Using apparent isotope enrichment factor to mitigate disturbances in isotopic fractionation analysis and leakage tracing by background groundwater at landfill sites across different regions

Leaking point investigation remains a pervasive challenge. In this study, an apparent isotope enrichment factor (ε_a) was proposed to mitigate disturbances on isotopic fractionation within leachate and groundwater by background waters at landfill sites across different regions. Furthermore, a leaking point tracing method was developed based on the combination of ε_a²H and ε_a¹³C-difference in dissolved carbon (ε_a¹³C_DIC-DOC), and data points from landfill sites across different regions can be used comprehensively in this method. Specifically, an ε_a²H versus ε_a¹³C_DIC-DOC plot and a redundancy analysis triplot with ε_a²H and ε_a¹³C_DIC-DOC set as the response variables were used to rigorously identify the samples indicative of leaking points in two stages. Additionally, a class kernel density estimation method was developed to quantitatively identify leaking points in these plots. To validate the isotopic tracing method, batches of physicochemical indices including isotopic indices were detected in leachate under highly anaerobic landfill conditions (LHAL), leachate that significantly interacted with background groundwater or precipitation (LBGP), leachate-contaminated groundwater (LCG), and background groundwater. Consequently, the proposed isotopic tracing method exhibited significant practicability through fully using data points from landfill sites across different regions. Differential isotopic evolution of ²H and ¹³C was observed as follows: the decrement of ε_a²H showed exceeding fourfold of ε_a¹³C_DIC-DOC after LHAL transformed into LBGP, and approximately half that of ε_a¹³C_DIC-DOC after LBGP transformed into LCG. This probably explains the distinct independence of LBGP from other water-types at landfill sites.