Application of the numerical simulation method in concealed karst wellhead for protection area delimitation and contamination prevention

LI Xing-yu; NAN Tian; WANG Xin-juan; LI Peng; XIE Zhen-hua; SHAO Jing-li

Abstract：A wellhead protection area (WHPA)is an effective technical method and basic standard for safe-guardking groundwater resources.Frequently-used methods for WHPA delimitation include the empirical approach,analytical methods,tracing tests and numerical simulation.Of these,numerical simulation is pre-ferred for complicated hydrogeological conditions.It is quite difficult to use numerical simulation methods in WHPA delimitation for a concealed karst aquifer,as a result of its heterogeneity,anisotropy,parameter un-certainty and development under Quaternary or other bedrock.This study takes two groundwater sources, Daxing Niantan wellhead and Tongzhou Longwangzhuang wellhead,which are located in the concealed karst system southeast of Beijing,as examples to study the numerical simulation method of WHPA delimitation. The numerical simulation model,which takes the three-dimensional transient flow of Quaternary and karst aquifer into consideration,is established by the GMS.Then particle tracing technology is used to confirm the WHPA,taking a tracing time of 100 days as the primary protection zone and 1,000,days as the secondary protection zone.Related pollution-control measures are proposed according to the WHPA results.Addition-ally,given that leakage from the overlying Quaternary loose-porosity aquifer is the primary recharge source for the concealed karst aquifer,the boundary of the Quaternary WHPA is as the same as the boundary of the karst WHPA.Control of the Quaternary water contamination needs to be enhanced to prevent pollution of the karst water.