In estimating areal extent of groundwater pollution, and making remediation plan, it is useful to depict convection/diffusion behavior of contaminants in subsurface by numerical simulation. However, conventional Eulerian-Lagrangean formulation for solute transport cannot be applied to recent problems of contamination by insoluble materials such as VCOs, oil, etc., because multi-phase flow occurs.
Focusing on developing a comprehensive platform of simulation that can treat groundwater pollution problems caused by various types of chemicals, a set of multi-phase, multicomponent equations is proposed. It expresses air-water-contaminant 3-component,3-phase flow with adsorption/desorption, dispersion, and mass exchange between fluid phases, so that it covers from single-phase solute transport to multi-phase flow caused by insoluble contaminants.
The equations are incorporated in a 3-D numerical simulator which utilizes flexible corner-point FDM as the basic frame of discretization, and is capable of dealing with natural geology/topography, heterogeneity of rocks, and various initial/boundary conditions. The validity of the developed simulator is checked through the results of 1-D and 2-D model studies.

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The Saga Plane, which is located in the south of the Saga Prefecture, has a coastline to north of the Ariake Sea. The top layers of this plane consist of very soft cohesive layers. The groundwater in this plane has been used for water service, agricalture and industry. Then, land subsidence induced by groundwater pumping is very serious problems in this plane. The settlements observed from 1971, are of the order of 30cm in Saga district and lm in Shiroishi district.
In 1994, the Saga Plane experienced the smallest rainfall for the last 100years, with the maximum temperature of 39.6°C beyond the previous record level of 38.0°C. In Shiroishi district, the ground water level fell by about 18m due to water shortage and greate demand of groundwater in 1994. Consequently, the rate of subsidence accelerated as high as 16cm/ year.

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[in Japanese]

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