Tracing of residual multiple DNAPL sources in the subsurface using 222Rn as a natural tracer at an industrial complex in Wonju, Korea

Depth-discrete tracing of residual dense non-aqueous phase liquid (DNAPL) sources in the subsurface is of great importance in making decisions related to contaminated groundwater remediation. Temporal variations in the natural tracer ²²²Rn and contaminant concentrations in groundwater contaminated with multiple chlorinated contaminants, such as trichloroethene, carbon tetrachloride, and chloroform, were examined to trace residual multiple DNAPL contaminants at an industrial complex in Wonju, Korea. The ²²²Rn activities and multiple DNAPL concentrations in the groundwater fluctuated irregularly according to the groundwater recharge. The natural tracer ²²²Rn in groundwater present in the soil layer, originating from the underlying crystalline biotite granite, had a wide range from 29,000 to 179,000 Bq/m³, and total concentrations of chlorinated solvents ranged from 0.06 to 17.77 mg/l, indicating the ambiguous results of ²²²Rn for tracing the residual DNAPL sources. In this paper, a method is presented to locate zones with a high probability of containing depth-discrete residual multiple DNAPL sources using ²²²Rn and considering relative contaminant concentrations. The results demonstrate that the combination of the ²²²Rn activities as a natural tracer and the relative contaminant concentrations is able to be used as a useful tool for tracing residual DNAPLs.     

Phytoremediation by benthic microalgae (BMA) and light emitting diode (LED) in eutrophic coastal sediments

Ocean Science Journal - In this study, we examined whether phytoremediation using benthic microalgae (BMA) and a light emitting diode (LED) can remediate eutrophic sediments caused by promoting the...     

A review of the National Groundwater Monitoring Network in Korea

The drastic expansion of cities and the rapid economic growth in Korea have caused dramatic increases to demand from groundwater supplies for drinking, domestic, agricultural and industrial water usage. The Ministry of Construction and Transportation and the Korea Water Resources Corporation have constructed and operated the National Groundwater Monitoring Network (NGMN) throughout the country since 1995. The NGMN, an official project establishing a total of 320 groundwater monitoring stations, was completed in 2005. Each national groundwater monitoring station serves as a baseline and primary station to monitor long‐term general trends in water‐level fluctuations and in groundwater quality. The present NGMN and its monitoring capabilities were evaluated to enhance the efficiency of groundwater monitoring and to meet the new societal conditions. Based on reviews and evaluations, some suggestions and recommendations are made with regard to improvements of the national network, including the installation of rainfall gauges in groundwater monitoring stations, gathering groundwater data every hour instead of every 6 h as at present, involving major cations and anions in the regular and periodic chemical analyses, regular periodic analyses of collected groundwater data, and construction of 199 additional groundwater monitoring stations to supplement the existing groundwater monitoring network. Copyright © 2006 John Wiley & Sons, Ltd.     

Long-Term Consolidation and Strength Behavior of Marine Clay Improved with Fly Ash

This paper presents an investigation of the long-term consolidation and strength behavior with fly ash as an additive in improving soft marine clay in Wando, Korea. 0%, 5%, 10%, 20% and 25% of the soil was replaced with fly ash. Consolidation tests were performed as incremental loaded tests. In addition, unconfined compressive strength were determined after 1, 14, 28 and 90 days. A series of forty-two long-term consolidation tests that lasted for 60 days under the constant loading were also conducted. Creep settlements of the blends decreased significantly with an increase in fly ash content. The shear strength properties increased with an increase in fly ash content. Statistical evaluation reveals an excellent correlation between the measured and predicted undrained shear strengths.     

Influence of Pressure Change During Hydraulic Tests on Fracture Aperture

In a series of field experiments, we evaluate the influence of a small water pressure change on fracture aperture during a hydraulic test. An experimental borehole is instrumented at the Korea Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT). The target fracture for testing was found from the analyses of borehole logging and hydraulic tests. A double packer system was developed and installed in the test borehole to directly observe the aperture change due to water pressure change. Using this packer system, both aperture and flow rate are directly observed under various water pressures. Results indicate a slight change in fracture hydraulic head leads to an observable change in aperture. This suggests that aperture change should be considered when analyzing hydraulic test data from a sparsely fractured rock aquifer.     

