Investigation of hydrochemical characteristics of groundwater in the Harzandat aquifer, Northwest of Iran.

The Harzandat plain is part of the East Azerbaijan province, which lies between Marand and Jolfa cities, northwestern of Iran, and its groundwater resources are developed for water supply and irrigation purposes. The main lithologic units consist chiefly of limestone, dolomite, shale, conglomerate, marl, and igneous rocks. In order to evaluate the quality of groundwater in study area, 36 samples were collected and analyzed for various ions. Chemical indexes like sodium adsorption ratio, percentage of sodium, residual sodium carbonate, and permeability index were calculated. Based on the analytical results, groundwater in the area is generally very hard, brackish, high to very high saline and alkaline in nature. The abundance of the major ions is as follows: Cl(-) >HCO3(-)>SO4(2-) and Na(+) >Ca(2+) >Mg(2+) >K(+). The dominant hydrochemical facieses of groundwater is Na(-)Cl type, and alkalis (Na(+), K(+)) and strong acids (Cl(-), SO4(2-) are slightly dominating over alkali earths (Ca(2+), Mg(2+)) and weak acids (HCO3(-), CO3(2-). The chemical quality of groundwater is related to the dissolution of minerals, ion exchange, and the residence time of the groundwater in contact with rock materials. The results of calculation saturation index by computer program PHREEQC shows that nearly all of the water samples were supersaturated with respect to carbonate minerals (calcite, dolomite and aragonite) and undersaturated with respect to sulfate minerals (gypsum and anhydrite). Assessment of water samples from various methods indicated that groundwater in study area is chemically unsuitable for drinking and agricultural uses.