• Journal of Soil and Groundwater Environment
• /
• v.21 no.6
• /
• pp.101-113
• /
• 2016

To properly manage and remediate groundwater contaminated with chlorinated hydrocarbons such as trichloroethylene (TCE), it is necessary to assess natural attenuation processes of contaminants in the aquifer along with investigation of contamination history and aquifer characterization. This study evaluated natural attenuation processes of TCE at an industrial site in Korea by delineating hydrogeochemical characteristics along the flow path of contaminated groundwater, by calculating reaction rate constants for TCE and its degradation products, and by using geochemical and reactive transport modeling. The monitoring data showed that TCE tended to be transformed to cis-1,2-dichloroethene (cis-1,2-DCE) and further to vinyl chloride (VC) via microbial reductive dechlorination, although the degree was not too significant. According to our modeling results, the temporal and spatial distribution of the TCE plume suggested the dominant role of biodegradation in attenuation processes. This study can provide a useful method for assessing natural attenuation processes in the aquifer contaminated with chlorinated hydrocarbons and can be applied to other sites with similar hydrological, microbiological, and geochemical settings.

• Proceedings of the KSEEG Conference
• /
• 2002.06a
• /
• pp.81-100
• /
• 2002

While most of regulatory communities in abroad recognize ' 'natural attenuation " to include degradation, dispersion, dilution, sorption (including precipitation and transformation), and volatilization as governing Processes, regulators prefer "degradation" because this mechanism destroys the contaminant of concern. Unfortunately, true degradation only applies to organic contaminants and short- lived radionuclides, and leaves most metals and long-lived radionuclides. The natural attenuation Processes may reduce the potential risk Posed by site contaminants in three ways: (i)contaminants could be converted to a less toxic form througy destructive processes such as biodegradation or abiotic transformations; (ii) potential exposure levels may be reduced by lowering concentrations (dilution and dispersion); and (iii) contaminant mobility and bioavailability may be reduced by sorption to geomedia. In this review, authors will focus will focul on "sorption" among the natural attenuation processes of hazardous inorganic contaminants including radionuclides. Note though that sorption and transformation processes of inorganic contaminants in the natural setting could be influenced by biotic activities but our discussion would limit only to geochemical reactions involved in the natural attenuation. All of the geochemical reactions have been studied in-depth by numerous researchers for many years to understand "retardation" process of contaminants in the geomedia. The most common approach for estimating retardation is the determination of distrubution coefficiendts ($K_{d}$) of contaminants using parametric or mechanistic models. As typocally used in fate and contaminant transport calculations such as predictive models of the natural attenuation, the $K_{d}$ is defined as the ratio of the contaminant concentration in the surrounding aqueous solution when the system is at equilibrium. Unfortunately, generic or default $K_{d}$ values can result in significant error when used to predict contaminant migration rate and to select a site remediation alternative. Thus, to input the best $K_{d}$ value in the contaminant transport model, it is essential that important geochemical processes affecting the transport should be identified and understood. Precipitation/dissolution and adsorption/desorption are considered the most important geochemical processes affecting the interaction of inorganic and radionuclide contaminants with geomedia at the near and far field, respectively. Most of contaminants to be discussed in this presentation are relatively immobile, i.e., have very high $K_{d}$ values under natural geochemical environments. Unfortunately, the obvious containment in a source area may not be good enough to qualify as monitored natural attenuation site unless owner demonstrate the efficacy if institutional controls that were put in place to protect potential receptors. In this view, natural attenuation as a remedial alternative for some of sites contaminated by hazardous-inorganic components is regulatory and public acceptance issues rather than scientific issue.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2005.10a
• /
• pp.182-182
• /
• 2005

• Microbiology and Biotechnology Letters
• /
• v.39 no.1
• /
• pp.86-92
• /
• 2011

Three bioremediation methods, natural attenuation (NA), biostimulation (BS) and bioaugmentation (BA) were applied to remediate diesel-contaminated soil, with their remediation efficiencies and soil microbial activities compared both with and without surfactant (Tween 80). BA treatment employing Rhodococcus sp. EH831 was the most effective for the remediation of diesel-contaminated soil at initial remediation stage. On the addition of surfactant, no significant effect on the remediation performance was observed. A negative correlation was found between the dehydrogenase activity (DHA) and residual concentration of total petroleum hydrocarbons (TPHs) at below 20,000 mg-$TPHs{\cdot}kg$-dry $soil^{-1}$, as follows: DHA (${\mu}g$-TPF(Triphenylformazan)${\cdot}g$-dry $soil^{-1}\;d^{-1}$) = -0.02 ${\times}$ TPHs concentration (mg-$TPHs{\cdot}kg$-dry $soil^{-1}$) + 425.76 (2500 ${\leq}$ TPHs concentration ${\leq}$ 20000, p < 0.01).

