Assessment of groundwater chemistry in a coastal region (Kunsan, Korea) having complex contaminant sources: a stoichiometric approach

Groundwater chemistry in a coastal region (Kunsan, Korea) having complex contaminant sources was investigated. Water analysis data for 197 groundwater samples collected from the uniformly distributed sixty-six wells were used. Chemical analysis results indicate that groundwaters show wide concentration ranges in major inorganic ions, reflecting complex hydrochemical processes. Due to the complexity of groundwater chemistry, the samples were classified into four groups based on Cl and NO₃ concentrations and the processes controlling water chemistry were evaluated based on the reaction stoichiometry. The results explained the importance of mineral weathering, anthropogenic activities (nitrification and oxidation of organic matters), and Cl-salt inputs (seawater, deicer, NaCl, etc.) on groundwater chemistry. It was revealed that mineral dissolution is the major process controlling the water chemistry of the low Cl and NO₃ group (Group 1). Groundwaters high in NO₃ (Groups 2 and 4) are acidic in nature, and their chemistry is largely influenced by nitrification, oxidation of organic matters and mineral dissolution. In the case of chloride rich waters (Group 3), groundwater chemistry is highly influenced by mineral weathering and seawater intrusion associated with cation-exchange reactions.     

Untersuchungen zur Abtrennung von Schwermetallen aus Abwasser mit frisch hergestelltem Magnetit Studies for Separation of Heavy Metals from Wastewater with Freshly Precipitated Magnetite

The separation of heavy metals from wastewater may be improved by precipitation/flocculation with iron- or aluminium salts. Often, the resulting products are voluminous, water-containing, amorphous hydroxides which show only limited flocculation properties and may possibly pose problems with the technical separation from the aqueous phase. The application of magnetite could be advantageous because magnetite is ferromagnetic and can be separated very quickly in a magnetic field. First of all, a simple preparation method for magnetite was studied. Pure magnetite could be prepared by mixing an iron(II) salt solution with an equivalent amount of sodium hydroxide at room temperature without oxidation by air. The required reaction time was only 3 hours. For the precipitation of heavy metals from an electroplating wastewater, a better metal elimination and smaller sludge volumes resulted with that artificially produced magnetite in comparison with a precipitation by NaOH. Thereby not only the adsorption of metals was established but also coagulation effects of the magnetite sludge with small metal hydroxide particles. By means of the experimental results. sorption of nickel and chromium was compiled as function of pH and precipitation time. Because freshly precipitated magnetite shows very good sorption and flocculation properties, and pH of precipitation may be lower, its use in high gradient magnetic separation (HGMS) could be more effective for metal elimination than magnetite powder.     

Strontium isotopic equilibration during metamorphism of tillites from the Ogcheon Belt,South Korea

The NE/SW trending Ogcheon Belt formed during the Mesozoic by deformation and metamorphism of a sedimentary sequence which includes tillite formations of late Precambrian or Lower Palaeozoic age. In this study Rb-Sr isotopic data are reported from cm-scale sampling of clasts and matrix in these tillites, which underwent metamorphism at grades ranging from the biotite zone to the kyanite zone. Sr-isotopic disequilibrium between clasts and matrix persists up to the highest grade but in four out of five rocks the matrix samples approximate to isochrons (MSWD's<12). The mechanism for this selective isotopic equilibration is considered to be related to the metamorphic reactions in the matrix, which were probably accompanied by a substantial fluid flow. The matrix isochrons for three of the rocks, together with separated white micas from associated schists, suggest that metamorphism took place in the Trias, approximately 200 Myr ago. Metamorphism was followed by slow cooling and biotite closure temperatures were not reached until 190-150 Myr. — These results suggest that where high fluid/rock ratios can be demonstrated on independent petrological grounds, the analysis of small-scale whole-rock samples may allow effective Rb/Sr dating of metamorphism.     

