Geology topics

Research about Jeju Island

Source-linked reports with geographic coverage including Jeju Island.

3 recordsLinked to original sources

USGS2018

Comparison of groundwater age models for assessing nitrate loading, transport pathways, and management options in a complex aquifer system

In an aquifer system with complex hydrogeology, mixing of groundwater with different ages could occur associated with various flow pathways. In this study, we applied different groundwater age estimation techniques (lumped parameter model, and numerical model) to characterize groundwater age distributions and the major pathways of nitrate contamination in the Gosan agricultural field, Jeju Island. According to the lumped parameter model, groundwater age in the study area could be explained by the binary mixing of the young groundwater (4-33 years) and the old water component (>60 years). The complex hydrogeologic regimes and local heterogeneity observed in the study area (multi-layered aquifer, well leakage hydraulics) were particularly well reflected in the numerical model. The numerical model predicted that the regional aquifer of Gosan responded to the fertilizer applications more rapidly (mean age: 9.7-22.3 years) than as estimated by other models. Our study results demonstrated that application and comparison of multiple age estimation methods can be useful to understand better the flow regimes and the mixing characteristics of groundwater with different ages (pathways), hence, to reduce the risk of improper groundwater management plan arising from the aquifer heterogeneity.

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USGS2007

Evidence for terrigenic SF6 in groundwater from basaltic aquifers, Jeju Island, Korea: Implications for groundwater dating

Measurements of the concentrations of dichlorodifluoromethane (CFC-12), tritium ( 3 H), and sulfur hexafluoride (SF 6 ) in groundwater from basaltic aquifers in Jeju Island, Korea, demonstrate a terrigenic source of SF 6 . Using a lumped-parameter dispersion model, groundwater was identified as young water (<15 years), old water with negligible CFC-12 and 3 H, and binary mixtures of the two. Model calculations using dispersion models and binary mixing based on 3 H and CFC-12 concentrations demonstrate a non-atmospheric excess of SF 6 relative to CFC-12 and 3 H concentrations for more than half of the samples. The non-atmospheric excess SF 6 may have originated from terrigenic sources in relict volcanic fluids, which could have acquired SF 6 from granites and basement rocks of the island during volcanic activity. Local excess anthropogenic sources of SF 6 are unlikely. The SF 6 age is biased young relative to the CFC-12 age, typically up to 20 years and as high as 30 years. This age bias is more pronounced in samples of groundwater older than 15 years. The presence of terrigenic SF 6 can affect the entire dating range for groundwater in mixtures that contain a fraction of old water.

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USGS2006

Application of environmental tracers to mixing, evolution, and nitrate contamination of ground water in Jeju Island, Korea

Tritium/helium-3 ( 3 H/ 3 He) and chlorofluorocarbons (CFCs) were investigated as environmental tracers in ground water from Jeju Island (Republic of Korea), a basaltic volcanic island. Ground-water mixing was evaluated by comparing 3 H and CFC-12 concentrations with lumped-parameter dispersion models, which distinguished old water recharged before the 1950s with negligible 3 H and CFC-12 from younger water. Low 3 H levels in a considerable number of samples cannot be explained by the mixing models, and were interpreted as binary mixing of old and younger water; a process also identified in alkalinity and pH of ground water. The ground-water CFC-12 age is much older in water from wells completed in confined zones of the hydro-volcanic Seogwipo Formation in coastal areas than in water from the basaltic aquifer. Major cation concentrations are much higher in young water with high nitrate than those in uncontaminated old water. Chemical evolution of ground water resulting from silicate weathering in basaltic rocks reaches the zeolite–smectite phase boundary. The calcite saturation state of ground water increases with the CFC-12 apparent (piston flow) age. In agricultural areas, the temporal trend of nitrate concentration in ground water is consistent with the known history of chemical fertilizer use on the island, but increase of nitrate concentration in ground water is more abrupt after the late 1970s compared with the exponential growth of nitrogen inputs.

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