Sensitivity analysis of influencing parameters on slit-type barrier performance against debris flow using 3D-based numerical approach

Extreme rainfall-induced debris flow can be catastrophic to an urban area,and installation of slit-type barriers can prevent such damage while minimizing negative impact on environments.However,the performance of slit-type barriers against debris flows remains poorly identified partly due to the innate complexity in interactions between debris flow and solid structure.This paper investigated the flow behaviors of debris affected by slit-type barriers using the computational fluid dynamics(CFD)method,in which the numerical model based on the volume of fluid method was verified using the physical modeling results.The sensitivity analysis was performed by building metamodels to determine the primary parameters influencing the barrier performance against debris flows among various variables,in which the effect of input properties and design parameters,particularly the soil concentration in fluidized debris,initial velocity and volume of debris,the barrier height,and the opening ratio,was evaluated from the perspectives of the flow energy reduction and debris trapping.The initial velocity and volume of debris were found to play a significant role in determining the debris flow characteristics.A decrease in the opening ratio in the channel primarily facilitated the energy reduction and trapping due to the reduced opening size.However,the barrier height exhibited a limited effect when the height was sufficiently high to block the debris flow volume.In addition,it was observed that the double barrier system effectively increased the energy reduction while keeping the benefit of open-type barrier.The developed simulation method and obtained results provide an effective tool and an insight that can contribute to an optimum design of the debris-flow barrier.     

Correlation of geologic logs with spectral methods

Spectral studies of geologic logs demonstrate that automatic well—log correlation can be processed more efficiently in the frequency domain. Cross correlation of the power spectra of well logs identifies the direction and degree of thickening of stratigraphic sequences between two wells. Given the stretch, the displacement between logs is computed by correlation processes without relying on iterative procedures. Beginning with digitized log data of unequal lengths, power spectra are computed. The stretch factor between the two logs is observed as a difference in frequency scaling. A transform to logarithmic frequencies converts the spectra to a form that reduces the scaling effect of the frequencies to a simple displacement between the plots. A Lagrange interpolation procedure permits cross correlation of the two spectra with a variable window size. The peak value of the resultant correlation function identifies the displacement between the spectra and this, in turn, permits calculation of the stretch factor.     

Improvement of overtopping risk evaluations using probabilistic concepts for existing dams

Hydrologic risk analysis for dam safety relies on a series of probabilistic analyses of rainfall-runoff and flow routing models, and their associated inputs. This is a complex problem in that the probability distributions of multiple independent and derived random variables need to be estimated in order to evaluate the probability of dam overtopping. Typically, parametric density estimation methods have been applied in this setting, and the exhaustive Monte Carlo simulation (MCS) of models is used to derive some of the distributions. Often, the distributions used to model some of the random variables are inappropriate relative to the expected behaviour of these variables, and as a result, simulations of the system can lead to unrealistic values of extreme rainfall or water surface levels and hence of the probability of dam overtopping. In this paper, three major innovations are introduced to address this situation. The first is the use of nonparametric probability density estimation methods for selected variables, the second is the use of Latin Hypercube sampling to improve the efficiency of MCS driven by the multiple random variables, and the third is the use of Bootstrap resampling to determine initial water surface level. An application to the Soyang Dam in South Korea illustrates how the traditional parametric approach can lead to potentially unrealistic estimates of dam safety, while the proposed approach provides rather reasonable estimates and an assessment of their sensitivity to key parameters.     

Influence of copper mine on surface water quality

Aras water basin is located in northwest of Iran. Sungun mine which is the largest open-cast copper mine of Iran is located in this region and is in the primary stages of extraction. The influence of mining activity on the quality of regional surface water has been taken in to consideration in this study. Accordingly, sampling was done from 5 local streams in the study area. In order to consider the effect of flow quantity on the amount of different parameters, sampling was done in July and November 2005 when the local streams had the minimum and maximum flow rate respectively. The concentrations of major anions and cations as well as As, Mo, Al, Cu, Cd, Cr, Fe, Mn and Zn were determined. The results showed that the concentrations of metallic ions like aluminum, chromium, copper, manganese, molybdenum and iron in samples collected in July are above USEPA (Environmental Protection Agency) limits; however, mentioned concentrations are lessened remarkably in the samples collected in November. This fact is justified considering dilution of ions concentration via more amount of water in November. The chemical characteristics of water compositions on the basis of major ion concentrations were evaluated on a Schoeller and Piper diagram. Accordingly, the dominant type of water in July and November is considered to be Ca-HCO₃ (calcium-bicarbonate type). Regarding Schoeller diagram, despite relatively high concentration of calcium, the current status of local surface water is acceptable for drinking purposes. By commencing mining excavation with designed capacity in near future, the minerals will come in to contact with air and water resulting in dissolution, especially in ponds, which, in turn, increases the concentration of heavy metals in surface water. Considering consequent uses of this water including drinking, irrigation, industrial, etc. precautions must be taken in to consideration.