This study investigated the long-term persistence of drilling waste (DW) in unconsolidated deep-sea sediments of the Ulleung Basin three years after gas hydrate drilling at Site UBGH2-6. Seafloor imagery, sediment cores, in-situ hydrographic observations, HYCOM simulations, and multi-proxy geochemical analyses (210Pbex, TOC, TN, CaCO3, Ba, Ca, Ti, Mn, and Fe) were integrated to evaluate DW preservation. A light-colored DW deposit remained within a ∼ 10 m radius of the borehole with an average thickness of ∼6.5 cm under persistently weak bottom-current conditions. A first-order estimate indicates a theoretical DW production of ∼14.0 m3, whereas the larger deposit volume (∼20.4 m3) reflects limited redistribution minor contributions from adjacent boreholes. Disturbed 210Pbex profiles and characteristic geochemical signatures demonstrate burial of the original seafloor and distinguish carbonate-rich drill cuttings from barite-rich drilling mud. These findings provide a quantitative framework for assessing DW accumulation, dispersal, and environmental impacts associated with offshore energy exploration.
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