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Journal Articles

Paleohydrogeology of the Horonobe area, Northern Hokkaido, Japan; Groundwater flow conditions during glacial and postglacial periods estimated from chemical and isotopic data for fracture and pore water

Mochizuki, Akihito; Ishii, Eiichi

Applied Geochemistry, 155, p.105737_1 - 105737_15, 2023/08

 Times Cited Count:0 Percentile:0.01

Understanding the difference in groundwater flow between glacial and interglacial periods is crucial for predicting the impact of future climate changes on groundwater movement. This study assesses the difference in groundwater flow between the last glacial period (LGP) and the postglacial period (PGP) in fractured mudstones of the Horonobe area, Japan, by combining the data for stable isotopes ($$delta$$D and $$delta$$$$^{18}$$O) and Cl$$^{-}$$ concentration of fracture and pore waters with radiocarbon ($$^{14}$$C) age. The isotopic compositions of fractures and pore waters indicate that groundwater at 28$$sim$$250 m deep in a borehole closest to the recharge area comprises meteoric water, recharged under the same climates as the present. The fracture water has isotopic compositions more similar to meteoric water than the matrix pore water near the fracture. The $$^{14}$$C age of fracture water suggests meteoric water recharge during the PGP. At greater depths in the borehole and sampling points in other boreholes, the isotopic compositions indicate the mixing of glacial meteoric and altered connate water, with the fracture water having comparable isotopic compositions with the matrix pore water. The recharge timing of meteoric water is inferred to be the LGP or before based on $$^{14}$$C dating. These results suggest that the meteoric water recharged during the PGP flows at a shallow depth, whereas the meteoric water recharged during the LGP intruded to greater depths. This result is consistent with previous inferences from surface geophysical and geological surveys that the depths of local valleys during the LGP were greater by $$<$$50 m than the present ones and enhanced the downward hydraulic gradient. Combining the chemical and isotopic compositions of groundwater with $$^{14}$$C age helps assess the groundwater flow during the LGP and PGP in fractured rocks.

Journal Articles

Discrimination of the current level of activity of groundwater flow in deep underground by using stable water isotopes

Mochizuki, Akihito; Ishii, Eiichi

Isotope News, (784), p.23 - 27, 2022/12

no abstracts in English

Journal Articles

Numerical reproduction of the seasonal variation in dissolved uranium in Lake Biwa

Saito, Tatsuo; Yamazawa, Hiromi*; Mochizuki, Akihito

Journal of Environmental Radioactivity, 255, p.107035_1 - 107035_14, 2022/12

 Times Cited Count:0 Percentile:0(Environmental Sciences)

The seasonal variation of dissolved U (DU) in Lake Biwa was reproduced by the following model and parameter research. The introduced models are the water-DU mass balance, and the ion exchange between UO$$_{2}$$$$^{2+}$$ and H$$^{+}$$ on the lakeshore soil. The optimized parameters were the CEC of the lakeshore, TU as the sum of DU and AU (soil adsorbed U), kads and kdes as the first order reaction rate coefficients during rapid soil adsorption and desorption of U, respectively. Tabulated by the chemical equilibria constituting DU and analyzed the contribution of each chemical species, it is shown that the seasonal variation of DU is caused by the seasonal variation of pH. A correction to the ion-exchange equilibrium to shift to first order rate reaction only when the daily AU ratio increased above kads or decreased below kdes, improved the reproducibility of DU measurements and reproduced the delay of the DU peak from the pH peak.

