Clogging mechanism of injection wells is clarified from monitoring data of flow rate and hydraulic head at three sites of open-loop ground source heat pump systems in Gifu, Yokkaichi and Nagoya. (Δh_max / Q_max) / (V / S) becomes larger, when hydraulic conductivity of aquifers is smaller, or injected water is more oxidized where Δh_max is change of drawup (m) at maximum flow rate Q_max (m ³ /s) due to clogging, V is accumulated injection volume (m ³ ), S is surface area of well screen (m ² ). The relationship of flow rate Q (m ³ /s) and drawup h (m) exhibits the increase of the well loss coefficient C in summer and the aquifer loss coefficient B in winter. This suggests that iron-oxidizing bacteria is more active due to the higher injection temperature in summer and less in winter.

Rishiri Island, known for having one of the largest submarine springs in Japan, is a volcanic island located in Hokkaido. We applied multi-transient tracers (³H, CFCs, and SF₆) to estimate the residence times of the submarine and terrestrial springs on Rishiri Island. All of the springs contained ³H higher than natural ³H level, indicating that the groundwater on Rishiri Island was primarily recharged during post-bomb periods. CFCs and SF₆ concentrations were relatively high in the terrestrial springs and north-eastern submarine spring, and low in the south-western submarine spring. Tracer plots between the ³H, CFCs, and SF₆ suggested that the flow pattern of the groundwater on Rishiri Island can be approximated via two flow models: an exponential mixing model (EMM) and a piston flow model (PFM). The terrestrial springs and the north-east submarine spring are formed via a mixture of groundwater with different recharge ages, and the average transit time based on the EMM was approximately 10 to 45 years. The large-scale submarine spring in the south-west may be formed via piston-like groundwater flow at the bottom of a buried valley, and its transit time is estimated to be 40 years. The residence time of spring water was positively correlated with recharge elevation, suggesting that the scale of the groundwater flow system is larger for submarine springs than for terrestrial springs.