• 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.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.61-64
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• 2005

The calculated characteristics of groundwater within the Youngsan river basin are : casing depth-17.1m, well depth-74.8m, natural water-2.6m, pumping water-43.9m, yields-391$m^3/D$, transmissivity-16.3$m^3/D/m$, storativity-0.068. As far as hydrogeological units are concerned, in casing depth, weathered granites are deepest followed by gneiss, volcanics, and sediments. In major aquifer development areas, sediments are deepest followed by volcanics, granites and gneiss in more shallow areas, Altogether, the major aquifar development depth of the Youngsan river basin is within the $35{\sim}60m$ range.

• Journal of the Speleological Society of Korea
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• no.67
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• pp.43-51
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• 2005

This study on Gobongdond Wetlands have hydrogeomorpholosic charateristics in the southern-west of Gogongsan. This study area have been dissected and deep weathered. in geology, this area show banded gneiss consisting of alternated felsis and mafic layers. in geomorphology this area have 3 slope that surplyed the surface water and ground water, but have a little water source by surface water. The most of Gobongdong wetland's water sources are aquifer or confined aquifer, so this wetlands have many seepages or discharges. The characteristics of Soil have retained the wetland's water. Deep weathering made the parents soil into clay minerals.(siallitization) This clay minerals have a high water table.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.409-411
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• 2008

Water conveyance from waste water treatment plant can play a role in securing river water quantitatively in urban watershed, but it can also cause more severe contamination of river water due to lack of water quality management. Soil aquifer treatment(SAT) has been introduced to overcome the worsening water quality in the water conveyance system considering the characteristics of Korean urban watershed. The application of SAT to the water conveyance system not only improve water quality of ordinarily discharged water but also prevent accidential water pollution to the urban watershed. Since most domestic urban watersheds are consist of narrow terrace lands and surrounded by roads, SAT is estimated not to be appropriate to the urban watershed with respect to the quantitative efficiency. However, since the upstream of urban watershed in which discharge ports are located usually consists of agricultural lands, SAT can be applied near discharge ports. Therefore, combination of water conveyance and SAT is expected to supply clean and safe river water in urban watershed.

• The Journal of Engineering Geology
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• v.22 no.1
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• pp.27-37
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• 2012

To investigate the effect of aquifer disturbance on hydraulic properties while well drilling at unconsolidated aquifer, the following tests were conducted: the surge block and air-surging methods, which are well development methods used after well drilling; and step-drawdown tests and constant-rate pumping tests, which are used to assess changes in the aquifer after well drilling and development. The result of step-drawdown tests indicated that drawdown for a pumping-rate of $700m^3/day$ was 21.62 m after well development, decreasing 4.39 m from 26.01 m after well drilling. The skin factor used to identify the well properties decreased from 7.92 after well drilling to 5.04 after well development, respectively, which shows the improvement of well. Constant-rate pumping tests revealed a small increase in aquifer transmissivity after well development at MW-2, -3, and -4, centering around pumping well, from $1.684{\times}10^{-3}{\sim}4.490{\times}10^{-3}m^2/sec$ to $4.002{\times}10^{-3}{\sim}4.939{\times}10^{-3}m^2/sec$. MW-1, however, showed decline in hydraulic conductivity from $1.018{\times}10^{-2}m^2/sec$ to $6.988{\times}10^{-3}m^2/sec$, which was caused by a small decrease of aquifer permeability around monitoring well MW-1 due to latent factor of air interception and clogging in aquifer during surging. This finding indicates that fine particles have an effect on hydraulic properties at unconsolidated aquifers during well drilling; therefore, we consider that well drilling and development have an effect on hydraulic properties.

• Journal of Environmental Science International
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• v.18 no.9
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• pp.1017-1026
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• 2009

In Jeju island, the surface runoff characteristics are quite different from those of inland. Most of streams show dried characteristics by means of large portion of recharge which goes to the deep aquifer. For this reason, the accurate estimation of hydrologic components by using watershed model like SWAT is very difficult. On the other hand, the integrated SWAT-MODFLOW model is able to simulate the complex runoff structure including stream-aquifer interaction, spatial-temporal groundwater recharge and so on. The comprehensive results of Pyoseon region in Jeju island show that the amount of groundwater discharge to stream is very small, but it might be added to the discharge into the sea. Statistical analysis shows that SWAT-MODFLOW's results represent better than SWAT's. Also, SWAT-MODFLOW produces a reasonable water budget which shows a quite similar pattern of observed one. This result proves that the integrated SWAT-MODFLOW can be used as a proper tool for hydrologic analysis of entire Jeju island.

