12:00 PM - 12:15 PM
[AHW26-05] Evaluation of groundwater flow system in the northern part of the Kamikita Plain, Aomori Prefecture, by drilling a borehole and survey of existing wells
Keywords:groundwater flow, Borehole drilling, Sedimentary Rock, Kamikita Plain, Stable Isotope, Groundwater Age
We have conducted a survey of domestic water wells distributed in the northern part of the Kamikita Plain (around Lake Ogawara) in Aomori Prefecture to investigate the characteristics of water chemistry, and then have constructed the groundwater flow regime. To verify the conceptual model, we conducted an excavation survey up to a depth of 200 m in the Kamikita Plain. Various kind of data were obtained for evaluation of groundwater flow system, i.e., chemical and isotope composition of groundwater and porewater extracted from core samples, depth profile of permeability, water level and precise temperature logging data.
The groundwaters of existing well in the western part of Lake Ogawara shows Ca-HCO3 to Na-HCO3 types and show a low hydrogen isotope ratio compared to the groundwater on the east and northwest sides of Lake Ogawara, which reflects the present recharged water value in this region. In addition, the 14C ages of the groundwater in the western part of Lake Ogawara all indicated the age corresponding to the last glacial period. However, since the well is pumped with strainers at multiple depths, the water chemistry and isotope ratio of the collected sample is the average value of groundwater obtained from these multiple depths. Therefore, the resolution in the depth progfile is ambiguous.
As a result of water sampling and pumping tests at six depths from excavated borehole, even in shallow areas (27.3-30.1m), a 14C age of about 10,000 years has been obtained. In addition, the chemical properties of groundwaters changed clearly from the shallow layer of Ca・Na・Mg-HCO3 type to Na・Ca・Mg-HCO3 type, and NaHCO3 type in the deepest part (190.7-201.4 m). The hydrogen isotope ratio is lower than the Shitionohe river water (-64 ‰ to -58 ‰), similar to the result of the existing well. The water level in the pumping test conducted at six depths tends to increase with the depth. Changes in water chemistry and water level mean that different aquifers are formed in these formations. The existence of groundwater recharged during the colder era inferred in the conceptual groundwater flow model was verified by our boring excavation. Moreover, we confirmed the existence of different ground water flow systems for each stratum both from groundwater chemistry and hydraulic data.
Acknowledgement: The main part of this research project has been conducted as the regulatory supporting research funded by the Secretariat of Nuclear Regulation Authority (NRA), Japan.
The groundwaters of existing well in the western part of Lake Ogawara shows Ca-HCO3 to Na-HCO3 types and show a low hydrogen isotope ratio compared to the groundwater on the east and northwest sides of Lake Ogawara, which reflects the present recharged water value in this region. In addition, the 14C ages of the groundwater in the western part of Lake Ogawara all indicated the age corresponding to the last glacial period. However, since the well is pumped with strainers at multiple depths, the water chemistry and isotope ratio of the collected sample is the average value of groundwater obtained from these multiple depths. Therefore, the resolution in the depth progfile is ambiguous.
As a result of water sampling and pumping tests at six depths from excavated borehole, even in shallow areas (27.3-30.1m), a 14C age of about 10,000 years has been obtained. In addition, the chemical properties of groundwaters changed clearly from the shallow layer of Ca・Na・Mg-HCO3 type to Na・Ca・Mg-HCO3 type, and NaHCO3 type in the deepest part (190.7-201.4 m). The hydrogen isotope ratio is lower than the Shitionohe river water (-64 ‰ to -58 ‰), similar to the result of the existing well. The water level in the pumping test conducted at six depths tends to increase with the depth. Changes in water chemistry and water level mean that different aquifers are formed in these formations. The existence of groundwater recharged during the colder era inferred in the conceptual groundwater flow model was verified by our boring excavation. Moreover, we confirmed the existence of different ground water flow systems for each stratum both from groundwater chemistry and hydraulic data.
Acknowledgement: The main part of this research project has been conducted as the regulatory supporting research funded by the Secretariat of Nuclear Regulation Authority (NRA), Japan.