JAEA Reports

Records of physicochemical parameters by geochemical monitoring system in the Horonobe Underground Research Laboratory (FY2020)

Dei, Shuntaro; Mochizuki, Akihito

JAEA-Data/Code 2022-001, 29 Pages, 2022/06

JAEA-Data-Code-2022-001.pdf:3.03MB
JAEA-Data-Code-2022-001-appendix(CD-ROM).zip:2.06MB

Japan Atomic Energy Agency had been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. In the Horonobe underground research project for FY 2020 and subsequent years, the pressure and water quality of groundwater have been continuously monitored using monitoring systems in order to obtain the data necessary for conducting the remaining important issues which were deduced from summarization of important issues between 2015-2019. This report presents pressure and physicochemical parameters (temperature, pH, electrical conductivity, oxidation-reduction potential and dissolved oxygen concentration) of groundwater which have been obtained from April 2020 to the end of March 2021 by the monitoring systems installed at the 140 m, 250 m and 350 m gallery.

Journal Articles

Assessment of the level of activity of advective transport through fractures and faults in marine deposits by comparison between stable isotope compositions of fracture and pore waters

Mochizuki, Akihito; Ishii, Eiichi

Hydrogeology Journal, 30(3), p.813 - 827, 2022/05

 Times Cited Count:3 Percentile:63.67(Geosciences, Multidisciplinary)

Assessment of the level of activity of advective transport through faults and fractures is essential for guiding the geological disposal of radioactive waste. In this study, the advective flow (active, inactive) of meteoric water through fractures is assessed by comparing stable isotopes ($$delta$$D and $$delta$$$$^{18}$$O) between fracture and pore waters obtained from four boreholes in marine deposits in the Horonobe area, Japan. At 27-83-m depth in one borehole and 28-250 m in another, the isotopic compositions of pore and fracture water reflect mixing with meteoric water, with stronger meteoric-water signatures being observed in the fracture water than in pore water of the rock matrix. At greater depths in these boreholes and at all sampling depths in the other two studied boreholes, the isotopic compositions of fracture and pore waters are comparable. These results suggest that the advective flow of meteoric water is active at shallow depths where fossil seawater is highly diluted in the two boreholes. This interpretation is compatible with the occurrence of present or paleo meteoric waters and tritium, whereby present meteoric water and tritium are limited to those depths in the two boreholes. This difference in the level of activity of advective flow is probably because of the glacial-interglacial difference in hydraulic gradients resulting from sea-level change. Although fractures are hydraulically connected to the surface through the sedimentary rock, advective flow through them is inferred to remain inactive so long as sea level does not fall substantially.

JAEA Reports

Records of physicochemical parameters by geochemical monitoring system in the Horonobe Underground Research Laboratory (FY2017-FY2019)

Dei, Shuntaro; Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi

JAEA-Data/Code 2021-005, 54 Pages, 2021/06

JAEA-Data-Code-2021-005.pdf:4.95MB
JAEA-Data-Code-2021-005-appendix(CD-ROM).zip:5.42MB

Japan Atomic Energy Agency had been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Groundwater pressure, pH, and oxidation-reduction potential in the deep groundwater have been continuously monitored with monitoring systems which were developed in the Horonobe URL Project. This report presents the physicochemical parameters of groundwater which have been obtained by the monitoring systems installed at the 140 m, 250 m and 350 m gallery. The data acquired from April 2017 to the end of March 2020 was summarized along with related information such as the specifications of boreholes.

Journal Articles

Proper methods for treatment and handling of real samples; Inland water

Mochizuki, Akihito

Bunseki, 2021(1), p.2 - 7, 2021/01

no abstracts in English

Journal Articles

Characterization of dissolved organic matter in deep groundwater by simple analytical methods applicable for small sample volumes