• Journal of the Mineralogical Society of Korea
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• v.26 no.2
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• pp.129-138
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• 2013

River bank filtration has been considered as a promising alternative water management scheme, in which groundwater is extracted from an aquifer near a river after infiltration of the river water into the aquifer, thereby improving and maintaining the quality of water recovered. Iron (Fe) associated with sediment in contact with groundwater and infiltrating surface water is an important factor in determining the quality of water recovered from the pumping wells in river bank filtration. This study reports the results of Fe speciation in the aquifer sediment samples collected from different depths at the river bank filtration site in Changwon, studied using four different chemical extraction methods, namely, ferrozine, oxalate, HCl, and DCB methods. Overall, the results show that Fe(II) as well as the total Fe content decreases with depth down to ~20 m and then increases further below. This trend is consistent with the redox characteristics suggested by visual observation. The silt/clay size fraction (${\phi}$ < 62.5 ${\mu}M$) has up to 2~10 times more Fe compared with the sand size fraction (62.5 ${\mu}M$ < ${\phi}$ < 2 mm), depending on the extraction method. Of the four extraction methods, DCB solution extracted the most Fe from the sediment samples. The amounts of Fe extracted by the different extraction methods can be a good indicator of the redox conditions along the depth of the aquifer.

• Geophysics and Geophysical Exploration
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• v.9 no.3
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• pp.225-230
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• 2006

Fluid replacement and conductivity logging have been applied to three boreholes in coastal aquifer in order to identify permeable fractures and to estimate the origin of saline groundwater. Fluid replacement technique measures and monitors the change of borehole fluid conductivity with depth under ambient or pumping condition after replacing the original borehole fluid with different one (by pumping out original one and injecting simultaneously new one at the hole bottom). After the replacement of borehole fluid, the change of fluid conductivity can be the direct indicator of the intake flow of formation water through aquifer such as permeable fractures or porous formations. The conductivity profiles measured with times therefore indicate the locations of permeable zone or fractures within the open hole or the fully slotted casing hole. As a result of fluid conductivity logging for three boreholes at coastal area in Yeonggwang, Jeonam Province, it is interpreted that the seawater intrusion in this area is not by remnant saline groundwater after land reclamation but mainly by intrusion of saline water through fractured rock. This approach might be useful for assessing the characteristics of seawater intrusion, the design of optimal pumping, the mitigation of seawater intrusion using freshwater injection, and estimating the hydraulic characteristics in coastal aquifer.

• Economic and Environmental Geology
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• v.54 no.6
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• pp.699-707
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• 2021

Hwajinpo Lagoon, located on the eastern coast of Korea, is a unique environment where freshwater and saltwater are mixed. Systematic management of the lagoon is required because it is a biodiversity-rich and area of high conservation value. The existing environment of the lagoon was evaluated by identifying the distribution of the groundwater level and groundwater flow characteristics. In addition, hydrogeochemical fluctuations were analyzed to determine the effect of seawater intrusion into the aquifer. The results demonstrate that the freshwater-saltwater interface is distributed throughout the aquifer and rises when water of the lagoon evaporates due to prolonged periods of low rainfall and high temperature, thereby increasing the possibility of seawater inflow through groundwater. As for the ionic delta properties (difference between the measured and theoretical concentration of mixed waters), it was estimated that the cation-exchange and precipitation reactions occurred in the aquifer due to seawater intrusion. The ratio of seawater mixed at each point was calculated, using oxygen isotopes and chloride as tracers, resulting in an average of 0.3 and a maximum of 0.87. The overall seawater mixing ratio appears to be distributed according to the distance from the coast. However, some of the results were deviated from the theoretical expectations and reflected the characteristics of the nearby aquifers. Further research on seasonal changes and simulation of seawater intrusion mechanisms is required for specific analysis.

• Economic and Environmental Geology
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• v.27 no.3
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• pp.295-311
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• 1994

A comprehensive in-situ tests are performed to define the hydrogeologic and hydrodispersive characteristics such as hydraulic conductivities, longitudinal dispersivity, and average linear velocities as well as conducting flow-net analysis at the study area. The results show that the study area is very heterogeneous so that hydraulic conductivities range from $6.45{\times}10^{-7}$ to $1.15{\times}10^{-5}m/s$ with average linear velocities of 0.34~0.62m/day. Whole groundwater in upper-most aquifer is discharging into the sea with specific discharge rate of $7.2{\times}10^{-3}$ to $1.3{\times}10^{-2}m/day$. The longitudinal dispersivity of the aquifer is estimated about 4.8m through In-situ injection phase test. The area is highly vulnerable to potential contaminant sources due to it's high value of DRASTIC index ranging from 139 to 155 and also under water table condition with very shallow groundwater level. To delineate contaminant plumes of toxic NaOH and carcinogenic benzene when these substances are assumed to be leaked through existing TSDF at the study area by unexpected accidents or spill, Aquifer Simulation Model (ASM) including Flow and Transport Model is used. Te simulated results reveal that the size of NaOH plume after 5 years continuous leak is about $250{\times}100m$ and benzene after 10 years, $490{\times}100m$. When the groundwater is abstracted about 50 days, which is maximum continuously sustained no-precipitation period during 30 years, with pumping rate of $100m^3/day$, THWELL program shows that the groundwater is adversly affected by sea water intrusion.