Thermo-mechanical Stability Analysis for a Multi-level Radioactive Waste Disposal Concept

To dispose of the spent fuels generated from the Korean nuclear power plants in an underground repository, a large area of about 4 km² is required. This could be a constraint for selecting an adequate repository site and it is required to investigate the possibility of a multi-level repository design. In this study different parameters related to the multi-level repository design such as the level distance, waste type disposed of at each level, and the time interval between the operations at the levels, were investigated using the three-dimensional code, FLAC3D. For obtaining more reliable results, rock properties measured from deep boreholes were used. From the analysis, it was possible to conclude that a multi-level repository concept could be an attractive alternative to reduce the underground area as well as to dispose of the spent fuels from Pressurized Water Reactors (PWR) and Canadian Deuterium Uranium (CANDU) reactors at different levels with different time schedules.     

Sequential tracer tests for determining water seepage paths in a large rockfill dam, Nakdong River basin, Korea

The rockfill dam of this study has a clay core, filter zone, and sandy gravel shell, and it is located in the Nakdong River basin in Korea. Filling the reservoir began in August 1994 and it was full by April 1998. When the reservoir level was approximately 150 m, three settlement holes were found in the dam crest. To determine possible seepage paths and potential damaged areas within the rockfill dam, 15 tracer tests were performed during two periods. During the two test periods, six and nine tracer tests were conducted when the average water levels of the reservoir were 145 m and 142 m, respectively. Rhodamine WT (RWT) and bromide ion were used as tracers. For each test, 1800 to 4000 L of tracer solution were injected into the riprap for about 5 h. The 15 injection points were uniformly distributed from the right to left sides of the embankment and the two tracers were injected alternately. Tracer concentrations were monitored at 26 observation wells, which were divided into four groups by their geographical positions: right side of the crest, left side of the crest, right side of the dam toe, and left side of the dam toe. For each tracer test, more than 30 water samples were taken during a period of 96 h at each observation well. Based the breakthrough curves obtained from the sequential tracer tests, it was inferred that the most probable seepage paths and potential damaged area were in the left side of the crest (tongue wing zone) and, to a lesser extent, in the right side of the dam abutment.     

Capturing the heterogeneity of urban growth in South Korea using a latent class regression model

This study aims to analyze the spatial patterns of urban growth in South Korea between 2000 and 2010. Fourteen suspected causative independent variables were selected and latent class regression (LCR) was used to analyze the relationship between dependent (urban growth) and independent (causative) variables. The goodness‐of‐fit was assessed by comparison to logistic regression (LR) analysis. The LR analysis produced consistent coefficients for each independent variable across the study area. In contrast, an LCR analysis, with a three‐class assumption, resulted in a different magnitude and directional effects of the coefficients for each class. The LCR analysis enabled the identification of both spatially homogeneous and heterogeneous areas. In addition, the LCR analysis performed better than the LR analysis with a lower Akaike information criterion and Bayesian information criterion value, and a higher receiver operating characteristic value. We conclude that LCR analysis should be used to establish causative “driving” factors for efficient urban growth planning and urban spatial policy.     

Predicting future urban impervious surface distribution using cellular automata and regression analysis

Urban impervious surfaces are considered as key indicator of urbanization intensity and environmental quality. Due to their significant impact on surface runoff, flood frequency, and water quality, impervious surfaces have been identified as an important indicator for examining the hydrological impact of urbanization. The amount and distribution of impervious surfaces have been estimated using remote sensing and geographic information system (GIS) techniques. Little research, however, has been conducted to predict future impervious surface distributions. To address this problem, we developed an integrated residential/commercial growth and impervious surface distribution model to predict urban impervious surface distribution. Taking Milwaukee River Basin, Wisconsin as a case study, we simulated future residential and commercial developments using a CA model. Further, we developed a linear regression model to predict impervious surface distributions in residential and commercial land uses. Analysis of results suggests that the proposed model performs significantly better than the traditional approaches.