Mochizuki, Akihito; Sasamoto, Hiroshi; Bamba, Daiya*; Ikigaki, Kayoko*

Rikusuigaku Zasshi, 81(2), p.153 - 166, 2020/05

Characterization of humic substances in groundwater are usually carried out using isolated humic substances from large volume of groundwater. However, the isolation process expends much time and effect, and such method is not available if the volume of groundwater collected is small. In this study, convenient characterization methods available to small volume of samples (3D-fluorescense analysis, Gel permeation chromatography and ion chromatography) were applied to groundwater and surface water in the Horonobe area, Hokkaido, to characterize dissolved organic matter (DOM) including humic substances. 3D-fluorescense spectrum obtained from small volume of groundwater was similar to those from isolated humic substances, and showed little variation with depth. However, the peak position of spectrum for surface water was different from those for groundwater. Gel permeation chromatography showed that DOM in groundwater mainly consists of humic substances with molecule weight of approximately 1,200$$sim$$2,000 Da, and that the molecule weight decreases with depth. These results were consistent with the characteristics of isolated humic substances. Ion chromatography revealed that low molecule weight organic matter was minor component of DOM in the groundwater, which was consistent with the result of gel permeation chromatography. These results indicate that the methods applied in this study are useful for convenient characterization of DOM in groundwater.

JAEA Reports

Synthesis report on the R&D for the Horonobe Underground Research Laboratory; Project carried out during fiscal years 2015-2019

Nakayama, Masashi; Saiga, Atsushi; Kimura, Shun; Mochizuki, Akihito; Aoyagi, Kazuhei; Ono, Hirokazu; Miyakawa, Kazuya; Takeda, Masaki; Hayano, Akira; Matsuoka, Toshiyuki; et al.

JAEA-Research 2019-013, 276 Pages, 2020/03

JAEA-Research-2019-013.pdf:18.72MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies for geological disposal of High-level Radioactive Waste through investigations of the deep geological environment within the host sedimentary rock at Horonobe Town in Hokkaido, north Japan. The investigations will be conducted in three phases, namely "Phase 1: Surface based investigations", "Phase 2: Construction phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). According to the research plan described in the 3rd Mid- and Long- term Plan of JAEA, "Near-field performance study", "Demonstration of repository design option", and "Verification of crustal-movement buffering capacity of sedimentary rocks" are important issues of the Horonobe URL Project, and schedule of future research and backfill plans of the project will be decided by the end of 2019 Fiscal Year. The present report summarizes the research and development activities of these 3 important issues carried out during 3rd Medium to Long-term Research Phase.

JAEA Reports

Data of groundwater chemistry obtained in the Horonobe Underground Research Laboratory Project (FY2017-FY2019)

Miyakawa, Kazuya; Mezawa, Tetsuya*; Mochizuki, Akihito; Sasamoto, Hiroshi

JAEA-Data/Code 2020-001, 41 Pages, 2020/03

JAEA-Data-Code-2020-001.pdf:3.75MB
JAEA-Data-Code-2020-001-appendix(CD-ROM).zip:0.34MB

Development of technologies to investigate properties of deep geological environment and model development of geological environment have been pursued in "Geoscientific Research" in the Horonobe Underground Research Laboratory (Horonobe URL) project. A geochemical model which is a part of geological environment model requires the data of groundwater chemistry around the Horonobe URL for the development. This report summarizes the data obtained for 3 years from the fiscal year 2017 to 2019, especially for the results for measurement of physico-chemical parameters and analysis of groundwater chemistry, in the Horonobe URL project.

Journal Articles

Mudstone redox conditions at the Horonobe Underground Research Laboratory, Hokkaido, Japan; Effects of drift excavation

Mochizuki, Akihito; Ishii, Eiichi; Miyakawa, Kazuya; Sasamoto, Hiroshi

Engineering Geology, 267, p.105496_1 - 105496_11, 2020/03

 Times Cited Count:4 Percentile:27.35(Engineering, Geological)

