11:00 AM - 1:00 PM
[HTT18-P01] 87Sr/86Sr isotope ratios of groundwater, spring water and river water near the coastal area of Fukushima and estimation of groundwater recharge area using a multi-tracer
Keywords:coastal area of Fukushima prefecture, 87Sr/86Sr, recharge area, groundwater, river water, multi-tracer
Objectives
The tsunami, caused by the 2011 off the Pacific coast of Tohoku Earthquake, flooded large area near the coastal area from Kanto district to Tohoku district, and water salinization occurred in many wells at those areas. And also, groundwater pollution occurred in some areas due to radioactive materials caused by the Fukushima Daiichi Nuclear Power Station (FDNPP) accident. It is important to determine the water quality and groundwater flow system for sustainable groundwater use. The objectives of this study are to understand the characteristics of water quality, groundwater recharge area, and groundwater flow systems near the coastal area of Fukushima Prefecture.
Methodology
The observation has been started since April 2014 near the coastal area and Abukuma mountain area of Fukushima Prefecture, and the EC, pH, water temperature, ORP, water level, and discharge rate were measured in the field, and water for chemical analysis were sampled at each site. The dissolved inorganic ions, trace elements, δ18O, δ2H, and Sr isotope ratio (87Sr/86Sr) were analyzed for all samples, and CFCs and SF6 for estimating of water residence time were measured in some sites. 87Sr/86Sr values are different depend on the geological conditions. In this study area, the geological condition is different. A granitic rocks are deposited near the Abukuma mountains, and sedimentary rocks are deposited in the plateaus near the coast. 87Sr/86Sr values of water are likely different between a granitic rocks area and sedimentary rocks area; therefore, the groundwater recharge area can be estimated by the 87Sr/86Sr values.
In this presentation, we will focus on the characteristics and spatial distribution of 87Sr/86Sr values in water samples (groundwater, spring water, river water), and report estimation result of recharge area by using the multi-tracer method.
Results and discussion
87Sr/86Sr values of groundwater, spring water , river water were from 0.70545 to 0.71191, and that of hot spring water was high; however, 87Sr/86Sr value in other sites was almost below 0.70918 (=sea water value). 87Sr/86Sr values were divided tow groups; one is 87Sr/86Sr = from 0.708 to 0.709, and another is 87Sr/86Sr < 0.708. The former almost corresponded to artesian wells and deep wells (deep groundwater), and the latter almost corresponded to spring water and shallow wells (shallow groundwater). As a result of observation so far in this study, it was estimated that the deep groundwater and artesian well water were recharged in the inland area (Abukuma mountains) and shallow groundwater and spring water were recharged in the upland area near the coast. Because the granitic rocks were deposited in large area of the Abukuma mountains area, the 87Sr/86Sr values of water which was recharged at Abukuma mountain area is likely from 0.708 to 0.709. On the other hand, the sedimentary rocks were deposited in the plateaus near the coast; therefore, the 87Sr/86Sr values of water which was recharged at the plateaus is likely relatively low (approximately 0.708 or less). So, there is no contradiction between result of previously study and estimation results of 87Sr/86Sr values mentioned above.
In future study, we will understand the relation between water quality and Sr isotope ratios, and consider the groundwater flow systems using the multi-tracer including the 87Sr/86Sr values.
The tsunami, caused by the 2011 off the Pacific coast of Tohoku Earthquake, flooded large area near the coastal area from Kanto district to Tohoku district, and water salinization occurred in many wells at those areas. And also, groundwater pollution occurred in some areas due to radioactive materials caused by the Fukushima Daiichi Nuclear Power Station (FDNPP) accident. It is important to determine the water quality and groundwater flow system for sustainable groundwater use. The objectives of this study are to understand the characteristics of water quality, groundwater recharge area, and groundwater flow systems near the coastal area of Fukushima Prefecture.
Methodology
The observation has been started since April 2014 near the coastal area and Abukuma mountain area of Fukushima Prefecture, and the EC, pH, water temperature, ORP, water level, and discharge rate were measured in the field, and water for chemical analysis were sampled at each site. The dissolved inorganic ions, trace elements, δ18O, δ2H, and Sr isotope ratio (87Sr/86Sr) were analyzed for all samples, and CFCs and SF6 for estimating of water residence time were measured in some sites. 87Sr/86Sr values are different depend on the geological conditions. In this study area, the geological condition is different. A granitic rocks are deposited near the Abukuma mountains, and sedimentary rocks are deposited in the plateaus near the coast. 87Sr/86Sr values of water are likely different between a granitic rocks area and sedimentary rocks area; therefore, the groundwater recharge area can be estimated by the 87Sr/86Sr values.
In this presentation, we will focus on the characteristics and spatial distribution of 87Sr/86Sr values in water samples (groundwater, spring water, river water), and report estimation result of recharge area by using the multi-tracer method.
Results and discussion
87Sr/86Sr values of groundwater, spring water , river water were from 0.70545 to 0.71191, and that of hot spring water was high; however, 87Sr/86Sr value in other sites was almost below 0.70918 (=sea water value). 87Sr/86Sr values were divided tow groups; one is 87Sr/86Sr = from 0.708 to 0.709, and another is 87Sr/86Sr < 0.708. The former almost corresponded to artesian wells and deep wells (deep groundwater), and the latter almost corresponded to spring water and shallow wells (shallow groundwater). As a result of observation so far in this study, it was estimated that the deep groundwater and artesian well water were recharged in the inland area (Abukuma mountains) and shallow groundwater and spring water were recharged in the upland area near the coast. Because the granitic rocks were deposited in large area of the Abukuma mountains area, the 87Sr/86Sr values of water which was recharged at Abukuma mountain area is likely from 0.708 to 0.709. On the other hand, the sedimentary rocks were deposited in the plateaus near the coast; therefore, the 87Sr/86Sr values of water which was recharged at the plateaus is likely relatively low (approximately 0.708 or less). So, there is no contradiction between result of previously study and estimation results of 87Sr/86Sr values mentioned above.
In future study, we will understand the relation between water quality and Sr isotope ratios, and consider the groundwater flow systems using the multi-tracer including the 87Sr/86Sr values.