Assessing Groundwater Vulnerability in Lenjan district toTotal Organic Carbon, Nitrate and Cations and Anions using GIS in Pilot Scale

Groundwaters can be polluted due to various natural and anthropogenic activities. These water resources are directly used as community’s drinking water. Therefor, pollution vulnerability assessment of them can help the local and national managers and decision makers in control of many discharged pollutants. For this purpose, the aquifer vulnerability of Najaf Abad plain (Lenjan District) has been surveyed in this study.
Today, Geographical Information System (GIS) is used for assessment of vulnerability of groundwater systems. Therefor, GIS was also used to determine the different degrees of vulnerability in the study area. For this purpose, different information layers were prepared. These information layers included electrical conductivity, nitrate, total organic carbon, sulfate, chloride and total hardness concentration which were obtained from 25 wells in Lenjan district through sampling during 4 seasons from summer of 2008 to spring of 2009.
Finally, after weight ratings and overlaying of the information layers, the vulnerability of areas were determined both seasonally and annually.
Results of chemical analysis of the samples showed that the highest concentrations of nitrate, total hardness, chloride, sulfate and EC levels for spring of 2009 were 98, 3800, 6745, and 3780 mg/L and 14.5 mS/cm, respectively. In contrast, the highest concentration of TOC occurred in summer of 2008 was 21.6 mg/L. However, the lowest concentrations of these agrichemicals were recorded in summer and autumn of 2008.
The results obtained with the help of GIS showed that the area in the center of Lenjan district, that had clay type of soil and average groundwater depth compared to the adjacent regions, had the lowest vulnerability to analyzed pollutants. Therefore, vulnerability of the areas increased by moving towards the east of Lenjan district. Thus, digging a well in this vulnerable area will be faced with water resources pollution