Integrated Quantitative Tracing for Karst Groundwater Contamination: A Case Study of Landfill in Zunyi, Guizhou Province, China.

Sudden groundwater pollution in karst areas poses a serious threat to drinking water safety. Tracing contamination sources is crucial for managing and remediating groundwater pollution. Traditional tracing methods often lack accuracy, so this study combined multiple techniques to trace and quantify pollution sources near the municipal solid waste (MSW) landfill in Zunyi City, Guizhou Province, China. Analysis revealed that 83.2% of samples exceeded Chinese standards for ammonium, 81.5% for COD, and 47.9% for chloride, indicating severe pollution. To address these alarming findings, we implemented a comprehensive approach to identify and quantify the sources of contamination more accurately. First, major element geochemical tracing identified primary contamination sources. Second, trace element analysis provided more precise identification and highlighted additional sources. Third, isotopic tracing (δN-NO, δO-NO) determined types and quantities of pollution sources. Finally, long-term water quality monitoring and the PMF model enabled quantitative source apportionment of pollutants.This integrated approach found that the primary pollutants were landfill leachate (64.6%), domestic sewage (19.0%), and solute filtration from water-soil-rock interactions (16.4%). Our findings demonstrate that combining these methods enhances source resolution accuracy in aquatic environments and has the potential to be utilized in other karst regions worldwide.