This study conducted two column experiments simulating organic matter-based permeable reactive barriers (PRBs) for nitrate removal from groundwater. The columns used woodchips as the reactive material: one had been operated for approximately nine years (Old column), and the other was newly constructed for this study (New column). Nitrate removal performance was evaluated by comparing denitrification rates and assessing isotopic fractionation characteristics (δ¹⁵N-NO₃⁻, δ¹⁸O-NO₃⁻, δ²H-H₂O, and δ¹⁸O-H₂O). Changes in pH, alkalinity, Eh, dissolved oxygen (DO), and N₂ gas production suggested that geochemical conditions were favorable for denitrification. Calculation of denitrification rates (New: 1.3 mmol L⁻¹ day⁻¹; Old: 0.08 mmol L⁻¹ day⁻¹) indicated that reactivity was retained even after long-term operation, demonstrating the long-term feasibility of woodchips for PRBs. As nitrate concentrations decreased, δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻ values increased from 8.27‰ to 27.13‰ and 19.81‰ to 39.08‰, respectively, with a 1:1 enrichment factor ratio typical of denitrification. On the other hand, no significant δ¹⁸O-H₂O changes were observed. The findings from this study may support future research on isotopic fractionation during nitrogen transformations and its linkage to hydrological processes. The results may also serve as a quantitative reference for field-scale PRB design and performance assessment.

Keywords: Nitrate, Column test, Permeable reactive barrier, Denitrification rate, Isotopic fractionation