Hydrogeochemical characteristics and groundwater quality assessment for drinking and irrigation purposes in the Mazar-i-Sharif city, North Afghanistan

Abstract

The Mazar-i-Sharif city is part of the Balkh province, north of Afghanistan, and its groundwater resources are developed for water supply and irrigation purposes. The main lithological units consist chiefly of evaporite, conglomerate, sandstone, siltstone, and loess. In order to evaluate the quality of groundwater in the study area, 28 samples were collected and analyzed for various ions. Chemical indices like sodium adsorption ratio, the 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− > SO42− > NO3− and Na+ > Ca2+ > Mg2+ > K+. The dominant hydrochemical facies of groundwater is the Na–Cl type, and alkalis (Na+, K+) and strong acids (Cl−, SO42−) are slightly dominating over alkali earths (Ca2+, Mg2+) and weak acids (HCO3−, CO32−). About 67% of the samples were showing a high concentration of nitrate, exceeding permissible limit of WHO (50 mg/l). The sources of NO3− in the study area are anthropogenic activities (domestic wastewater infiltration from the cesspits) and intense agricultural practices in nearby areas (Balkh district) of the city that utilize nitrogen and sulfate fertilizers. The chemical quality of groundwater is related to the dissolution of minerals, ion exchange, anthropogenic activities, and the residence time of the groundwater in contact with rock materials. The results of calculation saturation index by computer program PHREEQC show that nearly all of the water samples were supersaturated with respect to carbonate minerals (calcite and dolomite) and under-saturated with respect to sulfate minerals (gypsum and anhydrite). Assessment of water samples from various methods indicated that groundwater in the study area is chemically unsuitable for drinking and agricultural uses.