Heterogeneous solute transport in a soil is often described with the mobile-immobile model (MIM). Although the mobile phase fraction, θ_m /θ, and the exchange rate coefficient between the mobile and immobile phases, α, cannot be determined independently, the MIM is flexible to fit various nonequilibrium solute transport by optimizing θ_m /θ and α. Two examples were discussed as the MIM applications: an aggregated Andisols and a nonaggregated dune sand, demonstrating equilibrium transport in a saturated aggregated soil, and nonequilibrium transport in an unsaturated dune sand. The MIM can be further applied to diffusion-controlled adsorption and mixed aerobic and anaerobic conditions in an aggregated soil.

To understand the influence of earthquakes on hydrochemical compositions of groundwater particularly for trace metals，water samples were collected from 16 representative spring sites after the occur rence of the 2016 Kumamoto earthquake near the epicenter and fault zone. Among multiple elements measured in this study，Al，Fe，Mn and V increased their concentrations just after the earthquake and subsequently declined for some springs. Our observations suggest that seismic shaking enhanced release of Al，Fe and Mn as colloidal matters that led concentrations of these elements increased in groundwater. Similar increase in concentrations was confirmed for V that might be triggered by disso lution of rock materials. These observations seem to be explained by both mitigation of colloidal release and dilution by groundwater with relatively low concentrations. Our survey showed that the disturbed hydrochemical signatures is suggested to be returned to steady state in annual hydrological cycle.

Fluorescent dyes have been commonly used as tracers to track the water movement. However, the cases of significant decrease in concentration had been observed when they were added to groundwater. In this study, we investigated changes in the concentration of fluorescent dyes when they are added to water samples and examined the mechanisms. Sodium fluorescein (uranine) and sodium naphthionate (NAP) were found to decrease significantly when they contact with groundwater, in some cases. These were suggested the microbial influence on the decrease in the concentration of these dyes. The results have shown that the micro bial activity can cause a significant decrease in the concentration of these dyes. Based on our findings, points to be considered when using fluorescent dyes as conservative tracers are summarized. Finally, we proposed an appropriate sample storage method for the analysis of fluorescent dyes concentrations.

This paper discusses regional groundwater flow and water quality in a confined aquifer of the G 1 layer distributed throughout the Echigo Plain. The G1 layer is distributed near the ground surface in Nagaoka and reaches a depth of 160 m in Niigata City. The current survey showed groundwater flows relatively actively in Nagaoka, which recharges the G1 layer and flows northward. North of the plain, it was revealed that the high Cl^－ concentration groundwater, which is distributed in Tsubame, Sanjo, and Yoshida, included old groundwater recharged during the last glacial period and young groundwater less than 70 years old. Therefore, new groundwater recharged the aquifer where old groundwater was distributed, and the existence of marine deposits greatly influenced the water quality. The older groundwater possibly remained in the G1 layer due to the decreasing hydraulic gradient from the sea level rise that occurred after the last glacial period ended, and impermeable strata produced by transgression covered the G1 layer.

Hydrogen and oxygen isotopes and tritium (³H) analyses of hot spring waters from three locations in the Kuzu Hot Spring area at the eastern foot of the Northern Alps were carried out to estimate the origin, flow mode and heat source of the hot spring water. The Kuzu hot spring was an intermediate type of sodium chloride and sodium bicarbonate. Based on the results of tritium, hydrogen, and oxygen isotope analyses, the hot spring water was of meteoric water origin, at least prior to the late 1980s, and precipitation that fell in the surrounding mountainous area. It was presumed that the water is heated in the Pliocene granitic bodies as it infiltrates underground, and then flows out of the highly permeable layers along the Takase River.