This study investigates and analyzes the major characteristics of naturally occurring asbestos (NOA) in the Seosan area, based on a geological map of NOA distribution. The study area includes Daesan-eup, Seokmun-myeon, and Palbongmyeon in Seosan-si, Chungcheongnam-do, South Korea, with 32 samples collected from nine sites. The asbestos-containing rocks primarily consist of dolomite, limestone, calcareous silicate rock, and marble, most of which exhibit a mass-fiber morphology. While the weathering grade of the outcrops is generally within level 3, some areas show higher weathering levels (grade 4), indicating potential risks of asbestos dispersion into the air. The collected samples were analyzed using polarized light microscopy (PLM), X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and transmission electron microscopy with energy-dispersive spectroscopy (TEM-EDS). The primary asbestos types identified were tremolite and actinolite asbestos of the amphibole group, with anthophyllite asbestos detected in some locations. Notably, certain asbestos-containing rocks were found near coastal areas and docks, highlighting the need for continued monitoring in the event of future development activities.

Deep borehole drilling is essential not only to select the host rock type for deep geological disposal of high-level radioactive waste (HLW), but also to identify the characteristics of the disposal site during the site selection process. In particular, since the disposal depth of HLW is considered to be over 300 m, deep borehole drilling must be performed. In deep borehole drilling, drilling design, excavation, and operation may vary depending on the rock type, drilling depth, and drilling purpose etc. This study introduced cases in which Korea was divided into four geotectonic structures and four representative rock types and conducted with a goal of 750 m drilling depth. Prior to this, a review of deep drilling cases conducted at domestic and abroad was presented. If sufficient time and cost are available, several drilling holes can be excavated for various purposes, but if not, one or two drilling holes should be used to achieve the objectives of various fields related to HLW disposal. The presence of bedding, strata or fault zones depending on the type of rock, etc. may affect drilling deviation or circulating water management. In addition, unlike drilling in general geotechnical investigation drilling, the use of polymers or grouting agents is limited to determine hydraulic and geochemical characteristics. This report introduces the experience considered during the design and drilling process of deep drilling in granite, gneiss, sedimentary rock, volcanic rock, etc., and is expected to be used as basic data when carrying out future HLW projects.