Localized U, Ba and 226Ra geochemical anomaly in river sediments near a documented shale-gas-related waste disposal site.

Shale gas activities can release trace elements and naturally occurring radionuclides into aquatic environments, yet the long-term impact of low-intensity contamination events remains poorly constrained. This study investigates a localized geochemical anomaly observed in river sediments collected in 2021 near a documented shale-gas-related spill and waste disposal area in the Kennebecasis River watershed. Sediment cores and associated porewaters were collected to assess the distribution, potential sources, and mobility of uranium (U), barium (Ba), and radium-226 (226Ra). Results reveal localized enrichment of U and Ba near the disposal site. Elemental and radionuclide activity ratios (238U/226Ra, Th/U, Ba/Ca, and 226Ra/Ca), together with contaminant spatial distributions, are consistent with an anthropogenic source potentially associated with shale-gas-related waste disposal. Early diagenetic processes appear to promote contaminant release into porewaters, whereas transfer to the overlying water column remains limited. Distribution coefficients (Kd) and diffusive flux estimates suggest greater mobility of uranium relative to radium. Present-day diffusive flux estimates indicate limited contaminant removal by molecular diffusion. Assuming that current concentration gradients remained broadly stable through time, diffusion would account for only a few percent of the current contaminant inventory, generally less than 8%, over a 15-year period. This estimate should be regarded as a conceptual scenario rather than a reconstruction of actual attenuation history. These results highlight the value of sediment geochemistry and radionuclide tracers for identifying localized environmental anomalies potentially associated with shale-gas-related activities. Future work should include sediment dating and direct characterization of buried waste materials and associated leachates to strengthen source attribution and constrain links with the documented 2006 event.