Karst collapse columns, as a potential water passageway for mine water inrush,
are always considered a critical problem for the development of deep mining techniques.
This study aims to identify the mixing process of groundwater deriving two different limestone
karst-fissure aquifer systems. Based on analysis of mining groundwater hydrogeochemical properties,
hydraulic connection between the karst-fissure objective aquifer systems was revealed. In this paper,
piper diagram was used to calculate the mixing ratios at different sampling points in the aquifer
systems, and PHREEQC Interactive model (Version 2.5, USGS, Reston, VA, USA, 2001) was applied
to modify the mixing ratios and model the water–rock interactions during the mixing processes.
The analysis results show that the highest mixing ratio is 0.905 in the C12 borehole that is located
nearest to the #2 karst collapse column, and the mixing ratio decreases with the increase of the
distance from the #2 karst collapse column. It demonstrated that groundwater of the two aquifers
mixed through the passage of #2 karst collapse column. As a result, the proposed Piper-PHREEQC
based method can provide accurate identification of karst collapse columns’ water conductivity,
and can be applied to practical applications.