Coupling Intrinsic Vulnerability Mapping and Tracer Test for Source Vulnerability and Risk Assessment in a Karst Catchment Based on EPIK Method: A Case Study for the Xingshan County, Southern China

Abstract

Amid surging population and industrial growth, there is a need to assess the vulnerability of groundwater to pollution. In this study, the case of Xingshan County in South China where karst groundwater is a major water source is presented. Field survey revealed hazardous landuse practices in highly karstified areas. To delineate areas of high vulnerability, an intrinsic vulnerability map (IVM) was created based on the EPIK (Epikarst, Protective cover, Infiltration condition, Karst network) method. Results show that 10.1, 25.8, 58.7 and 5.3% of the area are of low, medium, high and very high vulnerability. Although IVMs are powerful tools since they highlight areas of high “intrinsic” susceptibility to pollution, they do not answer the important question, “what sources are at immediate risk.” With this limitation, tracer technique was coupled with IVM to establish a link to resources/sources. Rhodamine and uranine were injected into two sinkholes in high vulnerability zones near hazardous activities. Both were detected 57.3 and 5.65 h after injection at a major spring (Bailongquan). This established link validates the IVM and highlights specific sources at risk. This study demonstrates the need to couple IVMs with tracer test in order to prioritize areas to probe in order to determine the extent of their impact by establishing active karstic groundwater flow paths. The case here is an example of source/resource vulnerability assessment, hazard/risk assessment and validation of an IVM. Our findings present a cost-effective approach to vulnerability assessment by emphasizing the reliability of EPIK method as it requires less data.