Sr²⁺ ions in an aqueous solution were removed using Na-A zeolites synthesized from kaolin, a natural mineral. Na-A zeolites with high crystallinity were synthesized using NaOH/kaolin mass ratios of 0.6 (ZK06) and 0.9 (ZK09). The adsorption reached equilibrium within 120 min. The adsorption data obtained from experiments for Sr²⁺ using ZK06 and ZK09 were appropriately analyzed with pseudo-second-order kinetic and Langmuir isotherm models. Comparing the maximum adsorption capacities (q_m) of ZK06 and ZK09 for Sr²⁺, the highest values were obtained at 1.90 and 2.42 mmol/g, respectively. Consequently, the Na-A zeolites synthesized from kaolin can be evaluated as adsorbents with high adsorption capacities for the removal of Sr²⁺, proportional to the degree of their crystallinity.

The radiological impact of radionuclide transport via groundwater pathways at the Wolsong Low- and Intermediate-Level Waste (LILW) Disposal Center was estimated by considering site-specific characteristics, including hydrogeology, geochemistry, and land use. Human intrusion scenarios, such as groundwater well development, were analyzed to evaluate potential pumping volumes and radionuclide migration pathways. Particular attention was given to the hydrological and geochemical aspects of radionuclide transport, with a focus on local aquifer heterogeneity, flow dynamics, and interactions with engineered barriers and surrounding rock formations that delay radionuclide migration through sorption and other retention mechanisms. Sorption coefficients (K_d), calibrated using site-specific geochemical data, were incorporated to ensure realistic modeling of radionuclide behavior. A hierarchical approach integrating scenario screening, particle tracking techniques, and mass transfer modeling was employed. Numerical simulations using FEFLOW ver. 7.3 and GoldSim ver. 14.0 software provided insights into near-field and far-field transport phenomena under well pumping conditions. The results revealed distinct spatial flux behaviors, where carbon-14 (¹⁴C) dominated near-field flux due to its high inventory, while technetium-99 (⁹⁹Tc) emerged as the primary dose contributor in the far-field flux, owing to its anionic nature and limited sorption capacity. Additionally, under high-pH conditions near concrete barriers, cellulose degradation into isosaccharinic acid was identified, enhancing radionuclide mobility through complex formation. These findings underscore the importance of site-specific sorption and speciation parameters in safety assessment and highlight the need for accurate geochemical modeling to optimize waste placement and ensure long-term disposal safety. The outcomes provide valuable insights for optimizing waste placement and contribute to the development of evidence-based safety strategies for long-term performance assessment.

Groundwater–surface water exchange is a key hydrological process that governs river water quality and aquatic ecosystems. However, the quantification of such exchange remains uncertain, especially within river island aquifers where exchange processes are highly heterogeneous. In this study, direct seepage meter measurements and indirect Darcy‐based estimates of exchange fluxes were compared under consistent spatiotemporal conditions within the aquifer of Jungsa Island, a river island in the lower West Nakdong River, South Korea. At the downstream low‐permeability site (SP‐3), Darcy‐based exchange fluxes ranged from −2.14 × 10 ⁻⁵ to 1.15 × 10 ⁻⁵ m/hr. Owing to these small magnitudes, net intrusion and discharge were not distinguishable. However, seepage meter measurements consistently indicated intrusion of surface water into the island aquifer, with fluxes ranging from −8.46 × 10 ⁻⁴ to −1.94 × 10 ⁻⁴ m/hr. At the upstream high‐permeability site (SP‐6), seepage meter measurements captured both transient groundwater discharge during short measurement periods and sustained surface water intrusion during longer measurements. Darcy‐based estimates at this site consistently indicated intrusion, indicating that both methods showed the same flow direction during longer measurements. Consequently, Darcy‐based approaches may underestimate exchange fluxes under low‐permeability conditions. These findings suggest that short‐term monitoring is favorable for capturing immediate, transient flow dynamics, whereas extended continuous measurements help buffer short‐term fluctuations to provide a more representative estimate of daily integrated exchange. Ultimately, by establishing a methodological framework that accounts for localized riverbed heterogeneity, this study provides practical guidelines for optimizing field investigation strategies in complex riparian environments.