• Journal of Soil and Groundwater Environment
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• v.28 no.5
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• pp.25-35
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• 2023

This study aimed to classify spring types based on the hydrogeological characteristics of springs in Yongsu-ri~Hamo-ri coastal area in western part of Jeju Island. The springs in study area can be broadly categorized into three groups: perched groundwatrer springs (soil type), perched groundwater springs (sediment type), and basal groundwater springs. The perched groundwater springs of soil type correspond to springs where groundwater seeps out from the perched aquifer formed in the soil layer due to the development of clayey Kosan Formation beneath the surface. Because of the low hydraulic conductivity of soil layer, the average of spring discharge is less than 1 m³/day. The quality of spring water is significantly influenced by agricultural activities, resulting in high nitrate nitrogen concentrations and electrical conductivity. While the perched groundwater springs (sediment type) of the Suwolbong Tuff, which are located in the upper part of Kosan Formation, exhibited relatively higher discharge rates, their water quality was similar to soil-type springs. Basal groundwater springs are located in the zone of basal groundwater, mostly near the coastline. This type of spring appears to discharge of up to 3,707 m³, and the salinity content varies with the tidal fluctuations, especially increasing significantly during dry seasons.

• Journal of the Korean Society of Groundwater Environment
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• v.1 no.1
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• pp.33-50
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• 1994

The Hydrogeologic data of 455 water wells comprising geologic log and aquifer test were analyzed to determine hydrogeologic characteristics of the Cheju island. The groundwater. of the Cheju island is occurred in unconsolidated pyroclastic deposits and crinker interbedded in highly jointed basaltic and andesic rocks as high level, basal and parabasal types under unconfined condition. The average transmissivity and specific yield of the aquifer are at about 29,300㎡/day and 0.12 respectively, The total storage of groundwater is estimated about 44 billion cubic meters. Average annual precipitation is about 3,390 million ㎥ among which average recharge is estimated for 1,494 million ㎥ being equivalent 44.1% of total annual precipitation with 638 million ㎥ of runoff and 1,256 million ㎥ of evapotranspiration. Based on groundwater budget analysis, the sustainable yield is about 620 million ㎥(41% of annual recharge)and rest is discharging into the sea. The geologic logs of recently drilled thermal water wells indicate that very low-permeable marine sediments(Sehwa-ri formation) composed of loosely cemented sandy silt derived from mainly volcanic ashes at the 1st stage volcanic activity of the area is situated at the 120${\pm}$68m below sea level. Another low-permeable sedimentary rock called Seogipo-formation which is deemed younger than the former marine sediment is occured at the area covering north-west and western part of the Cheju island at the ${\pm}$70m below sea level. If these impermeable beds art distributed as a basal formation of fresh water zone of the Cheju island, the most of groundwater in the Cheju island will be para-basal type. These formations will be one of the most important hydrogeologic boundary and groundwater occurences in the area.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1994.07a
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• pp.184-215
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• 1994

The Hydrogeologic data of 455 water wells comprising geologic and aquifer test were analyzed to determine hydrogeoloic characteristics of Cheju island. The groundwater of Cheju island is occurred in unconsolidated pyroclastic deposits interbedded in highly jointed basaltic and andesic rocks as high level, basal and parabasal types order unconfined condition. The average transmissivity and specific yield of the aquifer are at about 29,300m$^2$/day and 0.12 respectively. The total storage of groundwater is estimated about 44 billion cubic meters(m$^3$). Average annual precipitation is about 3390 million m$^3$ among which average recharge amount is estimated 1494 million m$^3$ equivalent 44.1% of annual precipitation with 638 million m$^3$ of runoff and 1256 million m$^3$ of evapotranspiration. Based on groundwater budget analysis, the sustainable yield is about 620 million m$^3$(41% of annual recharge)and rest of it is discharging into the sea. The geologic logs of recently drilled thermal water wens indicate that very low-permeable marine sediments(Sehwa-ri formation) composed of loosely cemented sandy sat derived from mainly volcanic ashes, at the 1st stage volcanic activity of the area was situated at the 120$\pm$68m below sea level. And also the other low-permeable sedimentary rock called Segipo-formation which is deemed younger than former marine sediment is occured at the area covering north-west and western part of Cheju at the $\pm$70m below sea level. If these impermeable beds are distributed as a basal formation of fresh water zone of Cheju, most of groundwater in Cheju will be para-basal type. These formations will be one of the most important hydrogeologic boundary and groundwater occurences in the area.

• Economic and Environmental Geology
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• v.24 no.3
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• pp.319-327
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• 1991

Cheju is the biggest island in Korean peninsula, consisted entirely of volcanic rocks and pyroclastic sediments. The topography is characterized by wide basalt plain in the low altitude but at the center of island, basalt volcano rises 1,950m above sea-level. Surface drainage is very poor, therefore water supply has been dependent on ground water and natural springs. There are about 1,650 production wells and most of them yield $1,000{\sim}2,000mm^3/day$. According to increase of ground water use, saline water is intruded in the low altitude of coastal area. Specially in the eastern coastal area, the topography is extensively flat and the level of ground water is very close to sea-level, at which overuse of ground water has brought saline intrusion up to maximum 6km far from the coast. Hydrochemical monitoring on this salt water intrusion is now undertaken on long term base.

• Journal of Soil and Groundwater Environment
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• v.12 no.4
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• pp.60-71
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• 2007

Groundwater from public wells was monitored during one year with two month interval for hydrogeochemical parameters and chlorofluorocarbons (CFCs) as environmental tracers in Jeju Island. Concentrations of major cations and $SiO_2$ show variation less than 10% whereas $NO_3$ and dissolved oxygen (DO) showed larger variation though DO variation did not change oxic or suboxic condition. $NO_3$ concentration has no consistent seasonal pattern with the largest variation of 35%. Groundwater ages determined by CFCs became temporarily younger by 5 years in October for groundwater with ages of 15 to 25 years, which can be attributed to infiltrating water in rainy season. Compared to air temperature, groundwater temperature has much smaller variation with no phase difference, which can be accounted for by a two-component model consisting of infiltrating water from surface and deeper groundwater with negligible temperature variation. The relatively small variation in groundwater age and temperature indicates that groundwater recharge through fast flow-paths is much smaller compared with basal groundwater in terms of aquifer storage.