ボーリング孔での原位置地下水試料の採取法と留意点

抄録

Some technical notes on methodology of high quality in-situ deep groundwater sampling in drill holes are described. It is essential to know deep groundwater chemistry to make safety assessment of geological isolation of high level radioactive wastes. Chemistry of sampled groundwater can be changed by artificial disturbances such as drilling water contamination, mix with groundwater in different aquifers, reaction with atmosphere, and degassing by pressure leak. Because of low permeability of hard rocks in deeper formation, it is necessary to find water paths like open-space fractures to obtain groundwater in situ in realistic time periods. Water seepage records in drilling log, well loggings such as precise flowmeter log and flowing electric conductivity log, and drilled core observation are effective to recognize water paths. Attention should be paid for sampling immediately after drilling (if possible), removal of contaminated water from wells and adjacent formation, suppression of hydrogeochemical disturbance in and around wells, and maintenance of physicochemical conditions during sampling, withdrawal and transportation.