Hydrogeochemistry, circulation path and arsenic distribution in Tahlab aquifer, East of Taftan Volcano, SE Iran

Abstract

The geochemical composition of waters from wells fed by Taftan aquifer located east of Taftan volcano, mainly focusing on the distribution of arsenic, was investigated in order to provide insights into the geochemical processes controlling the chemistry of the shallow aquifer and the possible influence of hydrothermal fluids from the volcano on groundwater quality. For this purpose, 16 water samples were collected and analyzed for the determination of selected trace elements, major ions and stable isotopes (18O and 2H). The chemical and isotopic features of the investigated groundwater samples suggest that they are significantly affected by fluids originated from Taftan volcano driven toward the surface by local and regional fault systems. The volcanic source is also responsible for the relatively high concentrations of As, U and V, which pose severe concerns for the quality of the water resource in the area. Distribution of As seems to be independent of pH values and the concentrations of Fe, the latter commonly forming As-adsorbing minerals, likely due to the precipitation of siderite and the occurrence of As colloids. Lack of correlation between As and SO4 seems to exclude a significant As contribution from sulfide minerals.