Risk management for waste disposal sites and the leakage prevention of hazardous chemicals are quite important issues to improve the subsurface environment system including soil and groundwater. The existing techniques for monitoring and controlling chemicals in waste landfills are summarized to clarify the breakthrough for the future research and development. Considering the problems in waste sites and the urgent situation of leakage or spill of hazardous chemicals, we are developing the advanced barrier system for control of hazardous chemicals. The system consists of the active electrochemical barrier for detecting and cleaning contaminants, the soil metamorphic physical barrier, and the high precision technique for monitoring contaminant transport.
The developed techniques will be applied to subsurface environment for controlling hazardous chemicals and for repairing contaminated soils. In addition, the numerical model for predicting contaminant transport and assessing barrier techniques has been developed, using the original concept of multiphase fluids with physical and chemical interactions between solution and porous media.

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Soil and groundwater pollutions are caused by infiltration of hazardous organic liquids into soil due to illegal dumpings and inappropriate storages. The object of this study is investigating the behavior of non-aqueous phase liquid (NAPL) in soil and ground water.
First, one dimensional column experiments are carried out for various NAPL with glassbeads layer as porous media. The experiment includes measuring infiltration rate and vertical distribution of NAPL and water after NAPL movement stops.
Second, capillary pressure-saturation (P-S) relations needed in the mathematical model is measured and compared with that calculated by the method of Lenhard & Parker (1988). As a result, for various NAPL, P-S relations in air-NAPL systems can be caluculated by P-S relations in air-water systems but P-S relations in air-NAPL-water systems can not be calculated in a small saturation area because of trapped NAPL. Then, an amount of residual NAPL in suspended water zone is measured and relations between residual NAPL saturation and properties of NAPL and porous media is investigated.

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The trace elements leached from coal ash generated from coal-fired power plants migrate or diffuse into the surrounding soil and groundwater when the coal ash is disposed of in landfills. Boron, one trace element in coal ash, has a higher mobility in the underground than the other trace elements, because the main chemical form of boron has no electrical charge. Therefore, it is important to clarify the adsorption and migration behavior of boron in the underground environment. In this study, the adsorption of boron by soils was examined using three different methods: a batch method, a small-column method, and a large-column method called a lysimeter. The results showed that the adsorption isotherm conformed to the Henry type, and that the boron adsorption did not depend on the experimental method as well as the coexisting ions. However, the amount of boron adsorbed was pH-dependent and showed a maximum value in the weakly alkaline region. The above findings indicate that the migration characteristics of boron can be evaluated by the distribution coefficient obtained by the simplest batch method, when the boron concentration is less than approximately 20 mg/L and the pH is constant.

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One of recent serious environmental issues is soil and groundwater contamination caused by inappropriate storage, treatment and disposal of municipal and industrial waste materials. When a contaminated site is discovered, environmental risk to the surrounding area is immediately assessed and remediation measures have to be planned to minimize the expansion of the contamination. For performing this procedure effectively, it is necessary to systemize serial investigation processes including studies of contamination sources and underground expansion of hazardous materials, environmental risk assessment, and selection/recommendation of remediation methods. In this paper, a diagnosis system for effectively conducting the investigation processes is presented, and the role of computer simulation is focused as a tool for selection and evaluation of remediation alternatives in the system.

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The surface-subsurface-coupled,2-phase,3-dimensional fluid flow simulator was applied for numerical simulation of surface and groundwater flow in the vicinity of underground oil storage plant (Koji Plant).
Complex geological, hydrological and hydrogeological structure conditions, and various artificial factors such as storage caverns and tunnels were all considered in this model. The simulation was carried out incorporating the excavation of the caverns and all other works such as oil-in operation. A large amount of geological, hydrological and hydrogeological information have been acquired around the plant since the preparatory stage of construction. These information were considered thoroughly on the development of the simulation model.
Various observed data such as inflow rate into the tunnels and caverns, injection rate into the water sealing tunnels, river flow rate and groundwater level in the borehals were matched in time series with the calculated values in order to optimize this simulation model.
Satisfactory matching was obtained between measured and calculated values by the simulation. The hydrological and hydrogeological simulation model developed in this study is capable of representing the various conditions of the surface and groundwater flow over the long term from the stage of construction to the stage of operation. It is considered that this model is sufficiently accurate for use in predicting the surface and subsurface flow around the Kuji plant in the future. The results have led to useful understanding of the mechanism of subsurface flow.

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This paper describes the design of a new ventilated chamber system for continuous measurement of both the evaporation rate and the energy balance components at the bare soil surface with some of its principle advantages and characteristics. The influence of the used equipment on both of the temperature of the air and its relative humidity was studied and minimized. The air velocity inside the chamber has been regulated to be a logarithmic function of the height above the soil surface. The change of static pressure within the chamber compared with the ambient pressure was modeled well as a linear function of the volumetric flow rate of the air. A new method was proposed to estimate the diurnal variation of the net radiation, latent heat, sensible heat and soil heat fluxes at the bare soil surface. Twenty four hours in-situ measurement was carried out at Rokkasho Low-level Radioactive Waste Disposal Center, Aomori Prefecture, Japan, to check the operational effectiveness of the new device and the reliability of the proposed method for experimental periods of many days. Also, an accurate estimation of the evaporation rate from the soil surface for such type of places is indispensable, for evaluating safety concerning radioactive wastes. The value of the evaporation rate from the ground surface is necessary for the simulation of the ground water flow near the surface. The downward net radiation flux, the air temperature, the air relative humidity, the air velocity and the soil temperature just beneath its surface were measured continuously through the day of the field * Doctoral Student, Graduate School of Science and Engineering, Saitama University, Japan. ** Professor, Faculty of Engineering, Saitama University, Japan. *** Civil and Architectural Engineering Department, Japan Nuclear Fuel Limited, Tokyo, Japan. experiment. The evaporation rate, the latent heat flux, the sensible heat flux and the soil heat flux were calculated from the measured data. To check the accuracy of this new method, the soil heat flux was measured directly with two soil heat flux meters through a part time of the field experiment. A comparison between the measured values and those have been resulted from this method was made. Also, the transient change of the total percentage of error was calculated through the period of the soil heat flux measurement. The obtained results give a strong indicator that this method is suitable for estimating the energy balance components at the bare soil surface. This new method has the advantage of that it needs only simple data and it wears an aspect of certainty.

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When released from the ground surface or a source above the capillary fringe, a Dense Nonaqueous Phase Liquid (DNAPL) migrates downwards as a distinct fluid to the fringe. If the rate of the release is relatively low, accumulating and spreading behaviors of the DNAPL upon the fringe will be clearly observed. Such behaviors relate to dynamics of the critical depth of accumulated DNAPL just beyond which the DNAPL starts to finger through the air-water interface (top of capillary fringe). This parameter, in turn, is determined by the threshold entry pressure and water capillary rise height. Many formulas have been developed for estimating capillary rise height and threshold entry pressure, respectively. However, limitations in application are recognized such as some formulas are difficult to apply, others give overestimated results, etc. And a confuse of threshold entry pressure for critical depth may happen because the role of capillary rise height seems to be ignored in all formulations. This paper reports an approach dealing with the problems identified above, in which both the definition and role of all three parameters are made clear, and new formulations are developed to overcome the limitations of available formulas. The approach provides results agreed with experimental results obtained in this study, as well as the data from literature.

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