Evaluating effects of exploitation of groundwater resources in the aquifer quality

Eshtehard plain has been subjected to over exploitation of ground water in recent years and disregarding to the quality of ground water was led to pollution and salinity of aquifer. In this research the spatial distribution of some of the qualitative properties of ground water such as Electrical Conductivity, the concentration of sulfate and chloride and finally the drawdown of water table are studied. For this purpose, initially on the base of existing data in the field of water table during 1376-90 years, the graph of long-term changes in water levels in the aquifer is plotted and the average annual drawdown is calculated 0.69 meter. Also on the base of continuous measurement of groundwater level of the 16 wells in the study area, the map of iso-level groundwater is produced for the year of 1389-90. Then, 14 resources including 9 wells and 5 aqueducts are selected and two sampling is done in the 1389-90. After chemical analysis of samples, the concentrations of cations and anions suchas sulfate and chloride are determined and the maps of EC, SO4 and Cl are drawn. Also annual comograph of aquifer is produced using arithmetic average for 8 years period between 1382-90. Results showed that owing to limited recharges of the study area, unbalanced exploitation is led to drawdown of water table and changing the flow path in the aquifer. On the base of annual hydrograph, the average annual recharge is 29.7 m cubic meter and average annual drawdown of water table is 0.69 meter which shows the over exploitation of aquifer. The maps of EC, SO4 and Cl indicated that brackish waters has been spread from the north of plain to the southern parts of plain so the EC is increased from 4258.1 micromoss in the 1382-83 to the 6733.9 between 1389-90. Given that in the northern part of plain, the concentration of chloride is high, the infiltration of brackish waters with high chloride has had greater increase than sulfate. So the gradual salitinization of groundwater and the spreading of saltwater front into the fresh water front can be seen in this area as one of the consequences of continuous drawdown of water table or over exploitation. Therefore continuation of the current trend does not draw a clear vision for the plain.