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 geographicinformation system (gis). the interpolation technique was used for the assessment ofselected factors, including electrical conductivity (ec), total dissolved solid (tds), totalhardness (th), sodium adsorption ratio (sar), and cl. these parameters of almost all wellsin jajarm region were applied for the spatial analysis. these parameters were measured for14 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. theirwater quality was in class s1 status. other 10 wells were in the bad order class, meaninginappropriateness 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 waterquality for agricultural purposes based on ec, the water of these stations were classified asclass c4, and based on sar as class s4. the results indicated that the greatest decrease inwater quality was in the southwestern parts of the study area, and decline in some parts ofthe desert, such as the southern region of jajarm plain, was highly tangible and obvious. thedecrease in water quality could be attributed to climate change, excessive use of water, andthe changes and decline in rainfall.