Analysis of groundwater dynamics in the complex aquifer system of Kazan Trona, Turkey, using environmental tracers and noble gases

The Eocene deposits of Kazan Basin in Turkey contain a rare trona mineral which is planned to be extracted by solution mining. The complex flow dynamics and mixing mechanisms as noted from previous hydraulic and hydrochemical data need to be augmented with environmental tracer and noble gas data to develop a conceptual model of the system for the assessment of the impacts of the mining and to develop sustainable groundwater management policies throughout the area. The tracers used include the stable isotopes of water (δ²H, δ¹⁸O), δ¹³C and ¹⁴C of dissolved inorganic carbon (DIC), tritium (³H), the chlorofluorocarbons CFC-11 and CFC-12, and the noble gases He and Ne. The system studied consists of three aquifers: shallow, middle, and deep. CFC data indicate modern recharge in the shallow system. The estimates of ages through ¹⁴C dating for the deeper aquifer system are up to 34,000 years. Helium concentrations cover a wide range of values from 5 × 10⁻⁸ to 1.5 × 10⁻⁵ cm³ STP/g. ³He/⁴He ratios vary from 0.09R_A to 1.29R_A (where R_A is the atmospheric ³He/⁴He ratio of 1.384 × 10⁻⁶), the highest found in water from the shallow aquifer. Mantle-derived ³He is present in some of the samples indicating upward groundwater movement, possibly along a NE–SW-striking fault-like feature in the basin.