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

Groundwater quality data for Jajarm district was studied by using the Geographic Information System. The interpolation technique were used for the selected factors: Electric conductivity, Total dissolved substance , Total hardness, SAR, and Cl. These parameters of nearly all the wells in Jajarm district were used for the spatial analysis. In addition these parameters were measured for 14 wells in Jajarm’s central area for the zoning of water quality class based on the Wilcox index. According to this index, four wells (Jajarm, Ghaleh Gazi, Daragh, and Kaftarac) are in the area of average order class of water quality for agricultural use, including 28.57% of wells. Their water quality status is in class S1. The other 10 wells, are in the bad order class, which means that about 71.43% of the wells in Jajarm plain are not suitable for agricultural use. Among these wells, Khoshab and Shah Abad have the worst conditions. By classifying the suitability of water quality for agricultural use based on EC, the water from these stations are classified as class C4, while based on SAR, they are classified as class S4. The results exhibited that the highest decline in water quality was in the south-western parts of the study region, and decline in some parts of the desert such as in the southern region of Jajarm plain was very tangible and specified. The decline in water quality can be attributed to climate change, excess use of water, and the variation and decline in water precipitation.