Assessment of the Distribution and Source of Arsenic in Karstic Aquifers, Case Study Garu Saline Karstic Spring in East of Khusetan, Southwestern Iran

There are many springs in Iran that are contaminated by arsenic and therefore are not suitable for drinking purposes. Garu spring around Masjed Soleyman city is an indicator of such springs. In order to study the concentration of arsenic, 20 samples from spring and Asmari anticline observation wells were collected. Concentration of major and trace elements in the samples were measured. ICP-OES studies were carried out on 3 samples of the surrounding formation. The results showed that Garu spring has arsenic levels higher than 10ppb. Hydrochemical and statistical analyzes of water samples and sediment as well as significant correlation of arsenic with main cations, (i.e. Nickel and Vanadium) shows that anthropogenic factors do not have an effect on the amount of arsenic. It is found, that the origin of arsenic is geogenic (Gachsaran formation and oil brine influx). The mechanism of arsenic mobility during the wet season is the anaerobic respiration of Fe+3 reducing bacteria. Whereas, in the dry season, the environment is further reduced, as a result activity of the SRB and IRB in the span of springs leads to the reduction of iron by sulfide from sulfate respiration, this causes arsenic deposition. Also, gas chromatography analysis of the oil presented in spring shows that H2S is the result of thermochemical reduction of sulfate in carbonate reservoirs. According to the results of this study, the use of water resources in the region threatens the health of the inhabitants of the region, and arsenic removal methods should be used.