5:15 PM - 7:15 PM
[AHW31-P08] Study on the groundwater flow system of Namie, Fukushima – 2. Water quality characteristics of unconfined groundwater and geological structure at coastal and inland area.
Keywords:Namie Town, groundwater, water quality, geological structure, δ18O and δ2H, 87Sr/86Sr ratio
Namie Town, located at coastal region (Hama-dori) of Fukushima Prefecture, was serious damaged by the 2011 off the Pacific coast of Tohoku Earthquake. Especially, the influence of radioactive materials released to the environment due to the nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) was severe. Almost all of the Namie town had been specified to the evacuation zone after FDNPP accident; however, recently the specification is lifting near the coastal area.
The source of public water at Namie Town is shallow (unconfined) groundwater, and this groundwater was also used for domestic water and agricultural water. In order to use the groundwater for sustainability, it is important to understand the groundwater flow system and groundwater storage. Unfortunately, little research has been done on the detailed groundwater flow at Namie Town; therefore, the objectives of this study are to understand the groundwater quality, groundwater storage, water residence time, and groundwater flow system at Namie Town. In this presentation, we will report the results of investigation regarding to the water quality of domestic wells and observation well at coastal and inland area.
The observation has been started at one well of coastal area since December in 2022, and at four wells of inland area since December in 2023. The depth of these wells is less than 10 m deep, and they are unconfined groundwater. The observation well was installed at inland area, located at approximately 7.3 km from the coast, at January in 2025. The well depth is 12 m deep, and well strainer was installed from 2 to 11 m deep. The EC, pH, water temperature, ORP and water table were measured on site, and groundwater were sampled by water sampler. Regarding the chemical analysis, dissolved inorganic ions, trace elements, stable isotopes of oxygen and hydrogen, and 87Sr/86Sr ratio were analyzed by the IC (ICS-6000), ICP-MS (Agilent 7500cx), WS-CRDS analyzers (Picarro L2140-i), and MC-ICP-MS (Neptune Plus), respectively.
The groundwater quality of coastal area was Ca-HCO3, concentration of dissolved ions, Fe and Al concentration was relatively high; however, no seawater intrusion has been detected. The concentration of dissolved ions of this groundwater has changed since August in 2024, it may be affected by the land improvement. The groundwater quality of inland area was Ca-HCO3 or (Na+Ca)-HCO3, and concentration of dissolved ions was relatively low and showed a tendency to varied in each site. The nitrate concentration of one well was higher than that of other wells (approximately 22 mg/L), it may be affected by the farming. In case of the observation well, water quality was Ca-HCO3 and concentration of dissolved ions was relatively high. And concentration of manganese and zinc was also relatively high. Sr isotope ratios (87Sr/86Sr) of each well water were reflected the geological difference. In addition, δ18O and δ2H showed the negative correlation with altitude. In future, we will attempt the estimation of groundwater recharge area by using stable isotopes of oxygen, hydrogen, and strontium.
The source of public water at Namie Town is shallow (unconfined) groundwater, and this groundwater was also used for domestic water and agricultural water. In order to use the groundwater for sustainability, it is important to understand the groundwater flow system and groundwater storage. Unfortunately, little research has been done on the detailed groundwater flow at Namie Town; therefore, the objectives of this study are to understand the groundwater quality, groundwater storage, water residence time, and groundwater flow system at Namie Town. In this presentation, we will report the results of investigation regarding to the water quality of domestic wells and observation well at coastal and inland area.
The observation has been started at one well of coastal area since December in 2022, and at four wells of inland area since December in 2023. The depth of these wells is less than 10 m deep, and they are unconfined groundwater. The observation well was installed at inland area, located at approximately 7.3 km from the coast, at January in 2025. The well depth is 12 m deep, and well strainer was installed from 2 to 11 m deep. The EC, pH, water temperature, ORP and water table were measured on site, and groundwater were sampled by water sampler. Regarding the chemical analysis, dissolved inorganic ions, trace elements, stable isotopes of oxygen and hydrogen, and 87Sr/86Sr ratio were analyzed by the IC (ICS-6000), ICP-MS (Agilent 7500cx), WS-CRDS analyzers (Picarro L2140-i), and MC-ICP-MS (Neptune Plus), respectively.
The groundwater quality of coastal area was Ca-HCO3, concentration of dissolved ions, Fe and Al concentration was relatively high; however, no seawater intrusion has been detected. The concentration of dissolved ions of this groundwater has changed since August in 2024, it may be affected by the land improvement. The groundwater quality of inland area was Ca-HCO3 or (Na+Ca)-HCO3, and concentration of dissolved ions was relatively low and showed a tendency to varied in each site. The nitrate concentration of one well was higher than that of other wells (approximately 22 mg/L), it may be affected by the farming. In case of the observation well, water quality was Ca-HCO3 and concentration of dissolved ions was relatively high. And concentration of manganese and zinc was also relatively high. Sr isotope ratios (87Sr/86Sr) of each well water were reflected the geological difference. In addition, δ18O and δ2H showed the negative correlation with altitude. In future, we will attempt the estimation of groundwater recharge area by using stable isotopes of oxygen, hydrogen, and strontium.