Water samples from 52 shallow wells and 2 rivers in the Tonami plain (Shogawa fan), Toyama, were sampled for chemical analysis, ¹³C/¹²C measurement of the dissolved carbonate and ¹⁸O / ¹⁶O analysis of the water. Wells far from the area of recharge from the rivers have δ¹³C values of -19 to -21‰ and total carbonate contents of upto 3 mmol/l, whereas the rivers have δ¹³C values of -8 to -9‰ and total carbonate contents about 0.5mmol/l at the recharge area. The relationship between the δ¹³C value and total carbonate content indicates that the additional carbonate is of soil CO₂ origin. The partial pressure of CO₂ in the aquifer estimated from the total carbonate content and pH of the groundwater amounts upto about 3×10^-2 atmosphere, 2 orders of magnitide higher than the atmospheric value, supporting that the additional carbonate is derived from the soil CO₂. The.δ¹⁸O value of groundwater increases, as the δ¹³C value decreases away from the recharge area, implying that a significant amount of precipitation percolates into the aquifer through the soil zone. The rela-tionship between the HCO₃^- and Ca²⁺ Mg²⁺ contents of the groundwater suggests that the dissolu-tion of soil CO₂ to the recharge water of precipitation origin results from reaction of soil CO₂ with Ca (OH)₂ and CaSiO₃ which are widely used for artificially neutralizing the acidified soil.

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The tritium concentrations in rain water collected in Fukuoka, Japan, from April 1987 to July 1991, were measured with the combination of low-level liquid scintillation counting and electrolytic en-richment of tritium in water. The tritium concentration of each rainfall (264 samples) showed the large fluctuation from 0.06 to 3.39 Bq/l. The tritium concentration in rain was significantly affected by the weather conditions. The frequency distributions of tritium concentrations in rain water were shifted to higher side in March, April, May and December. Higher tritium concentrations than 2.0 Bq/l were observed only in March, April and May, when air mass moved dominantly from the Asian Continent to Fukuoka. The annual average concentrations were no longer decreased after 1987 in Fukuoka.

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In order to estimate a long term chemical change of groundwater and streamwater by acid deposi-tion, it is necessary to know both the pathway and concurrent chemical change of precipitation in a watershed. We observed temporal variations in the chemistry and isotopic composition of the ground-water and streamwater in a mountainous watershed during a storm. Based on these observations, we divided groundwater and streamwater into 3 components; precipitation, soilwater, and groundwater. By reproduction of streamwater and groundwater chemistry using this result, this separation method is proved to be effective for making a prediction model of streamwater and groundwater caused by acid deposition. Key words : Acid Deposition, Isotopic Composition, Streamwater and Groundwater Chemistry, Runoff components

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Hydrogen and oxygen isotope ratios of meteoric waters in Okayama Prefecture collected in 1990 to 1992 are reported. The δD and δ¹⁸O values of precipitation collected at Okayama University, Okayama City, vary in the wide ranges from +20.0 to -123.0‰ and from 0.0 to -17.0‰, respec-tively. Precipitation in the rainy season (June and July) has distinctly lower δD and δ¹⁸O values than in the other seasons. The weighted averages for a year from July, 1991 to June, 1992 are δD=-53.0‰ and δ¹⁸O=-8.1‰ with a d parameter of 11.8‰.
River waters are uniform both in δD and δ¹⁸O values and they range from -47.8 to -58.7‰ and -7.9 to -9.1‰, respectively, with the average δD value of -51.9‰, δ¹⁸O value of -8.6‰ and d parameter of 16.9‰, which indicates the river waters of Okayama Prefecture are just on the meteoric water line of Japan. The difference in d parameter between the average precipitation and the average river water may be explained by significant contribution of precipitation with high d para-meters in northern Okayama Prefecture to the river waters. Most well waters show deviations from the meteoric water line of Japan, indicating kinetic isotope effects during evaporation. The Yubara hot spring waters have the same δD and δ¹⁸O values to the nearby Asahigawa river water.

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The numerical analysis is commonly used to predict the behaviour of subsurface water in the layered unsaturated natural slopes or the compacted soil embankment with the geofilter. To analysis this kind problem, unsaturated properties of the soil and geofilter have to be obtained. So the methods of determination of unsaturated properties for soils have been developed in these ten years. But the method of determination of unsaturated properties for. geofilters has not been established yet.
In this paper, a measuring method of hydraulic properties for unsaturated geofilters is proposed. And this method is applied to high permiable materials, that is, gravels and geotextiles.

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