11:00 AM - 11:15 AM
[HCG20-02] Deep groundwater mobility at costal area evaluated by groundwater dating
Keywords:groundwater dating, modern seawater, fossil seawater, isotope, noble gas
On high-level radioactive waste disposal and CO2 storage in geological formation, costal area is the favorable from transportation point of view. and groundwater flow in deep costal area attracts great attention. Groundwater dating methods using isotope and noble gases are one of the most promising methods to evaluate groundwater. Thus, groundwater dating methods using drilling core and pumping groundwater have been conducted to deep borehole in costal area.
On 1200 m deep borehole in Horonobe, Hokkaido, modern meteoric water, glacial meteoric water and fossil seawater were confirmed in the sand and silt layer at depths of 300-360 m, the silt layer at 90-300 m, and the silt mud layer below 800 m, respectively.
On 500 m deep borehole in Yokosuka, Kanagawa, brackish water mixed with modern meteoric water and modern seawater, and fossil seawater were confirmed in the sand and silt layer at depths of 0-200 m, the clay layer below 200 m, respectively.
For identification on modern meteoric water and modern seawater, 14C, 4He, δD and δ18O are useful. The typical modern meteoric water and modern seawater are detectable 14C concentration, low 4He concentration (not accumulated), δD and δ18O ratios plotted on mixing line between modern meteoric water and modern seater. For identification on fossil seawater, 36Cl, 4He, δD and δ18O are useful. The fossil seawater has high 36Cl/Cl ration compared to modern seawater, high 4He concentration (accumulated), alteredδD and δ18O ratio due to water rock interaction.
The groundwater dating methods are useful to understand groundwater mobility, especially, identifying modern and fossil seawater.
A part of this work was supported by the Ministry of Economy, Trade, and Industry (METI) under the R&D support program entitled “Development of enhancing the disposal system in the coastal region” .
On 1200 m deep borehole in Horonobe, Hokkaido, modern meteoric water, glacial meteoric water and fossil seawater were confirmed in the sand and silt layer at depths of 300-360 m, the silt layer at 90-300 m, and the silt mud layer below 800 m, respectively.
On 500 m deep borehole in Yokosuka, Kanagawa, brackish water mixed with modern meteoric water and modern seawater, and fossil seawater were confirmed in the sand and silt layer at depths of 0-200 m, the clay layer below 200 m, respectively.
For identification on modern meteoric water and modern seawater, 14C, 4He, δD and δ18O are useful. The typical modern meteoric water and modern seawater are detectable 14C concentration, low 4He concentration (not accumulated), δD and δ18O ratios plotted on mixing line between modern meteoric water and modern seater. For identification on fossil seawater, 36Cl, 4He, δD and δ18O are useful. The fossil seawater has high 36Cl/Cl ration compared to modern seawater, high 4He concentration (accumulated), alteredδD and δ18O ratio due to water rock interaction.
The groundwater dating methods are useful to understand groundwater mobility, especially, identifying modern and fossil seawater.
A part of this work was supported by the Ministry of Economy, Trade, and Industry (METI) under the R&D support program entitled “Development of enhancing the disposal system in the coastal region” .