Présentations Colloques

    Oral Presentation
    ORPHAN
    ORPHAN PRESENTATIONS
    Kovacs Attila
    Consequences of mine depressurisation on a regional carbonate aquifer, Tata, Hungary
    Mine dewatering operations in the Transdanubian Mountains, Hungary between 1960 and 1990 caused significant groundwater depressurisation and the vanishing of significant karst springs in the regional carbonate aquifer. Following the termination of mining operations, the flow system started to recover and karst springs are reappearing. The reactivating springs cause environmental and engineering problems. The aim of the present study was to characterise the recovering flow system, to delineate affected areas and to provide predictions on the location and timing of spring reactivation. **In order to investigate future hydrogeological conditions, geological assessment, piezometric and spring discharge measurements, hydrograph analysis and hydrochemical analysis were undertaken. **Spring locations are aligned with deep tectonic structures both in uncovered and confined aquifer zones. The analysis of well hydrographs indicates that there is no hydraulic connection between shallow and deep groundwater bodies. The analysis of recovery curves suggests that equilibrium groundwater level will be reached within a few years from the time of the analysis. **The chemical composition of most reactivating springs indicates karst water origin. Some springs discharge shallow groundwater and show signs of local pollution. Geochemical data indicates significant changes in karst water chemistry in response to groundwater depressurisation and the following recovery. While bicarbonate concentration decreased, sulphate concentration increased during mine dewatering operations. Recent hydrochemical data indicates the delayed rebound of main water component concentrations, suggesting the geochemical recovery of the groundwater system. **A further increase of piezometric levels and reappearance of karst springs along tectonic features are expected to impact on built-up areas. Reactivating karst springs will facilitate the reconstruction of parklands and baths and will positively influence the revival of groundwater dependent ecosystems.**

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