Characterization of seasonal behaviors of naturally occurring radioactive materials in a groundwater borehole using an in situ monitoring system

Eunhyung Lee; MoonSu Kim; Do-Hwan Jeong; Youn-Tae Kim; Inkyu Shin; Hyemin Park; Changyong Lee; Soo-Hyung Lee; Hyun-Koo Kim

doi:10.1016/j.scitotenv.2023.165779

Characterization of seasonal behaviors of naturally occurring radioactive materials in a groundwater borehole using an in situ monitoring system

Sci Total Environ. 2023 Dec 1:902:165779. doi: 10.1016/j.scitotenv.2023.165779. Epub 2023 Jul 25.

Authors

Eunhyung Lee¹, MoonSu Kim¹, Do-Hwan Jeong¹, Youn-Tae Kim¹, Inkyu Shin¹, Hyemin Park¹, Changyong Lee¹, Soo-Hyung Lee², Hyun-Koo Kim³

Affiliations

¹ Soil and Groundwater Research Division, National Institute of Environmental Research, Incheon 22689, South Korea.
² Environmental Infrastructure Research Department, National Institute of Environmental Research, Incheon 22689, South Korea.
³ Soil and Groundwater Research Division, National Institute of Environmental Research, Incheon 22689, South Korea. Electronic address: khk228@korea.kr.

PMID: 37495147
DOI: 10.1016/j.scitotenv.2023.165779

Abstract

Understanding the temporal behaviors of naturally occurring radioactive materials is important for safeguarding groundwater as a secure water resource for drinking, agriculture, and industry usage. This study reports the vertical profiles of ²³⁸U concentration and ²²²Rn activity and the management of in situ monitoring systems during intensive field sampling of a national groundwater-monitoring borehole for seven years (2015-2021). The aim was to capture the seasonal characteristics of the ²³⁸U concentrations and ²²²Rn activity. Both factors were low in the rainy season and high in the winter season, reflecting the dilution effect of rainfall recharge. The ²³⁸U and ²²²Rn behaviors were associated with water-rock interactions of calcite dissolution in fracture zones filled with carbonate minerals. Furthermore, multilayer perceptron models estimated the ²³⁸U concentration and ²²²Rn activity with reasonable regression and classification accuracy. Hydrometeorological indicators (temperature and groundwater-level fluctuations) were more important estimators of ²³⁸U concentration and ²²²Rn activity than geochemical process indicators. The regression accuracy performance was higher at deeper sampling depths, where seasonality in the ²³⁸U and ²²²Rn behaviors dominated. From the predicted distributions of ²³⁸U concentrations and ²²²Rn activities, we could estimate the ranges of ²³⁸U concentrations and ²²²Rn activities emerging from groundwater boreholes. High exposure threats from ²³⁸U and ²²²Rn during groundwater usage were found in the winter season. When the multilayer perceptron models use the entire in situ monitoring data at refined temporal resolution, we can quickly determine the naturally occurring radioactive materials and further develop the national groundwater-monitoring borehole equipped with the in-situ monitoring system, supplementing the occasionally obtained field-measurement data.

Keywords: 222-Radon; 238-Uranium; Data-driven model; Seasonality; Water–rock interaction.