• Proceedings of the KSRS Conference
• /
• 1998.09a
• /
• pp.89-94
• /
• 1998

Seasonal variation of attenuation coefficient spectra in Japan sea was extracted from underwater radiance/irradiance spectra observed by a moored buoy system developed by National Space Development Agency of Japan (NASDA). The buoy was deployed 9 months from August 31, 1996 to June 1, 1997. Throughout this period, it was collecting downward irradiance and upward radiance spectra under water at the depth of 1.5m and 6.5m everyday. The dairy averaged diffused attenuation coefficient spectra and underwater reflectance spectra were calculated. The results were compared with the absorption spectra of filtered samples obtained by validation cruises, which carried out 5 times during the moored period. Also, the natural fluorescence of chlorophyll a were extracted from the upward radiance spectra observed at 1.5m depth. The seasonal variation of the calculated attenuation coefficient spectra and the natural fluorescence were examined. The result shows a weak blooming of phytoplankton on November and a large blooming on April.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2002.04a
• /
• pp.179-182
• /
• 2002

The objective of this study was to evaluate petroleum hydrocarbon degradation processes governing natural attenuation at tile contaminated site and accomplished through conducting on investigation of degradation rate, capacity, and mechanism of the monitored natural attenuation. The monitoring results of the three years indicated that the concentrations of DO, nitrate, and sulfate in the contaminated area were significantly lower than these in the none-contaminated area. The results also showed a higher ferrous iron concentration, a lower redox potential and a neutral pH in the contaminated groundwater, suggesting that biodegradation of TEX is the major on-going process in the contaminated area. However, reduction of TEX in the groundwater was not only biodegradation but also dilution and reaeration during infiltration of uncotaminated surface and groudwater.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2001.04a
• /
• pp.128-131
• /
• 2001

We evaluated natural attenuation of petroleum hydrocarbons in a shallow aquifer using a modeling study. The studied shallow aquifer was severely contaminated with petroleum hydrocarbons, especially toluene, ethylbenzene and xylenes (i.e, TEX). The exact spill history was not known. Therefor we used a contaminant level in May 1999 (the first sampling date of our integrated study) as an initial contaminant concentration. we calibrated required transport parameters using the contamination levels obtained from groundwater analyses in September of 1999. For fate and transport of the petroleum contaminants, five case 2 with sorption and degradation. case 3 with sorption and degradation (half decay constant compared with case 2), case 4 with degradation but no sorption, and case 5 with sorption but no degradation. For sorption and degradation, a linear sorption isotherm and first order irreversible decay was assumed, respectively and no additional contamination source to groundwater is also assumed.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2005.04a
• /
• pp.371-374
• /
• 2005

We accomplished optimization for pump and treat (P&T) designs in consideration of degradation processes such as retardation and biodegradation, which are significant for contaminant fate in hydrogeology. For more desirable remediation, optimal pumping duration and minimum pumping rate constraint problems are studied. After a specific P&T duration, it replaces the P&T with the enhanced natural attenuation (ENA), which induces aerobic biodegradation by maintaining oxygen concentration. The design in this strategy carries out the optimization for the number and locations of oxygen injection wells.

• Journal of Environmental Impact Assessment
• /
• v.25 no.5
• /
• pp.333-344
• /
• 2016

In this study, the efficiency of natural attenuation was evaluated through the hydrogeological characteristics such as monitoring and analyses, tracer tests, chemical composition analysis of the groundwater at a military site contaminated by petroleum hydrocarbon in korea. Also, based on the results, the natural attenuation rate by distance and the expressed biodegradation capacity(EBC) was evaluated. The regression slope of -0.0248($K/V_x$) and bulk attenuation rate of $1.7{\times}10^{-3}/day$ were calculated respectively. The range of total expressed biodegradation capacity(EBC) of BTEX was shown from 9.1 mg/L to 10.0 mg/L(average 9.7 mg/L). It was confirmed that the denitrification which was expressed about 63.6% in the total EBC is the largest influence redox process. Consequently, the biodegradation capacity is considered to be sufficient for remediation in the BTEX average concentration of 1.326 mg/L.

• Nuclear Medicine and Molecular Imaging
• /
• v.42 no.2
• /
• pp.112-117
• /
• 2008

Artifact corrections including normalization and attenuation correction were important for quantitative analysis in Nuclear Medicine Imaging. Normalization is the process of ensuring that all lines of response joining detectors in coincidence have the same effective sensitivity. Failure to account for variations in LOR sensitivity leads to bias and high-frequency artifacts in the reconstructed images. Attenuation correction is the process of the correction of attenuation phenomenon lies in the natural property that photons emitted by the radiopharmaceutical will interact with tissue and other materials as they pass through the body. In this paper, we will review the several approaches for normalization and attenuation correction strategies.