab and Shah Abad wells had the worst status. By classifying the suitability of water quality for agricultural purposes based on EC, the water of these stations were classified as class C4, and based on SAR as class S4. The results indicated that the greatest decrease in water quality was in the southwestern parts of the study area, and decline in some parts of the desert, such as the southern region of Jajarm plain, was highly tangible and obvious. The decrease in water quality could be attributed to climate change, excessive use of water, and the changes and decline in rainfall.