• Journal of Soil and Groundwater Environment
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• v.8 no.3
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• pp.1-7
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• 2003

A modified model was developed for solute transport in porous media that can consider the movement of an LNAPL above the water table. From the results of sensitivity analyses with and without considering LNAPL movement, there are some differences according to the hydraulic gradient, the quantity of oil leakage and dispersivity. The mean deviation between the model in this study and a conventional model without LNAPL movement increases as the hydraulic gradient decreases and the quantity of oil leakage increases. Variation of dispersivity has no influence on the magnitude of the mean deviation. However, the spatial distribution of the deviation between the two models is wider as dispersivity increases. Furthermore, groundwater is at high risk of contamination in the vertical direction in the case that transverse dispersion value is large. A conventional model underestimates the concentration of solute in an aquifer where the movement of an LNAPL cannot be negligible: Based on the study results, it is important to understand how fast the LNAPL moves on the water table for realistic prediction of solute transport in an aquifer with the movable LNAPL on the water table.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1999.10a
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• pp.39-43
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• 1999

불포화대에서 LNAPL의 이동과 분포를 수치 모의를 통하여 예측하였다. 균질한 매질에서 LNAPL의 이동은 조립질 매질에서 빠르고, 세립질 매질에서 더 많은 면적으로 확산되며, 더 많은 LNAPL이 불포화대에 잔류한다. 조립질 매질내에 세립질층이 존재할 경우, 이 층이 지하수면으로부터 멀수록 LNAPL이 많이 포획된다. 조립질 매질에 세립질 또는 더 조립질인 매질이 렌즈 상으로 존재하는 환경에서는, LNAPL이 이들 렌즈를 통과하지 못한다. 불균질한 렌즈가 존재할 때의 LNAPL 분포를 초기조건으로 이용하여, 지하수 면의 수직 이동과 물의 침투에 따른 LNAPL의 이동을 모의하였다. 두 경우 모두 불포화대에 잔류되어 있던 LNAPL의 수직방향 이동이 증가되었다. 특히, 지하수면의 하강 시 LNAPL이 조립질 렌즈를 통해 이동하나, 세립질 렌즈를 통해서는 이동하지 못한다.

• Journal of Soil and Groundwater Environment
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• v.10 no.6
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• pp.63-67
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• 2005

Laboratory scale experiments were carried out to delineate the effects of liquid phases, such as soil water and light nonaqeous phase liquid (LNAPL) on the transport of gaseous ozone in unsaturated soil. Soil water enhanced the transport of ozone due to water film effect, which prevents direct reaction between soil particles and gaseous ozone, and increased water content reduced the breakthrough time of ozone because of increased average linear velocity and decreased air-water interface area. Diesel fuel as LNAPL also played a similar role with water film, so the breakthrough time of ozone in diesel-contaminated soil was significantly reduced compared with uncontaminated soil. Ozone breakthrough time was retarded with increased diesel concentration, however, because of high reactivity of diesel fuel with ozone. In unsaturated soil containing two liquids of soil water and LNAPL, the transport of ozone was mainly influenced by nonwetting fluid, diesel fuel in this study.

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.51-65
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• 2003

A series of numerical simulations were carried out using STOMP( Subsurface Transport over Multiple Phase) simulator. The flow and distribution of LNAPL were analyzed in homogeneous fine and coarse sand. Vertical movement of LNAPL is faster in the coarser sand. But the total volume of LNAPL retained in the unsaturated zone is larger in the finer sand. A fine layer in the coarse sand domain is also simulated. The results showed that the retained LNAPL volume and shape are highly influenced by the Position of the fine layer. Flow and distributions of LNAPL were simulated when there were heterogeneous lenses in the sand domain. Water table fluctuation was also considered. In these cases, it was found that the heterogeneous lens was a barrier to LNAPL flow, and water table fluctuation stimulated the downward movement of retained LNAPL. The LNAPL flow and distribution observed in these numerical experiments show that in the subsurface environment, the behaviors of LNAPL highly depend on heterogeneities of unsaturated zone and the dynamic hydrogeologic condition such as water table fluctuation. These results can explain some of the complexity of LNAPL flow and distribution Patterns in LNAPL contaminated field sites.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.282-284
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• 2003

Multi-phase extraction of LNAPLs not only floating on groundwater but also captured in soil pores was studied in a simulated soil system. The extraction rate of LNAPL under the MPE conditions was much higher than the rate under usual hydraulic gradient conditions. The WE might be especially useful for recovery of oils in fine-textured soils such as clay-dominant soils. The vacuum-enhanced transport of LNAPL in soils also depended on the properties of LNAPL such as viscosity and density as well as soil textures.

