• Economic and Environmental Geology
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• v.36 no.5
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• pp.339-347
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• 2003

Using 171 groundwater chemistry data, seawater intrusion in the Ulsan area was studied. The area near the downstream area of the Taehwa River shows the higher Cl concentrations(11,300 mg/L in maximum), whereas the Cl concentrations are generally low in the eastern coastal area maybe due to the geology of the area. When Cl concentrations are very low, groundwater shows Br:Cl weight ratios significantly deviating from the Br:Cl ratio of seawater($34.7{\times}10^{-4}$). However, Br:Cl ratios are very close to the value of seawater when Cl concentrations are higher than 100 mg/L. Eleven groundwater samples having very high Cl concentrations(>500 mg/L) show that ionic ratios for Ca, Mg, $SO_4$, $HCO_3$ and $SiO_2$ are considerably different from those of seawater. This indicates that the origin of the high Cl groundwaters occurring along the Taehwa River are likely to be the residual salines from the salterns previously located on the alluviums rather than the seawaters intruded recently. These waters seem to be accumulated in the sediments before the drastic expansion of the city. Considering the characteristics of the urban groundwater system where the inflow exceeds the outflow, it is anticipated that the high Cl concentration in the groundwater show a decreasing trend in the future.

• Journal of Environmental Science International
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• v.7 no.4
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• pp.461-466
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• 1998

One hundred and thirty two ground water samples from the Usan area were divided into urban and non-urban groupings and were assessed between 1993 and 1996. The results of statistical analysis were as follows: There were significant differences between the two groupings in the average value of the following water quality parameters: total hardness, nitrate , pH, iron, ammonia and chloride ion in the order of Z-score . Because total hardness, nitrate, and pH were also significant in ANOVA test, these three parameters can be regarded as the most sensitive parameters of artirial pollutants. By the comprehensive com- parison of Ulsan water Quality to that of Kangwon-do, all of the major parameters(pH, KMnO4 consumption, sulfate, chloride and hardness except nitrated were confirmed as being significantly Increased levels.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1925-1928
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• 2007

Water cycle analysis was performed for Gunja basin located in metropolitan Seoul using Aquacycle model in order to assess the problems of urban water cycle. From the water cycle analysis of Gunja basin, it was found that 75% of total rainfall occurred in the form of surface runoff, and groundwater recharge only accounted for about 7%. This suggests serious distortion of water cycle which can be attributed to urbanization. Feasibility analysis of reuse scenarios such as rainwater use and wastewater reuse was then performed to examine their influences on improving the water cycle. From the analysis of water reuse options, it was shown that imported water supply savings of 13% can be achieved through rainwater use, and water supply savings of 31% through wastewater reuse.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.29-30
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• 2018

Recent impervious pavements on roads and sidewalks cause rainwater to not penetrate into the ground, deplete groundwater, or flood the rivers, causing urban flood damage. In order to solve these problems, the amount of installed pitcher block is increasing, but the existing pitcher block is made with cement base and causes many problems. In the cement permeable block, the efflorescene phenomenon occurs due to the acid component, and the pore of the permeable block is clogged and the permeability is lost. As a result, the service life of the pitcher block is shortened and the replacement period is shortened. The purpose of this study is to analyze the basic properties of polymer concrete by replacing cement with polymer in order to solve the problem of cement - based concrete permeable block.

• Environmental Engineering Research
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• v.21 no.2
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• pp.211-218
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• 2016

Cheonggye-cheon is a partly restored urban stream located in central Seoul. We monitored fecal contamination using three different fecal indicators, total coliforms (TC), fecal coliforms (FC) and E. coli, to assess differences in each indicator on days of varying weather conditions. Presumptive TC, FC and E. coli colonies were identified by their 16S rRNA sequences. The results showed that enumeration of E. coli provided a better reflection of fecal contamination of the stream than TC and FC. The main sources of contamination were the inflow of fecal-polluted groundwater from the vicinity of a subway line and two inflowing streams. The fecal contamination was worsened on days with heavy rain because untreated sewage from a collecting facility flowed into the stream. Moreover, growth potential of fecal indicator (E. coli) in situ induced by algal exudates was measured. Our results suggest that an appropriate standard based on E. coli rather than TC and FC should be established for improving water quality management strategies of Cheonggye-cheon in the future.

