5:15 PM - 6:45 PM
[HTT16-P01] Study on the groundwater flow system of Namie, Fukushima – Results of preliminary investigation and future research plan.
Keywords:Namie town, groundwater flow, water quality, δ18O, δ2H, 87Sr/86Sr ratio
Namie town, which is located 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. In these areas, the residents are returning and agricultural and manufacturing activity are restarting. The source of public water at Namie town is shallow groundwater, and groundwater was also used for domestic water and agricultural water; therefore, the groundwater use is likely to increase in the future. In order to use the groundwater for sustainability, it is important to understand the groundwater flow system and groundwater storage. Unfortunately, there was almost not the observation regarding to 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 preliminary investigation regarding to the domestic wells at coastal and inland area at Namie town.
The groundwater samples have been sampled at 1 well of coastal area since December in 2022 and at 2 wells of inland area since December in 2023. The depth of these wells is approximately 3-4 m. And these wells are unconfined aquifer because the low-permeable layer is lain at the depth of 15-20 m deep. The 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), CRDS (Picarro L2140-i), and MC-ICP-MS (Neptune Plus), respectively.
The groundwater quality of well located at the coastal area was Ca-HCO3, and dissolved concentration was relatively high. And the nitrate concentration increased at summer period, it may be affected by the agricultural activity. The groundwater quality of wells located at inland area was Ca-HCO3 and Na-HCO3, and dissolved concentration was relatively low; however, the nitrate concentration of one well was higher than other wells (approximately 22 mg/L), it may be affected by the farming. The stable isotopes of oxygen and hydrogen of groundwater indicated the negative correlation with the altitude of each well. In the future, we will estimate the groundwater recharge area with using these isotope data. As a result of continuous observation every 30 minutes, the water table of coastal area was from GL –3.073 to –2.662 m (equivalent to from +0.127 to +0.538 m above sea level) and almost constant. The water temperature indicate from 11.5 to 12.5 °C, it almost corresponded to the annual mean air temperature at Namie. The EC value was almost constant. In addition, as a result of water table measurements of three sites measured at December in 2023, it was understood that the unconfined groundwater flowed from west to east.
In the future, the observation wells, which is correspond to the unconfined and confined aquifer, will be installed at three sites due to understand the detail groundwater flow systems.
The groundwater samples have been sampled at 1 well of coastal area since December in 2022 and at 2 wells of inland area since December in 2023. The depth of these wells is approximately 3-4 m. And these wells are unconfined aquifer because the low-permeable layer is lain at the depth of 15-20 m deep. The 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), CRDS (Picarro L2140-i), and MC-ICP-MS (Neptune Plus), respectively.
The groundwater quality of well located at the coastal area was Ca-HCO3, and dissolved concentration was relatively high. And the nitrate concentration increased at summer period, it may be affected by the agricultural activity. The groundwater quality of wells located at inland area was Ca-HCO3 and Na-HCO3, and dissolved concentration was relatively low; however, the nitrate concentration of one well was higher than other wells (approximately 22 mg/L), it may be affected by the farming. The stable isotopes of oxygen and hydrogen of groundwater indicated the negative correlation with the altitude of each well. In the future, we will estimate the groundwater recharge area with using these isotope data. As a result of continuous observation every 30 minutes, the water table of coastal area was from GL –3.073 to –2.662 m (equivalent to from +0.127 to +0.538 m above sea level) and almost constant. The water temperature indicate from 11.5 to 12.5 °C, it almost corresponded to the annual mean air temperature at Namie. The EC value was almost constant. In addition, as a result of water table measurements of three sites measured at December in 2023, it was understood that the unconfined groundwater flowed from west to east.
In the future, the observation wells, which is correspond to the unconfined and confined aquifer, will be installed at three sites due to understand the detail groundwater flow systems.