• Journal of the Korean earth science society
• /
• v.28 no.4
• /
• pp.478-490
• /
• 2007

With groundwater data of seawater intrusion monitoring network in coastal areas of Korea's main land, we analyzed types of seawater intrusion through the coastal aquifer. The data including groundwater level, temperature and electrical conductivity obtained from 45 monitoring wells at 25 watershed regions were evaluated. Based on statistical analysis, correlation analysis and variation type analysis, groundwater levels were mainly affected by rainfall and artificial pumping. About 78% of the monitoring wells showed average temperature higher than $15^{\circ}C$ and about 58% of them showed minimum variations less than $0.2^{\circ}C$. Electrical conductivities showed a large magnitude of variation and irregular characteristics compared with groundwater levels and temperatures. Average electrical conductivities lower than $2,000\;{\mu}S/cm$ were observed at 28 monitoring wells while those of higher than $10,000\;{\mu}S/cm$ were done at 9 monitoring wells. From the cross-correlation analysis, groundwater levels were mostly affected by precipitation while temperature and electrical conductivity showed very low correlation. Meanwhile tidal variations strongly affected the groundwater levels comparing to precipitation. We classified the long-term monitoring data according to variation types such as constant process, linear trend, cyclic variation, impulse, step function and ramp. Impulse type was dominant for variations of groundwater level, which was largely affected by rainfall or artificial pumping, the constant process was dominant for temperature. Compared with groundwater level and temperature, electrical conductivities showed various types like linear trend, step function and ramp. According to the discrepancy of variation characteristics for monitoring data at each well in the same region, periodical analysis of monitoring data is essentially required.

• The Journal of Engineering Geology
• /
• v.24 no.2
• /
• pp.283-295
• /
• 2014

Groundwater monitoring wells are important to maintain their performance for long term monitoring. The monitoring wells with extensive internal incrustation by clay adsorption were selected for this study. The performance of these monitoring wells was improved by pump washing, tube replacements for dedicated samplers, and well surging. After each improvement, the Mg, Mn, and Zn concentrations were increased. The results show that under these conditions, the monitoring wells must be carefully inspected at least once a year. Even in the case of no abnormal phenomenon like as internal incrustation, the monitoring wells need to be serviced at least once every four to five years to guarantee that they are effectively monitoring groundwater quality.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.37 no.6
• /
• pp.981-987
• /
• 2017

Jeju Island is a volcanic island which has a large permeability. Groundwater is a major water resources and its proper management is essential. Especially, there is a multilevel restriction due to the groundwater level decline during a drought period to protect sea water intrusion. Preliminary countermeasure using long-term groundwater level prediction is necessary to use agricultural groundwater properly. For this purpose, the monthly groundwater level prediction technique by Artificial Neural Network model was developed and applied to the representative monitoring wells. The monthly prediction model showed excellent results for training and test periods. The continuous groundwater level prediction model also developed, which used the monthly forecasted values adaptively as input data. The characteristics of groundwater declines were analyzed under extreme cases without precipitation for several months.

• Economic and Environmental Geology
• /
• v.44 no.3
• /
• pp.239-246
• /
• 2011

Groundwater in small islands is used as main water resource but the overuse of groundwater may cause seawater intrusion and temperature decrease in geothermal wells. This study aimed to characterize the hydrogeology of Maeum-ri area in Seokmo Island of Ganghwagun using long-term monitoring at groundwater wells and geothermal wells. In the monitoring period seasonal water level change, consistent drop or increase of water levels are not detected. The groundwater temperature about 10m below ground surface shows year cycle variation having two to five months difference with ambient temperature cycle. The storativity was calculated by tidal method. The storativity estimated by adapting tidal efficiency factor showed some larger values than that by using tidal time lag. The result suggested that the tidal method assuming several assumptions on aquifer condition may produce broad ranges but the calculated ranges at this application are reasonable. The similar shape of groundwater level change and tidal effects was observed at several wells clustered east-south-east direction which may implicate the distribution of vertical fracture system strongly related with groundwater flow channels. The applied methodology and study results will bc valuable to evaluate optimal pumping rate for the preservation of groundwater resources, and to manage geothermal development.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.57 no.1
• /
• pp.25-35
• /
• 2015

As livestock manure treatment is becoming a problem, manure application in forest plantation is recommended as an alternative. In this study, to investigate the impact due to liquid manure application in forest plantation, soil, soil water and shallow groundwater quality had been monitored in poplar experimental site where the liquid manure (LM) was applied. Water samples were collected weekly during growing season (April to October) from 2008 to 2011. From the monitoring results, phosphorus concentration in the soil and soil water had no significant difference between LM and control plots. $NO_3$-N concentration of soil water in LM, however, showed higher concentration (13.6 mg/l at 40 cm, 35.1 mg/l at 80 cm) than control plot (1.5 mg/l at 40 cm, 0.5 mg/l at 80 cm). In case of shallow groundwater quality, pH, heavy metal, etc. were satisfied to the national agricultural water quality standard of groundwater and there were no significant difference between upstream and downstream. The $NO_3$-N concentration of shallow groundwater was also not exceeded the national drinking water standard. However, $NO_3$-N concentration in soil water and downstream of shallow groundwater had increased in 2011 when non-composted LM was applied mostly in non-growing season of tree (September). From the results, it is important to control nitrogen source, application time and decomposed or not when LM is applied. In addition, to investigate nitrate source, further long-term monitoring and modelling could be necessary.