• Journal of Korea Soil Environment Society
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• v.2 no.1
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• pp.51-61
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• 1997

The objective of this study is to evaluate the feasibility of Pumping-and-Treatment system (PTS) for remediation of the saturated zones contaminated with NAPLs. A simulation is carried out for the removal of DNAPLs (denser-than-water non-aqueous phase liquids) and LNAPLS (lighter-than-water non-aqueous phase liquids) distributing at and below the water table. In the study, LNAPL and DNAPL are assumed to be n-hexane and 1,1-dichloroacetone, respectively. The model system studied consists of four heterogeneous soil layers with different permeabilities. Groundwater flows through the bottom layer and a pumping well is located under the initial water table. The time-driven deformation of the water table and removal efficiency of contaminants are estimated after vacuum application to the inlet of the well. In the calculation, FVM (Finite Volumetric Method) with SIMPLEC algorithm is applied. Results show that removal efficiencies of both DNAPL and LNAPL are negligible for the first 5 days after the PTS operation. However, when the cone-shape water table is formed around the inlet of the pumping well, the rapid removal rate is obtained since NAPLs migrate rapidly through the curvature of the water table. The removal efficiency of DNAPL is estimated to be higher than that of LNAPL due to the gravity. The results also show that the fluctuation or cone-shaped depression of the water table enhances the removal efficiency of NAPLs in saturated zones. The simulation results could provide a basis of the PTS design for the removal of NAPLs in saturated zones.

• Journal of Soil and Groundwater Environment
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• v.12 no.4
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• pp.25-31
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• 2007

Characterizing the risk posed by a mixture of chemicals is a challenging task due to the chemical interactions of individual components that may affect their physical behavior and hence alter their exposure to receptors. In this study, cell tests that represent subsurface environment were carried out using benz[a]anthracene (BaA) and p-xylene focusing on phasetransforming interaction to verify increased mobility and risk of highly sorbed pollutants in the presence of less sorbed, mobile liquid pollutants. A transport model was also developed to interpret results and to simulate the same process on a field scale. The experimental results showed that BaA had far greater mobility in the presence of p-xylene than in the absence of that. The main transport mechanisms in the vadose zone were by dissolution to p-xylene or water. The transport model utilizing Defined Time Steps (DTS) was developed and tested with the experimental results. The predicted and observed values showed similar tendency, but the more work is needed in the future study for more precise modeling. The field-scale simulation results showed that transport of BaA to groundwater table was significantly faster in the presence of NAPL, and the oral carcinogenic risk of BaA calculated with the concentration in groundwater was 15${\sim}$87 times larger when mixed with NAPL than when solely contaminated. Since transport rate of PAHs is very slow in the subsurface without NAPL and no degradation of PAHs was considered in this simulation during the transport, the increase of risk in the presence of NAPL is expected to be greater for the actual contaminated site.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1998.06a
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• pp.38-42
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• 1998

Soil venting이 오염토양중 가솔린의 용출거동에 미치는 영향을 정량적으로 예측하기 위하여 가솔린의 휘발과 용해거동이 Raoult의 법칙에 의해 설명되어 질 수 있는지를 평가해보았다. 먼저 순수 가솔린의 용해거동과 휘발거동에 대해 검토해 보고 이후 토양중 가솔린의 거동에 적용하여 보았다. 가솔린성분들의 용해거동은 휘발에 의한 성분조성의 변화와 상관없이 Raoult의 법칙에 의해 비교적 정확하게 예측될 수 있었으며 오차범위는 naphthalene을 제외하고는 최고 $\pm$ 100% 이내였다. 오염토양의 형태로 가솔린이 존재하는 경우에도 Raoult의 법칙에 의해 정확히 예측될수 있었으나 토양중 농도가 초기 20,000 mg/kg에서 1,360 mg/kg로 감소한 경우에는 용출농도가 예측치의 50-70% 수준으로 낮은 경향을 보였다. 한편 soil venting시 휘발에 따른 조성변화를 Raoult의 법칙을 이용하여 산정하고 각 성분조성에 대한 개별물질들의 용출잠재성을 결정하는 모델을 이용하여 실험결과와 비교하여 보았다.