Application of high-resolution online tracer technique in distinguishing the contaminant source of water resources in karst area: A case study of Yuquankan spring in Qianjiang county, Chongqing

The high-resolution online tracer is widely employed in hydrogeology field due to its characteristics of high precision and low cost. The pollution of the Yuquankan karst spring has caused at least 3 000 local people lack of adequate healthy drinking water. In order to find out the position of the pollution sources, the high-resolution online tracer technique was applied in the survey with fluorescein sodium and tinopal as the tracers. The results show that there is a hydraulic connection between the septic tank of a livestock breeding corporation in Chongqing and the Yuquankan karst spring. The recycle proportion of fluorescein sodium is 3.51%, 2.56% for Tinopal. The breakthrough curves of both tracers show certain differences. This phenomenon may be caused by lower solubility of fluorescein sodium compaired with Tinopal. The maximum flow velocity and mean velocity of the ground water, calculated by fluorescein sodium’s first showing time and first peak appearing time, are 27.09 m/h, 22 and 32 m/h respectively, which suggests small pores and fractures and slow percolation of pollution in the Yuquankan karst spring area. The breakthrough curves are of “multi-peak type”, so at least four groundwater channels are supposed to exist between the septic tank of the livestock breeding corporation and the Yuquankan karst spring, which reflects the uniformity of fracture development of the epikarst spring.In order to recover the quality of the Yuquankan spring water, the livestock breeding corporation must take action to prevent the leakage or be shut down as soon as possible.