Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Geological investigations within the Turów open-cast mine expansion impact assessment on groundwaters of Hrádek and Frýdlant regions: a progress report
Published online: 12 October 2020
AbstractStarting from autumn 2016, the Czech Geological Survey has been focused on assessing the impact of planned extension of the Turów coal mine, an extensive open-cast mine located in the eastern part of the Zittau Basin (Lower Silesia, Poland). In particular, we aimed on possible effects on groundwater regime in the adjacent Czech part of the Zittau Basin, the Hrádek sub-basin, and in the borderland Frýdlant area. The Hrádek sub-basin is filled by Tertiary deposits with coal covered in the eastern part by up to 80 m thick Quaternary, predominantly glaciofluvial deposits. In the Frýdlant area, the Tertiary deposits form outliers further NE of the Zittau Basin and are largely covered by the Quaternary glaciofluvial deposits, up to 20-60 m thick. The glaciofluvial deposits (porous, quartzose sands and sandy gravels, locally well-sorted) form an important aquifer in the study area. It was assumed that the extension of the Turów coal mine could affect not only the Tertiary aquifers, but also Quaternary glaciofluvial aquifer. This could take place in particular areas where aquifers in upper part of the Tertiary communicate in terms of groundwater flow with the Quaternary glaciofluvial aquifer. This assumption could have been confirmed only by a detailed investigation of the study area’s geological setting.
Geological investigations have been conducted in several consecutive stages: (1) Processing of all available borehole data from CGS archives and database provided by the Polish Energy Group. In addition, construction of cross-sections provided first insight into geological setting of the study area. (2) Constructing basic 2D contour-line model of main stratigraphic surfaces - top of the basement, base of the Tertiary, bases and tops of the Tertiary coal seams (Cb1, Cb2 and Cb3), base of the Quaternary. Where database did not allow higher resolution, the interpreted geological setting in the resulting model allowed for groundwater flow towards Polish territory. The critical localities without borehole data were selected for field geophysical measurements in the subsequent stage. (3) Field geophysical measurements (in-house ERT). In total, 70 ERT profiles were measured throughout the study area. (4) Construction of the tectonic framework of the study area (cf. Václ 1998). (5) Update of the 2D contour-line model by implementing new geophysical data (ERT profiles, gravity maps). (6) Complex geophysical measurements (VES and seismic profiles) carried out by Geonika, a. s., at the localities selected as a result of geological modeling.
The main result of the geological part of this project is providing a detailed knowledge of the geological setting of the borderland Hrádek and Frýdlant regions. This was possible by integrating archive as well as newly acquired data into the geological model that would serve as a basis for groundwater modeling and hydrogeological/hydrological balance. The geological model is focused on displaying regional extent and thickness of sedimentary units-carrying the principal groundwater aquifers-represented in the study area by the Tertiary and Quaternary strata (mainly glaciofluvial deposits).
In the upcoming stage of the project, a series of exploratory boreholes planned since the spring 2018, is going to be drilled. Geological (cored) as well as hydrogeological boreholes (wells) will serve as a valued database for an ultimate update of the geological model presented herein.
Published online: 12 October 2020