A critical review on climate changes and g roundwater has been made from the point of view of global studies on groundwater. Groundwater recharge, groundwater discharge, effects of sea level rise, groundwater storage, effects on groundwater quality and subsurface temperature, and methodologies have been discussed. International projects such as GRAPHIC (Groundwater Resources Assessment under the Pressures of Humanity and Climate Changes) project are also introduced for global studies on groundwater.

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According to IPCC, global warming may b ring about rise in mean sea-level by 9cm - 88cm at the end of 21^st century. Because the Japanese archipelago is surrounded by sea and important socioeconomic activities concentrate in areas below sea-level, it is prerequisite to predict influences of sea-level rise on groundwater systems in coastal aquifers. By conducting laboratory experiments, impacts of sea-level rise on coastal groundwater systems were investigated together with the effect of conservative measures. These experiments are specially characterized by the domain of glassbeads with inclined surface, which allows surfacial ponding of water and installation of an impermeable barrier in the domain to set back salt water intrusion. By these experiments, it is revealed that the sea-level rise causes acceleration of salt-water intrusion in coastal aquifers and inundation of low-lying areas, and that impermeable barriers are effective for preventing salt water intrusion but at the expense of inundation.

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Laboratory experiments were conducted to measure P-wave velocity and deformation strain changes during injection of CO₂ into water-saturated Tako sandstone. The rock sample was cylindrical, with its axial parallel to the bedding plane, and fluids of water and CO₂ were injected from bottom end of the sample. P-wave velocity changes caused by CO₂ injection are typically about -10%, and -16% for the injection of supercritical CO₂. Such changes in velocity show that the seismic monitoring method is useful in mapping CO₂ movement in aquifers. Strain measured normal to the bedding plane was greater than that parallel to the bedding plane during CO₂ injection. In the case of supercritical CO₂ injection, bedding plane showed a strong effect on strain measurement. Such strain changes suggest the possibility of monitoring rock mass deformation by using borehole tiltmeters at geological sequestration sites.

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Chemical and mineralogical compositions of groundwater and country rocks in sedimentary an d granitic rock areas in Hakushu area, Yamanashi Prefecture are distinctly different. Anion (Cl^-, SO₄^2-) concentrations in the sedimentary rock area are higher than those in the granitic rock area due to the influence of fossil seawater, but cation concentrations are not different and pH is higher. Saturation index for calcite in groundwater in the sedimentary rock area is higher than that in the granific rock area, suggesting groundwater chemistry of the sedimentary rock area is influenced by the dissolution of calcite.

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The carbon fixation by water-rock reactio n s (mineral trapping) in the sequestration of carbon dioxide into the aquifer is investigated based on dissolution kinetic model. The simulation is performed by using the mineralogical and chemical data of the host rocks (sedimentary and igneous rocks) and formation water (freshwater and saline water) in the Boso Peninsula, Chiba, Japan and injecting a constant CO₂. The model result indicates that mineral trapping is successful for fixation of carbon as carbonate minerals in hundred thousand years in the cases for not only sedimentary rocks (mudstone and sandstone) but also igneous rock (serpentinite). The proportion of the amount of fixed carbon to the injected CO₂ into the groundwater becomes larger as the amount of the carbonate minerals in host rock and/or of the released Ca' and Mg2+ by dissolution of silicate minerals is smaller. However, the proportion is not significantly influenced by chemical composition of initial groundwater and grain size. It indicates that it is important for CO₂sequestration into the aquifer to confirm the amount of carbonate minerals and silicate minerals including Ca²⁺ and Mg²⁺ in host rocks. Concerning the time scale to fix carbon as carbonate minerals, it is estimated that it takes approximately 10⁵ years to complete the mineral trapping when field dissolution rate constant data are used.

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In order to characterize of hydrogeologica l condition at a scale of several kilometers by using groundwater flow modeling, it is important to set groundwater flow modeling area and its boundary conditions adequately. Therefore it is efficient and useful to detect the groundwater flow system includes the area from the recharge area to discharge area. The groundwater flow system through deep underground is to be mainly affected by hinterland, large faults and groundwater table distribution. In this study, therefore, three dimensional groundwater flow modeling taking account of these influences was performed in some areas having different scale to identify groundwater flow system through deep underground.
From the results, t he groundwater flow system could be identified, and the modeling area and its boundary conditions have been able to set at a scale of several kilometers adequately.

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In order to study the origin of phosphorus in the river waters, the concentration and the source of the phosphorus and vanadium in the underground waters, springs as well as river waters at the foot of Mt Fuji, Mt. Yatsugatake and Kofu basin were investigated. The phosphorus and vanadium concentrations in the underground and spring waters in these areas were classified into three groups, and show a positive relationship between phosphorus and vanadium concentration in them. Furthermore, both of these elements concentrations in the samples are the highest at the foot of Mt. Fuji area, become gradually lower at the foot of Mt. Yatsugatake area, and Kofu basin area.
The ratio of phosphorus to vanadium concentration (phosphorus/vanadium ratio) of underground and spring waters were also classified into three groups. The ratio of the samples in Mt. Fuji area is smaller than that in Mt. Yatsugatake and Kofu Basin area. The phosphorus/vanadium ratio obtained from these water samples is also similar to those estimated for rocks distributed in each of these areas; Mt. Fuji, Mt. Yatsugatake and Kofu Basin. Based on these regional differences of phosphorus and vanadium concentrations and phosphorus/vanadium ratio, it is suggested the phosphorus and vanadium concentrations in the underground and spring waters are characterized by the geochemical effects of the rocks and strata such as basaltic, andesitic and granitic rocks that are dominant in the area.
The characteristic s of phosphorus and vanadium concentrations and their ratios obtained in the Sagami River is essentially similar to those of the underground and spring waters come from around and upper part of the river. Therefore, the origin of phosphorus and vanadium concentrations of the Sagami River were essentially explained by geochemical effects from the rocks and strata distributed the area along the river. However, phosphorus concentration of the Sagami River is slightly higher than that of the underground waters and/or springs upper part of the river.
The vanadium concentration obtained in the Fuji River is also similar to the concentration of underground and spring waters around and upper parts of the riven On the other hand, the phosphorus concentration and phosphorus/vanadium ratio in the Fuji River is extremely higher than that of the underground and spring waters come from around and upper part of the river.
It seems that the phosphorus concentrations of the Sagami and Fuji Rivers is explained by the migration of phosphorus concentrations from underground and/or spring waters come from around and upper part of the river and by the excess phosphorus concentrations. The total phosphorus concentration of the river waters comes from the combination of underground, spring water concentrations and excess phosphorus concentration by artificial effects. The artificial excess phosphorus concentration was calculated by subtracting the underground and spring water concentration from the total concentration in the river waters. Accordingly, it is possible to estimate the excess phosphorus concentration of river water by the help of both the phosphorus and vanadium information of underground and spring waters in the area.

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Ikeshima Coal Mine was closed in Nov e mber 29^th,2001, after 42 years of operation. The pining area was in the southwest of the Ikeshima Island. The drainage increased as the min ing areas extended, creating problems in both production operation and safety. The waters of dr ainage Ind flood in the mine have characteristics that (1) the rate of drainage decreases, (2) the c hemical omponents of the water in the floods do not change much with time but (3) they differ locally. Ile results of the investigation show that (1) the drainages in this mine are classified into 3 types by the combination of dissolved ions, (2) water eruption decreases exponentially, and (3) the southwest area of Ikeshima Island, the western area of the main drifts, is estimated to have hu ge eater bearing areas.

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