Origin and Geochemical Characterization of Groundwater from Coal Seam: A Case Study of Balasu Coalfield, Ordos Basin

The hydrochemical characteristics of groundwater are of great significance for studying the source, development, and utilization of groundwater. This study investigated the characteristics of anions and cations, total dissolved solids (TDS), hydrochemical types, and hydrogen and oxygen isotopes of surface water and groundwater in the Balasu coalfield. By conducting experiments using inductively coupled plasma emission electron spectrometry, ion chromatography, acid-base titration, and gravimetric analysis, the characteristics of ion concentration and TDS in different aquifers were analyzed to determine the possible source of groundwater in C2 (number 2 coal seam in Yan'an Formation). The Piper trilinear diagram was used to determine the hydrochemical types of aquifers, and the source of groundwater was determined based on the stable isotope characteristics of hydrogen and oxygen. The changes in ion, TDS, hydrogen, and oxygen isotopes of surface water and groundwater were analyzed, and the groundwater differences between the two sets of coal seams were compared. The research results indicate that the groundwater in C2 (number 2 coal seam in Yan'an Formation) is caused by the original sedimentary water and the infiltration of Zhiluo Formation and A1 (strata at the top of the Yan'an Formation to number 2 coal seam). However, C4 (number 3 coal seam in Yan'an Formation) is hindered by the well-developed mudstone in A3 (bottom of number 2 coal seam to the top of number 3 coal seam), which hinders the infiltration of groundwater. The study emphasizes that the overlying strata can have a significant impact on the coal seam when the moisture content is high and there is a lack of overlap, thereby promoting changes in the moisture content of the coal seam. This study provides some insights into the safety of coal mines, especially in mining areas with a high coal seam moisture content.