The purposes of this study are (1) to describe the extent of boron contamination of groundwater in the Central Boso Peninsula and (2) to identify possible sources of the contamination. Out of 147 samples, boron concentrations of 21 samples exceeded the former guideline value of 0.2 mg/L. The contaminated wells are distributed locally. The groundwater with high boron concentrations has characteristics of higher values of Na, K, and HCO₃ concentrations, pH and EC, extremely lower value of Ca concentration and brownish colored water. The contaminated water is classified into two types of water, noncarbonate alkali and carbonate alkali types, whose contaminant sources are estimated as fossil water and marine sediments of deep layers, respectively.

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Air-liquid interfacial area (α_i) is an important parameter in the subsurface hydrology that describes the pore scale distribution of air and liquid inside the porous media. In order to quantify this parameter, a theoretical model using soil characteristics (ψ-θ) curve was developed by introducing a term“hydraulic radius”for the pores inside the medium. This term diminishes the effect of any shape of the pore. The derivation becomes a simple expression which needs only drainage soil characteristics curve. In this study,ψ-θ curves were developed experimentally for three glass beads media (0.25mm,0.50 mm and 0.75mm) and the theoretical method was applied successfully to estimate the parameter, α_i in these different porous media. Results obtained by this method follow the general concept of decreasing α_i with increasing liquid saturation. They also show that the α_i is increasing with decreasing grain size, which supports the frequency distribution of the pore sizes inside the porous media. Estimated air-liquid interfacial area was also compared with the results obtained by an experimental technique using surfactant mass extraction. Comparison of the results shows that the interfacial area determined by this theoretical method provides reasonable estimation. Finally, the method was applied to a sand mixture (d₅₀=0.25mm) to estimate the air-liquid interfacial area and was compared with the experimental results of interfacial tracer technique as described by Kim et al., (1997). Results found by comparing α_i of solid surface area at zero saturation revealed that the theoretical method provides reasonable estimation of α_i than the interfacial tracer technique.

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This paper gives some introduction to inverse analysis of regional aquifer models. The inverse analysis problem attracted interests of many researchers of vatious field in 1980's 1990's. Throughout this period, the essential issues and the solving procedure of the inverse problems have been widely recognized and shared by the people working in this area. For this reason, the general aspect of the inverse analysis procedure is explained in this paper. The essential issue in the problem is ill-posedness. This concept is explained in detail. A way to overcome this problem is regularization procedures, and several different ways are presentd, i. e. the minimum norm solution, the prior mean minimum norm solution and the extended Bayesian method. At the final part of this paper, these points are illustrated by figures.

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