In Lake Kasumigaura where paleohydrologic information during the period of sedimentation may have remained, two-dimensional unsteady groundwater flow simulation was made in vertical cross section while considering such long-term transitions as sea level change, changes in salinity and sedimentation. As a result, the depth profiles of salinity in pore water extracted at two core drilling sites that were obtained in existing works were reproduced, the difference in contribution of local fresh groundwater at both sites was indicated. The simulation revealed that Site K-1, which is close to the lakefront, was affected by local fresh groundwater as well as surface water, but Site K-2, some way distant from the lakefront, was unaffected by the local fresh groundwater. By unsteady groundwater flow simulation, the transition of the more detailed hydrological environment was revealed.

To understand distribution of the atmospheric SF₆ mixing ratio is vital for groundwater dating using SF₆. Monitoring of the atmospheric SF₆ ratios were conducted at three major metropolitan areas and one rural area, to clarify spatial distribution of the atmospheric SF₆ in and around urban area in Japan. All the measured values exceeded Northern Hemisphere clean air levels. The average excess ratios were 102% in Tokyo, 53% in Osaka, 30% in Nagoya and 15% in Chubu mountainous area. These excess causes an underestimate from 3 to 17 years in apparent SF₆ age, suggesting that adjustment of the input air curve is necessary when the SF₆ method is applied to the groundwater dating in Japan.

A high concentration of chloride ions was detected from the groundwater in hilly and mountainous areas of the Chugoku Region. An electric water heater, which had used this high chloride groundwater, failed after a short term due to corrosion, etc. In general, low corrosive metals, such as copper, are used for electric water heaters. Thus, the relationship between the cause of failure and the high chloride concentration is considered to be close. In this report, firstly, we showed the relationship between the high concentration of chloride ions included in groundwater and the cause of the failure of an electric water heater. Simple corrosion tests were carried out to estimate the relationship between the lifetime of copper and the degree of corrosion affected by the chloride concentration. As a result, it was found that corrosion may occur in corrosion-resistant copper in ten years under high temperature and high humidity conditions even if the chloride concentration is about 20 mg/L.