• Ecology and Resilient Infrastructure
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• v.3 no.2
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• pp.126-129
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• 2016

The risk of flooding and groundwater depletion is increasing due to the increase of impervious area in an urban area that reduces the volume of infiltration and increases the outflow of rainwater. The objective of this study is to examine the impact of installation of roadside tree protectors with infiltration pipes in terms of the change of the infiltration rate. Through this study, it has been attested that roadside tree protectors with infiltration pipes increased the infiltration rate and decreased water level on the ground, and could be applied in an urban area as the low impact development (LID) facilities.

• Geomechanics and Engineering
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• v.28 no.6
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• pp.573-584
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• 2022

Water inrush may occur during seaside urban tunnel excavation. Various factors affect the water inrush, and the water inrush mechanism is complex. In this study, nine evaluation indices having potential effects on water inrush were analysed. Specifically, the geographic and geomorphic conditions, unfavourable geology, distance from the tunnel to sea, strength of the surrounding rock, groundwater level, tidal action, cyclical footage, grouting pressure, and grouting reinforced region were analysed. Furthermore, a two-step interval risk assessment method for water inrush management during seaside urban tunnel excavation was developed by a multi-index system and interval risk assessment comprised of an interval analytic hierarchy process, fuzzy comprehensive evaluation, and relative superiority analysis. The novel assessment method was applied to the Haicang Tunnel successfully. A preliminary interval risk assessment method for water inrush was performed based on engineering geological conditions. As a result, the risk level fell into a risk level IV, which represents a section with high risk. Subsequently, a secondary interval risk assessment method was performed based on engineering geological conditions and construction conditions. The risk level of water inrush is reduced to a risk level II. The results agreed with the current tunnel situation, which verified the reliability of this approach.

• Geomechanics and Engineering
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• v.35 no.2
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• pp.109-119
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• 2023

Ground subsidence in urban areas due to excessive development and degraded underground facilities is a serious problem. Geophysical surveys have been conducted to estimate the distribution and scale of cavities and subsidence. In this study, electrical resistivity tomography (ERT) was performed near an area of road subsidence in an urban area. The subsidence arose due to groundwater leakage that carried soil into a neighboring excavation site. The ERT survey line was located between the main subsidence area and an excavation site. Because ERT data are affected by rapid topographic changes and surrounding structures, the influence of the excavation site on the data was analyzed through field-scale numerical modeling. The effect of an excavation should be considered when interpreting ERT data because it can lead to wrong anomalous results. A method for performing 2D inversion after correcting resistivity data for the effect of the excavation site was proposed. This method was initially tested using a field-scale numerical model that included the excavation site and subsurface anomaly, which was a loosened zone, and was then applied to field data. In addition, ERT data were interpreted using an existing in-house 3D algorithm, which considered the effect of excavation sites. The inversion results demonstrated that conductive anomalies in the loosened zone were greater compared to the inversion that did not consider the effects of excavation.

• Journal of Soil and Groundwater Environment
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• v.24 no.6
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• pp.9-15
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• 2019

Soil dust emitted from large scale construction sites in urban areas has posed a significant health threats to local residents by exacerbating air quality. Water-spraying (moistening) is commonly practiced to lower the dust emission in construction sites, but its long term effectiveness is highly questionable. In this study, the utility of starch and PVA(polyvinyl alcohol) was investigated in suppression of the soil dust emissions in construction sites in Seoul areas. The efficiency of the two suppressants was tested with test soil sample in a lab-scale wind tunnel box under different concentrations of suppressants and soil textures. Starch and PVA showed the superior ability to suppress soil dust emission as compared to moistening, resulting in PM₁₀ and PM_2.5 lower than the daily limit values of 30 and 15 ㎍/㎥ respectively. PVA showed higher suppression capability than starch for all conditions. The test soils mixed with suppressants also showed dramatically enhanced aggregate stability compared to the non-treated soil.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.259-267
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• 2007

An efficient algorithm for inverting static-shifted magnetotelluric (MT) data has been proposed to produce a three-dimensional (3D) resistivity model. In the Gauss-Newton approach, computational costs associated with construction of a full sensitivity matrix usually make 3D MT inversion impractical. This computational difficulty may be overcome by using approximate sensitivities. We use four kinds of sensitivities in particular orders in the inversion process. These sensitivities are computed 1) analytically for an initial, homogeneous earth, 2) exactly for a current model, 3) approximately by the Broyden method, and 4) approximately using the previous adjoint fields. Inversion experiments with static-shifted synthetic and field MT data indicate that inversion results are highly dependent on characteristics of data and thus applying various combinations of sensitivities is helpful in obtaining a good image of the subsurface structure with reasonable computation time.