We developed a numerical method (ASG method) for simulating a coupled atmospheric gas–surface water system, simulated by Navier–Stokes equations, and groundwater system, simulated by water saturation equations. Here, we derived dimensionless formulas for ASG method to avoid the influence of a dimension of analytical domain, in this study. Further we used the ASG method to simulate the configuration and movement of the infiltration front in an embankment composed of sand and obtained results similar to those obtained by a water tank experiment in another study. In addition, in a practice problem using non-dimensional values, we simulated the movement of gas and water when surface water flowed over an embankment expressed in dimensionless form.

Consequently the ASG method could simulate the movement of water and gas across the interface between a surface system and a porous medium including the practice embankment.

In contamination evaluation methods using luminous bacteria against groundwater or soil contamination by heavy metals, there is a possibility of being influenced by the heavy metal nanoparticles. Conversely, the acute toxicity evaluation methods using luminous bacteria may be available for toxicity evaluation of the nanoparticles. In this study, effects of nanoparticles on luminous bacteria (Vibrio fischeri) were investigated using commercially available dispersions of carbon nanotubes (CNT), Ag nanoparticles and several types of metal oxide nanoparticles. In the results, CNT and SiO₂ nanoparticles were verified to have no acutely toxic effects on the luminous bacteria. The acute toxic effects of Ag nanoparticles could not be evaluated because the influence of dispersant could not be removed. On the other hand, Al₂O₃, TiO₂, ZnO, CuO nanoparticles were found to have the acute toxic effects.

This study estimated required borehole heat exchanger lengths in ground source heat pump systems for an assumed residence to minimize the life cycle costs considering groundwater flow effects. As a case study in Morioka City, Area 3 among 7 climate areas in Japan, the estimated lengths decreased as the logarithms of Darcy velocity increased between 10 and 200 m/y. The lengths were converged when the velocity was over the range in both large and small effective thermal conductivities. The results were also dependent largely on the heating/cooling loads, indicating the differences among the comparison areas. The target reduction ratios of the initial cost indicated that the systems were possibly economical relative to the conventional systems in the cold Areas 1 and 2 even when the Darcy velocity was neglected, and in the moderately warm Areas 3 and 4 when the Darcy velocity was over 100 m/y.

Repeated measurements of subsurface temperature-depth profiles have been conducted eight times between May 2000 and December 2015 at the Kawaguchi groundwater observation wells in southeastern Saitama Prefecture, Japan to evaluate distribution and causes of subsurface warming in an urban area. Additionally, monitoring has been conducted since April 2007 to observe long-term changes in subsurface temperature. Subsurface warming was observed at depths shallower than 40m. Subsurface warming decreased with depth, and at depths of 20m, 30m and 40m had rates of 3.4×10^{-2 o}C/year, 2.30×10^{-2 o}C/year and 1.93×10^{-2 o}C/year, respectively. Results of comparison between calculated temperatures and observed temperatures indicate that surface warming estimated by secular changes in air temperature, starting in 1983, has led to subsurface warming that has been observed after 2003.

This study conducted an evaluation of hot spring discharge using five groundwater drainage wells in Hikaruma District of Matsunoyama, Tokamachi City, Niigata Prefecture. The samples collected from two groundwater drain wells were Na–Cl type water and had heavier oxygen and hydrogen isotope ratios than the other samples. The isotope ratio results indicated that the two samples formed by mixing between hot spring water and groundwater originated from meteoric water. An evaluation of the mixing ratio of the hot spring water and the groundwater originated from meteoric water, with a two-component mixing model using Cl⁻ concentration, showed that the mixing ratio of hot spring water was approximately 5 to 14%. When the mixing ratio was multiplied by the drainage amount of the two groundwater drain wells, the annual hot spring discharge from the two groundwater drain wells was estimated to be approximately 4.5×10⁵ L.

A geothermal exchange unit has been developed to reduce the capital costs of ground source heat pump systems. Its source of heat energy is shallow groundwater. The geothermal exchange unit comprises flexible containers, sheets of heat exchanger and gravel of high permeability. The sheets of heat exchanger run helically through flexible containers in the unit with gravel. Demonstration experiments in the Kurobe alluvial fan proved that the unit can be installed up to GL-3 m by excavating with heavy equipment. The result of demonstration experiments showed that the average and the standard deviation of cooling outputs are 3.1 and 0.8 kW, respectively. Furthermore, this study selected a candidate area for unit installation based on the depth limit of excavation with heavy equipment and the water table. In result, this study proved that the unit can be installed in the fan toe with water table and high Darcy velocity.