Tracer test and analysis of groundwater system in a karst area of southwest China

The study area is located in a karst area of Sichuan Province in southwest China. It hosts intense karst development and complex hydrogeological conditions, where underground karst forms include caves, fissures and conduits. Taking this typical karst area as an example, this paper analyzes the application of tracer tests in karst conduit connectivity and acquisition of hydrogeological parameters, analyzes the karst groundwater runoff regular pattern, and estimates the structural characteristics and hydrogeological parameters of karst underground aquifers. These data will facilitate rapid and accurate determination of the scope of groundwater recharge, analyzing the causes of spring discharge cutoff and pollution, and providing a basis for spring protection. First, a sinkhole is selected as the release point, and the groundwater dew point is taken as the receiving point to judge the actual direction of the underground runoff and the hydraulic relation from the west side and the east side of sinkhole respectively. A quantitative analysis of breakthrough curves of the tracers is carried out by Qtracer2, and the tracer recovery rate, average groundwater velocity, maximum velocity, structural characteristics and hydrogeological parameters of the karst conduit are determined. The results show that there is no direct hydraulic relation between the sinkhole and the receiving points JS01 and JS03. While there is a hydraulic link between the sinkhole and the receiving point JS02, where the karst conduit extremely developed, the aquifer medium is uneven, and the groundwater movement path is relatively smooth, which is a typical turbulent flow state. The main direction of the underground runoff of the sinkhole is from west to east. In the period of heavy rainfall during the wet season, the point JS04 can receive sodium fluorescein, indicating that the underground water level increases during the wet season, which will lead to discharge of partial water volume to the west side of the sinkhole.