For safety assessment of geological isolation, it is important to evaluate in situ redox buffer capacity in high-permeability zone as groundwater flow path. This study evaluated in situ sulfate reduction as redox buffer capacity in the conglomerate bedding in Toki Lignite-bearing Formation, which occurs at the lowest part of sedimentary rocks overlying basement granite. The bedding plays an important role as the main groundwater flow path. The result showed that in situ redox buffer capacity in the conglomerate bedding has been identified on first nine months, whereas in the following period the redox buffer capacity has not been identified for about fifteen months. This will be caused by the bedding became inappropriate for microbial survival as the organic matter which is needful for microbial activity was consumed. Thus, there will be limited redox buffer capacity in groundwater flow path even in formation including organic matter-bearing layer.
It can be recognized that water temperature of springs distributed on the northern foot of Mt. Asama has remarkable regional variations. The purposes of this study are to discuss the various formation mechanisms and the factors bringing about regional variations of spring water temperature. The results were summarized as follows: 1) Rokurigahara spring group which situated at the about 1200m altitude on the northern foot of Mt. Maekake (active younger volcano) is a discharge area of groundwater recharged on higher part, i.e. near the crater, of the mountain slope. For the influence of excessive geothermal heat by volcanic activity along the flow path, spring water temperature in this spring group is higher than that in the other ones. 2) Spring water temperature at the tip of Onioshidashi lava flow is extremely low compared with other regions. This low spring water temperature phenomenon may be caused by low temperature condition formed by wind-hole circulation in the lava flow with linked large open spaces. 3) Although the spring water temperature on the mountain slope generally decreases on the decline in altitude, the springs distributed on the northern foot of Mt. Maekake show a reverse trend, i.e., the water temperature of Rokurigahara spring group is comparatively higher than that of 1000m spring group. The reason of this reverse trend is that the former is affected by volcanic activity along the flow path, while the latter is not affected, as it is the discharge area of local groundwater flow system in the flank.