Hydrogeochemical Evolution and Circulation Mechanisms of Deep Groundwater in a Complex Coal-Bearing Basin: A Case Study of the Soma–Eynez Basin, Western Türkiye

Why It Matters

Mining‑induced groundwater depletion and salinization threaten water security in the basin, demanding urgent management and regulatory action to protect limited freshwater resources.

Key Takeaways

• Deep aquifer shows Na‑Ca‑Mg‑SO₄ facies, high salinity
• Tritium values indicate residence times > decades in deep groundwater
• Mining has dropped water tables 400‑500 m, altering flow regime
• Elevated boron and sulfate limit drinking and irrigation use

Pulse Analysis

Groundwater in coal‑rich basins often evolves under the combined pressures of natural geology and intensive extraction. In the Soma‑Eynez region, the juxtaposition of a shallow volcanic aquifer and a deep karstic limestone system creates distinct hydrochemical signatures. While shallow waters retain a calcium‑bicarbonate character, the deeper confined aquifer exhibits a sodium‑rich, sulfate‑laden profile, driven by prolonged contact with Neogene sediments and the dissolution of gypsum and anhydrite. Isotopic evidence of low tritium concentrations confirms that deep waters have resided underground for decades, allowing extensive ion exchange and mineralization.

The study underscores how underground coal mining reshapes the hydrological balance. Vertical fault networks provide the primary recharge pathway for the deep aquifer, yet the relentless extraction of groundwater for mine dewatering has forced water tables down by 400‑500 meters. This drawdown not only disrupts natural flow patterns but also intensifies the concentration of dissolved solids, raising electrical conductivity to 1,000‑3,000 µS/cm. Elevated boron levels further compound the water‑quality challenges, rendering the deep groundwater unsuitable for both potable and agricultural uses under current standards.

These findings have broader implications for resource‑dependent regions worldwide. Policymakers must integrate hydrogeochemical monitoring into mining permits, enforce sustainable pumping limits, and consider artificial recharge or alternative water supplies to mitigate salinization. By linking geological processes with anthropogenic stressors, the research provides a template for assessing groundwater vulnerability in other coal basins, highlighting the need for proactive water‑resource management to safeguard ecosystems and communities.