Environmental geochemistry and sources of natural arsenic in the Kharaqan hot springs, Qazvin, Iran

The Kharaqan hot springs are located in the historic city of Abe-Garm, famous for its hot springs, in Qazvin province, in northwestern Iran. Thermal waters with temperatures ranging from 28.7 to 52 °C vary in chemical composition and TDS contents. Those waters generally are enriched in Na–Cl–HCO₃ and suggest deep water circulation. Chemistry of all of the water samples are graphed in the Cl–SO₄–HCO₃ ternary diagram. There is a trend of mixing along a line of constituent proportions between recently recharged water and older water. The trend toward the chloride corner is mainly the result of contact in the subsurface with evaporite-bearing formations and/or mixing with brines. Relatively high concentrations of Na, Ca, K, Cl, and SO₄ resulted from rock/water interactions. These hot spring waters show high concentrations of arsenic (0.14–0.95 mg L⁻¹). The diffusion of As-bearing spring waters into shallow aquifers could contaminate the groundwater which is used for drinking purposes. Also discharges of this As-enriched water into streams and rivers could affect irrigated crops in downstream fields. In both cases, the health of local residents could be at risk.