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Open AccessArticle

A Borehole-Based Approach for Seawater Intrusion in Heterogeneous Coastal Aquifers, Eastern Part of Jeju Island, Korea

by Jehyun Shin 1 and Seho Hwang 1,2,*
1
Groundwater Research Center, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea
2
Department of Petroleum Resources Technology, University of Science & Technology, Daejeon 34113, Korea
*
Author to whom correspondence should be addressed.
Water 2020, 12(2), 609; https://doi.org/10.3390/w12020609
Received: 16 January 2020 / Revised: 20 February 2020 / Accepted: 21 February 2020 / Published: 24 February 2020
(This article belongs to the Section Hydrology and Hydrogeology)
Understanding the basaltic aquifer system and seawater intrusion on the volcanic island of Jeju, Korea, has received significant attention over the years, and various methodologies have been suggested in the contributions. Nevertheless, it is still difficult to effectively characterize groundwater systems due to the long period of volcanic activity and the lithological variability of basalt. In this study, geophysical well logging in seawater intrusion monitoring boreholes detected a sudden decrease of electrical conductivity within the saltwater zone in the eastern part of Jeju Island. This anomalous condition cannot be explained by the Ghyben-Herzberg model, which has historically been considered as the basic groundwater model of Jeju Island. This paper focuses on fine-scale temporal and spatial variability of groundwater flow using electrical conductivity and temperature logs and borehole temperature monitoring by a thermal line sensor. On the basis of the results, we evaluate an alternative model to replace the traditional conceptual model in the eastern part of Jeju Island. It is revealed that the area consists of heterogeneous aquifer systems, and the behavior of freshwater and saltwater is understood by temperature monitoring over the entire depth of boreholes. Coastal aquifers flow through two or more independent channels with weak vertical connections. In addition, seawater intrusion does not occur continuously in the vertical direction from the bottom depth, but instead occurs through these multilayered aquifers. In particular, the multilayered aquifers that are responsible for flow pathway, as well as the freshwater–saltwater interface form mainly at lithological boundaries. Our preliminary conceptual model is expected to be improved and revised by various measurements of hydrodynamic parameters such as flowmeter or packer test. View Full-Text
Keywords: basaltic aquifer; seawater intrusion; electrical conductivity and temperature logs; borehole temperature monitoring; thermal line sensor basaltic aquifer; seawater intrusion; electrical conductivity and temperature logs; borehole temperature monitoring; thermal line sensor
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Shin, J.; Hwang, S. A Borehole-Based Approach for Seawater Intrusion in Heterogeneous Coastal Aquifers, Eastern Part of Jeju Island, Korea. Water 2020, 12, 609.

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