Yu-Chul Park

Establishing the Origin of Elevated Uranium Concentrations in Groundwater near the Central Ogcheon Metamorphic Belt, Korea.

We examined the origin of the U-enriched groundwater in Daejeon, near the Ogcheon U zone in Korea. For this study, groundwater ionic species and C, S, and Sr isotopic compositions were analyzed. The U-enriched groundwater occurred only in the Daejeon granite region, while all the groundwater in the Ogcheon Supergroup showed very low U concentrations. In the granite region, the pedospheric or atmospheric origin of dissolved C and S means that the aquifer has been well connected to the oxidized surface environment. The Sr/Sr ratios indicated a lithospheric origin of Sr. Groundwater isotopic compositions in the Ogcheon belt varied greatly, indicating their complex sources. In this region, dissolved C originated from graphite-rich slate and limestone. The broad range of δS suggested that the composite sources included atmospheric SO for most groundwater, lithogenic SO for mine drainage and quarry water, and anthropogenic SO for polluted groundwater. This study indicates that the U-enriched groundwater is not related to the present U ores in the Ogcheon belt but is genetically associated with the granite body itself. The varying but considerable U contents within the granite body can be present as isolated groups. We infer that locally high U contents in the Daejeon granite might inherently be due to assimilation of the Ogcheon U-mineralized zone into granitic melt during the Mesozoic; however, the pH and Eh conditions except aquifer geology were very important factors in developing highly enriched U groundwater in the Daejeon granite region. Thermodynamic modeling highlights the importance of dissolved Ca and (bi-)carbonate in U geochemistry.

Effects of the Correlation Length on the Hydraulic Parameters of a Fracture Network

We consider the influences of correlation length and aperture variability on the REV, the equivalent permeability of a fracture network, and the uncertainty in the equivalent permeability using a two-dimensional orthogonal bond percolation model. The percolation threshold, correlation length, effective conductivity, and coefficient of variation of the effective conductivity are investigated over statistically representative multiple realizations with Monte Carlo simulations in 2D fracture networks that have log-normally distributed individual fracture permeabilities. We show that although the aperture variability is large, the REV and the correlation length are similar near the percolation threshold. In contrast, when the fracture density is much larger than the percolation threshold they diverge as the aperture variability increases. We characterize the effects of correlation length and aperture variability on effective conductivity with a simple function. From the coefficient of variation analysis, the correlation length can be a criterion for evaluating which conceptual model is appropriate for describing the flow system for a given fracture network when aperture variability is sufficiently small. However, discrete fracture network models are recommended for flow simulation models because of the difficulty of REV estimation and the uncertainty in equivalent hydraulic parameters when aperture variability is large.

Monitoring of Geothermal Systems Wells and Surrounding Area using Molecular Biological Methods for Microbial Species

This study was conducted to monitor microbial species dynamics within the aquifer due to long term operation of geothermal heat pump system. The species were identified by molecular biological methods of 16S rDNA. Groundwater sample was collected from both open (S region) and closed geothermal recovery system (J region) along with the control. J measured and control as well as S measured found Ralstonia pickettii as dominant species at year 2010. In contrast, Rhodoferax ferrireducens was dominantly observed for the control of S. In 2011, Sediminibacterium sp. was universely identified as the dominant species regardless of the monitoring places and type of sample, i.e., measured or control. The difference in the dynamics between the measured and the control was not critically observed, but annual variation was more strikingly found. It reveals that possible environmental changes (e.g. ORP and DO) due to the operation of geothermal heat recovery system in aquifer could be more exceedingly preceded to differentiate annual variation of microbial species rather than positional differences.

A Study on Hydrochemistry Characteristics of Groundwater and Surface water near a Petroleum Contaminated area

The aim of this study was to examine chemical and isotopic compositions of groundwater and lake water near an area contaminated by petroleum and to evaluate influence of petroleum on them during the period from March to August 2011. In dry season, Ca 2+ and SO4 2� were dominant in the groundwater and lake water and Ca 2+ and HCO3 � were significant in wet season. δ 18 O and δD of the groundwater and lake water were plotted near LMWL (δD = 8.06δ 18 O + 12.5). δ 18 O and δD of the lake water did not show seasonal variation. However, δ 18 O and δD of the groundwater were enriched in wet season compared with those in dry season because of influence of small ponds around wells where evaporation losses were slightly experienced. Redox condition of most lake water was oxidation environment in contact with the atmosphere during the study period. However, redox condition of groundwater was transitional environment in dry season and oxidation environment in wet season because of influence of contaminant such as petroleum. In some groundwater, the concentrations of NO3 � in some groundwater were less than 1 mg/L because of denitrification. Also, NO3 � showed positive correlation with SO4 2� and weak negative correlation with HCO3 � , because of influence of denitrification.

Cost-effective optimal design of a pump-and-treat system for remediating groundwater contaminant at an industrial complex

Trichloroethylene (TCE) and other solvents are found as groundwater contaminants in industrial complexes. Pump-andtreat (PAT) systems are commonly selected for remediation, but have the disadvantages of long operation time and high cost. To reduce the remediation time and cost of PAT systems, a cost-effective optimal design was obtained with a simulation–optimization model. MODFLOW and MT3DMS were used for simulating groundwater flow and contaminant transport. A genetic algorithm was used for optimization, and a parallel computing technique was used for faster optimization. Cost-effective optimal design was achieved using two objective functions, which calculated the total remediation cost by means of installation, operational, and maintenance costs. Based on the restrictions in the study area, two remediation scenarios were examined. Scenario 1 involved the removal of TCE, and Scenario 2 involved the containment of TCE within the compliance line. The total remediation costs of scenario 2 were 77.4~90.4% of scenario 1. The remediation time decreased from 9.87 years in scenario 1 to 8.13 years in scenario 2. Sensitivity analysis determined the effects of installation, operational, and maintenance costs on the total remediation cost, showing that optimal total cost and remediation time were most affected by operational cost. A parallel computing technique using 40 networked slave processes increased optimization speed by 16.9 times. However, the efficiency of the parallel computing technique decreased as networking time increased.

Unexpected nationwide nitrate declines in groundwater of Korea

Elevated levels of nitrate in groundwater are an important concern for health and the environment. The overapplication of nitrogen (N) fertilizer to croplands is one of the major sources of high nitrate content in groundwater. In this study, we analyse the nitrate concentrations in Korean groundwater based on data from groundwater quality monitoring wells (n=1,022–2,072), which were sampled twice annually over a recent 13-year analysis period (2001–2013). We report that groundwater nitrate levels are decreasing, despite steadily increasing groundwater use. The maximum nitrate concentration decreased from 168.91 to 48.11 mg/L, while the mean values also show a gradual decreasing trend. Nonparametric Mann-Kendall tests on nitrate concentrations also confirm the decreasing trend. The nitrate decrease is more clearly evident in agricultural groundwater as compared to domestic and drinking groundwaters. This decrease of nitrate in groundwater coincides with a large decline in N fertilizer application due to reduced cropland areas, more sustainable agricultural practices, and progressive improvement of sewage disposal services. This study proposes that the long-term adoption of best practices in agriculture has had a positive impact on groundwater nitrate control.