Ho-Wan Chang

The resolution of stratigraphic inconsistency in the luminescence ages of marine terrace sediments from Korea

Several sets of marine terraces are exposed along the southeastern coast of the Korean peninsula. The formation ages of these terraces have attracted considerable attention because they provide essential information on local crustal stability. Over the last few years considerable effort has been put into the determination of these ages using optically stimulated luminescence (OSL) dating of the marine sediments from which the terraces were built. For several sites, the results of dose recovery tests and other OSL characteristics, including the dependence of equivalent dose on heat treatment prior to stimulation, have been described in detail elsewhere (Quat. Sci. Rev. 22 (2003) 407). However, it has been found that the samples from one site exhibit various undesirable OSL characteristics, which result in stratigraphically inconsistent OSL ages. In this paper, we investigate these characteristics, and use luminescence component separation to resolve this inconsistency. The resolved OSL ages obtained as such are then used for the discussion on the local crustal stability of the southeastern coast of Korea during the Late Pleistocene.

Hydrogeochemical characteristics of groundwater in a mid-western coastal aquifer system, Korea

Hydrogeochemical characteristics of shallow groundwater in a mid-western coastal aquifer system, Korea have been investigated to identify the salinization process. The spatial distributions of the groundwater components are well consistent with the groundwater flow pattern that follows topography in the study area. The groundwater at many locations in the study area is not suitable for drinking water because of its high salinity, which is mainly caused by seawater intrusion. The chemical composition of the groundwater is characterized by high chloride concentration and high variations in cation concentrations due to the cation exchange reaction between aquifer minerals and seawater components. The similar distributions of chemical components between rainy and dry seasons suggest that the groundwater flow system is almost in a steady state condition. The groundwater is classified into Ca(HCO3)2, CaCl2, and NaCl types based on its hydrogeochemical characteristics. The groundwater from the alluvial aquifer shows higher salinity in the rainy season than the dry season while the groundwater in the bedrock aquifer shows lower salinity year-round. Isotope data and factor analysis also indicate that the hydrogeochemical characteristics of groundwater are not only influenced by seawater intrusion but also by agricultural activities.

Groundwater flow system inferred from hydraulic stresses and heads at an underground LPG storage cavern site

Underground Liquefied Petroleum Gas (LPG) storage caverns were constructed below the groundwater table to contain pressurized gas by groundwater pressure. Continuous and regular groundwater monitoring data were used to analyze whether the gas containment condition was satisfied or not. The monitoring data included time series analysis of hydraulic heads, gas and groundwater pressures, and groundwater chemistry. Through cross-correlation analyses of the time series data, the major factors causing hydraulic head fluctuation were found to be groundwater recharge from precipitation and cavern gas pressures. Hydraulic head and hydrochemical data indicate that a fault zone acts as the groundwater recharge zone and water curtain tunnels reduce head fluctuations.

Application of cluster analysis for the hydrogeochemical factors of saline groundwater in Kimje, Korea

The main hydrogeochemical characteristics of shallow groundwater in the coastal area at Kimje city, Korea, have been identified in the present study. From cluster analysis, the groundwater in the study area is classified into four groups (A, B, C, and D). Groundwaters in B, C, and D groups are strongly affected by the present seawater and the trapped old seawater because the area including B, C, and D groups contacts the Yellow Sea and contains the reclaimed land. They also are governed by reduction processes. On the other hand, groundwater in group A has been largely affected by chemical fertilizers because its land has been used for the agricultural activities for a long time. As groundwater flows from group A to group D according to its path, the governing factor of the groundwater quality gradually tends to change from chemical fertilizers into reduction processes and seawater intrusion.

Effect of Tween surfactant components for remediation of toluene-contaminated groundwater

The objectives of this study were to select potentially suitable surfactants that solubilize toluene present as a contaminant and to determine the effectiveness of toluene removal from groundwater by the selected surfactants. Four different surfactants of Tween series were chosen based on surfactant types, toxicity, HLB (Hydrophilic-Lipophilic Balance), CMC (Critical Micelle Concentration). In the separatory funnel experiments, Tween 20 was not able to solubilize at least 1 mL of toluene and was considered ineffective. Tween 40, Tween 60 and Tween 80 were relatively good toluene solubilizers. The highest recovery (98%) of the toluene was obtained using a nonionic surfactant (Tween 60) in the batch experiments. In Tween series surfactant, the trend of ionic strength magnitude in sampled groundwater was closely related with that of recovery rates. The ionic strength of aqueous phase had a strong effect in aqueous activity. The aqueous activity was decrease when ionic strength was increased. The test methods employed may be useful for rapid selection of surfactants and are essential for reducing cost in surfactant-assisted remediation. Also, these selected surfactants are expected to be in practical use for remediation of toluene-contaminated groundwater.

Synergism effect of mixed surfactant solutions in remediation of soil contaminated with PCE

The purpose of this research was to evaluate the effect of mixed surfactant solution for removal of perchlorethylene (PCE) in sandy soil. Ten different surfactant solutions were used in column studies. Mixed surfactant solutions (anionic and nonionic) were most effectively worked in the sandy soil for removal of PCE as a result of synergism between the two types of surfactants. The effectiveness of the mixture of surfactants [anionic DOSL (Diphenyl Oxide Disulfonates) and nonionic Tween 60] was 35–38% greater than that for the anionic or nonionic surfactant alone. However, synergism between the anionic SDS (Sodium N-dodecyl Sulfate) and the anionic DOSL was not observed. Cause of the lack of synergism in a mixture of the two anionic surfactants is uncertain but may result from the twin head structure of DOSL. The results indicate that mixed surfactant solution (1∶1 mixture of anionic and nonionic) leaching is a promising candidate for the remediation of PCE contaminated sandy soil.

Hydrochemistry and isotope geochemistry of Song Stream, a headwater tributary of the South Han River, South Korea

To investigate the geochemical and isotopic characteristics of a headwater tributary of the South Han River, we analyzed major elements, stable isotopes of oxygen, hydrogen, carbon, and sulfur, and strontium (Sr) isotopes of stream and groundwater samples collected from the Song Stream watershed in summer 2003. The stream water samples of the study area were divided into three water types, among which dissolved ion concentrations differed considerably. Our results strongly indicate that the chemical composition of Song Stream is controlled by silicate and carbonate weathering, as well as anthropogenic contamination, and variations in major dissolved ions and Sr isotopic ratios are mainly correlated to lithological variations in the watershed. The dissolved loads of the main channel of Song Stream are largely controlled by carbonate dissolution. Thus, the water chemistry of the main channel is probably dominated by the chemical weathering of carbonates, even where carbonates comprise only a minor proportion of the bedrock geology. The Sr isotopes and Mg/Ca molar ratios indicate that a dolomite end-member may exist in the study area, which would be compatible with the cationic characteristics of Song Stream. All groundwater samples from the study area, except for one, had significantly high nitrate concentrations (0.75–2.42 mmol/L) that exceeded the drinking-water standard and possibly resulted from both sewage and agricultural inputs.