• The Journal of Engineering Geology
• /
• v.25 no.1
• /
• pp.21-33
• /
• 2015

This study tests the potential of detecting small-magnitude earthquakes (~M3.0) and their precursors using a long-term groundwater-monitoring database. In groundwater records from April to June 2012, abnormal changes in water level, temperature, and electrical conductivity were identified in the bedrock monitoring wells of the Gimcheon-Jijwa, Gangjin-Seongjeon, and Gongju-Jeongan stations. These anomalies could be attributed to the M3.1 earthquake that occurred in the Youngdeok area on May 30th, although no linear relationship was found between the scale of changes and the distance between each monitoring station and the epicenter, which is attributed in part to the wide screen design of the monitoring wells. Groundwater monitoring networks designed specifically for monitoring earthquake impacts could provide better information on the safety of underground space and on the security of emergency water-resources in earthquake disaster areas.

• Journal of Soil and Groundwater Environment
• /
• v.12 no.5
• /
• pp.86-97
• /
• 2007

The principal component analysis was performed to identify the general characteristics of groundwater level changes from 202 deep and 112 shallow wells monitoring data, respectively, which came from the National Groundwater Monitoring Stations operated by KWATER with time spans of 156 continuous weeks from 2003 to 2005. Eight principal components, which accounted for 80% of the variability of the original time series, were extracted for water levels of shallow and deep monitoring wells. As a result of cluster analysis using the loading value of three principal components for shallow wells, shallow monitoring wells were divided into 3 groups which were characterized with a response time to rainfall (Group 1: 4.6 days, Group 2: 24.1 days, Group 3: 1.4 days), average long-term trend of water level (Group 1: $2.05{\times}10^{-4}$ m/day, Group 2: $-7.85{\times}10^{-4}$ m/day, Group 3: $-3.51{\times}10^{-5}$ m/day) and water level difference (Group 1 < Group 2 < Group 3). Additionally, they showed significant differences according to a distance to the nearest stream from well (Group 3 < Group 2 < Group 1), topographic slope of well site (Group 3: plain region, Group 1: mountainous region) and groundwater recharge rate (Group 3 < Group 2 < Group 1) with a p-value of 0.05.

• Economic and Environmental Geology
• /
• v.39 no.5 s.180
• /
• pp.537-554
• /
• 2006

Water levels of thermal groundwater ($>30^{\circ}C$) were recorded from March 2002 to June 2006 at several monitoring wells within the Yuseong spa area. Using these data, we elucidated the long-term cyclic fluctuations of thermal groundwater levels with 1 year period. We also observed a noticeable water level variation with periods of 0.5, 1 and 7 days in most monitoring wells, which indicates relatively good hydraulic connectivity within the main hotspring area. By comparing water level variations among several wells, we found out that E-W and N-S trending geological structures should be an important control factor for emplacement and flow of thermal groundwater in the study area. It may be also inferred that geothermal source is highly associated with the hydraulic connectivity of aquifers at the Yuseong spa area.

• Journal of Korea Water Resources Association
• /
• v.32 no.4
• /
• pp.501-510
• /
• 1999

Stream and groundwater qualities of small agricultural watershed in Kangwon Probince, Korea were monitored 1 to 2 years, and the relationships between stream and groundwater qualities and seasonal water quality changes analyzed. Flooded paddy fields influenced groundwater level and quality during rice culture. The differences between groundwater levels during rice culture and non-culture spans were between 0.8 and 2.91 m. Seasonal changes of total nitrogen and nitrate nitrogen concentrations of stream and groundwater were very similar and groundwater quality was thought to have a profound impact on stream quality of the research watersheds. Suspended solids and BOD maintained the first degree stream water quality throughout the monitoring period except for a few and short flooding spans. The concentrations of total phosphorus and total bacteria of both waters showed wide variations and any seasonal trends were not observed. Long-term monitoring studies on small rural watersheds were recommended to understand the pattern of both stream and groundwater quality changes with respect to land use, season and cultural practice, and to apply the results to develop effective water quality management policies for large river and domestic water supply systems.

• The Journal of Engineering Geology
• /
• v.8 no.1
• /
• pp.51-73
• /
• 1998

Hydrogeological systems in a metrnpolitan area can be understood by analyzing the groundwater disturbing factors such as constructions and land applications, the groundwater usage for domestic and industrial purposes, and the groundwater pumpage to lower the groundwater level for the structural safety of subway and underground facilities. This study is part of the study performed to understand the groundwater system in the Seoul area and it is focusing on the hydraulic properties. Groundwater well inventory, barometric efficiency measurements, pumping and slug tests, and long-term groundwater monitoring have been perfonrmed during the last 2 years. The relations between Han River and the groundwater around the river also have been observed. These observations and test data, together with the information on soil distribution, geology, and logging data are used to construct a database and GIS(Geographic Information System) presentation system using ARC/INFO. Barometric efficiencies appeared to have no special trends associated with well depths, which maeans that the degree of confinement of the crystaline rock aquifer of the Seoul area is distributed locally depending on the developrnent of fractures. Hydraulic conductivities exponentialiy decrease with well depth. The stage of Han River fluctuates according to the tidal movement of nearby seawater but the tidal effects attenuate due to the underwater dams. Groundwater levels in the Seoul area seem to have declined for the last two years,but it is not certain that the declination represents the long-term trend.