Groundwater Chemistry of the Lenjanat District, Esfahan Province

A hydrochemical analysis was made the groundwater and surface water in the Lenjanat district, which lies between Esfahan and Chadegan Dam along the Zayande Rud. The analysis is based on two data sets, both kindly made available by the ministry of energy (Esfahan Regional Water Organization). The first one consists of chemistry data for over 750 samples from wells, qanats and springs in the area. Collected from 1986-1997. The second comprises 328 analysis of Zayandeh Rud River water collected at six station along the river during the period 1991-1998.The evalution of the hydrochemical facies is described through the use of piper and stiff diagrams. While source rock deductions are made by means of the program WATEVAL. (Hounslo, 1995). Spatial distribution of the EC values in the district is determined through application of Kriging methods and examples are given for temporal chages in EC at a few representative locations.It is shown that the groundwater is of a limestone origin. However, because of frequent contacts with gypsum deposits, gypsum dissolution is strongly affecting the groundwater chemistry of most samples.Furthermore the analysis reveals that there is a natural groundwater flow from northward which seeps into the Zayandeh Rud eventually. The irrigation return flow component is added to this. Although both flow components are small, they carry a significanty higher solute load than the Zayandeh Rud in this strerch of the river. Thus causes the change in the chemical composition of the river as it flows through the lenjanat Distric.Finally it would appear that so- called mixing cell methods may be used to quantify natural groundwater seepage and irrigation return flow components, provided information is available with respect to their chemical composition. Groundwater flow and mass transport modelling would be of practical importance in the study of surface water-groundwater interaction along the Zayandeh Rud.