Environmental Hydrogeochemistry Characteristics, Controlling Factors and Groundwater Quality Assessment in Herat City, West Afghanistan

Abstract

Water in Central Asia is a precious resource in the semiarid and arid environments in which people live in the region. Understanding the groundwater quality is important as it is the main factor determining its suitability for drinking and agricultural purposes. This paper presents results of a groundwater hydrochemical assessment in the Herat City by measuring its physicochemical parameters: major cations and anions, pH, total dissolved solids and electrical conductivity. In the light of progressive depletion of groundwater reservoirs and water quality deterioration, an investigation of dissolved major constituents in 27 groundwater samples was performed. The objective was detection of processes for geochemical assessment throughout the area. Herat City has been intensively inhabited during the last decenniums, leading to expansion of the residential and agricultural areas. Besides semi-aridity, rapid social and economic development stimulates greater demand for water, which is gradually fulfilled by groundwater extraction. Groundwater of the study area are characterized by the dominance of Ca + Mg over Na + K. $${\text{HCO}}_{{\text{3}}}^{ - }$$, which was found to be the dominant anion, followed by Cl– and $${\text{SO}}_{4}^{{2 - }}$$. The hydrochemical types in the area can be divided into two major groups: the first group includes mixed Ca–Mg–Cl and Ca–Cl types. The second group comprises mixed Ca–Na–HCO3 and Ca–HCO3 types. Calcite and aragonite have high SI values, which indicates precipitation as the result of evaporation, whereas dolomite shows an undersaturation state. Most of the samples are within the permissible limit of WHO standards. Interpretation of data suggests that weathering, ion exchange reactions, and evaporation to some extent are the dominant factors that determine the groundwater chemistry in the study area.