A study on the pollution boundary of karst groundwater system and its antifouling performance in Dabanqiao, Kunming

The Dabanqiao karst groundwater system is located at some 17 km in the east suburb of Kunming. The area belongs to subtropical plateau monsoon climate, characterised by four spring-like seasons, uneven distribution of annual rainfall, and distinct dry and wet periods. The Baoxiang river is the primary surface drainage in this system.The area extends from the northeast to the southwest. Its north and northeast are dominated by medium to low solution mountains composed of carbonate rocks, while the southwest is a sedimentary plain with flat terrain and sporadic erosion/solution monadnock.The karst aquifer system in the area mainly consists of P1y carbonate rocks. The P2e basalt, P1l clastic rocks and faults jointly constitute the impervious boundary of the system. The strikes of geological structures in the system are mainly in the direction of northwest, northeast, and north-south.This study is conducted on the basis of the geological survey project commissioned by Ministry of Land and Resources, as well as comprehensive analysis of existing results and field investigations. The objective of the study is to find out the pollution boundary of the karst groundwater system through the research of typical karst groundwater system in the Dabanqiao area; furthermore, to gain a better understanding of the karst water pollution-proof property and to lay a concrete basis for the water vulnerability assessment.The groundwater in Dabanqiao area is a typical bare-covered karst groundwater system developed in the fault basins of the eastern Yunnan area. In this paper, the groundwater pollution boundary is identified and the grades of the groundwater system is determined. The results show that the Dabanqiao groundwater system is the first-order , which consists of two subsystems, i.e. the Hengshan-Longquansi bare type subsystem and the Dabanqiao-Adicun covered one.This work determines four types of pollution boundaries ,which are the lateral boundary of the Dabanqiao karst groundwater system, top boundary of the bare area, the boundary between bare subsystem and covered subsystem and the top boundary of the covered area. And we also study the antifouling performance of the boundaries. The results show that the antifouling performance of the bare area top boundary is weak，that of the boundary between bare subsystem and covered subsystem is relatively weaker and the antifouling performance is better on top of the covered area. Through this study we can gain a better understanding of the contanmination-proof ability of the bare-covered karst groundwater system and lay an environmental hydrogeology foundation for calculating and evaluating the vulnerability of groundwater due to contamination using the model of the karst groundwater system.