The mechanical and hydraulic properties of rocks around mine drifts change significantly during the construction and operation of a radioactive-waste repository, with air intrusion causing the oxidation of rock and groundwater in excavation-damaged zones (EDZ). Redox conditions in such zones associated with niches excavated in mudstone at the Horonobe Underground Research Laboratory (URL), which is believed to be generally representative of conditions that could exist in the EDZ of a repository, were studied with the aim of improving our understanding of factors that control redox conditions in such rock-groundwater systems. Groundwater Eh values around the niches have reducing values of less than -150 mV. The SO$$_{4}$$$$^{2-}$$ concentration, regarded as an oxidation indicator, is consistently as low as 1 $$mu$$mol L$$^{-1}$$. Gas occupies more than 50% of zone volumes, including CH$$_{4}$$ and CO$$_{2}$$ with traces of N$$_{2}$$ and O$$_{2}$$. Cores drilled from host rock around a URL gallery were analyzed, with no pyrite dissolution or precipitation of calcium sulfates being found. It is concluded that oxidizing conditions do not exist in the excavation-damaged zones, which is attributed to the suppression of air intrusion by the release of CH$$_{4}$$ and CO$$_{2}$$ from groundwater as pressures decreased and their accumulation in fractures. The modeling of oxygen diffusion into host rock further indicates that a reducing environment is maintained around the URL drifts.

JAEA Reports

Groundwater pressure records by geochemical monitoring system in the 350 m gallery of the Horonobe Underground Research Laboratory (FY 2016-2018)

Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi

JAEA-Data/Code 2019-014, 56 Pages, 2020/02

JAEA-Data-Code-2019-014.pdf:6.56MB
JAEA-Data-Code-2019-014-appendix(CD-ROM).zip:5.81MB

Japan Atomic Energy Agency (JAEA) has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Groundwater pressure and geochemical parameters such as pH and oxidation-reduction potential in the deep groundwater have been continuously monitored with monitoring systems which were developed in the Horonobe URL Project. This report presents the data of groundwater pressure which have been obtained by the monitoring systems installed at the 350 m gallery. The data obtained from April 1, 2016 until March 31, 2019 was summarized along with related information such as the specifications of boreholes and the excavation of the URL.

Journal Articles

Remarks on accepting young best presentation award for the meeting of Japanese association of groundwater hydrology

Mochizuki, Akihito

Chikasui Gakkai-Shi, 61(4), P. 346, 2019/11

no abstracts in English

Journal Articles

Evaluation of uncertainty of redox potential in deep groundwater; A Case study in the Horonobe area, Hokkaido

Mochizuki, Akihito; Sasamoto, Hiroshi; Mezawa, Tetsuya*; Miyakawa, Kazuya

Chikasui Gakkai-Shi, 61(1), p.3 - 20, 2019/02

Redox potential of deep groundwater in the Horonobe area, Hokkaido, was measured, and uncertainty of the measurement and thermodynamic interpretation was evaluated. The redox potential of groundwater obtained using monitoring units in the Underground Research Laboratory ranged between -250 and -100 mV, and the effect of the excavation of drifts on the redox potential is considered to be small in spite of its temporal variation. The redox potential is controlled by the reaction of chemical pairs of SO$$_{4}$$$$^{2-}$$/FeS$$_{2}$$, SO$$_{4}$$$$^{2-}$$/HS$$^{-}$$ and CO$$_{2}$$(aq)/CH$$_{4}$$(aq). The comparison between the equilibrium potential for these reactions and the measured redox potentials suggests that $$pm$$50 mV of uncertainty for the measurement of the redox potential is appropriate.

Journal Articles

JAEA Reports

Records of physico-chemical parameters by geochemical monitoring system in the Horonobe Underground Research Laboratory

Mezawa, Tetsuya; Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi

JAEA-Data/Code 2018-001, 55 Pages, 2018/03

JAEA-Data-Code-2018-001.pdf:10.63MB
JAEA-Data-Code-2018-001-appendix(CD-ROM).zip:8.57MB

Japan Atomic Energy Agency has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Geochemical parameters of groundwater pressure, pH, and oxidation-reduction potential in the deep groundwater has been continuously monitored with monitoring systems which were developed in the Horonobe URL Project. This report presents the physico-chemical parameters of groundwater which have been obtained by the monitoring systems installed at the 140 m, 250 m and 350 m gallery. The data obtained until March 31, 2017 was summarized along with related information such as the specifications of boreholes and the excavation of the URL.

JAEA Reports

Data of groundwater chemistry obtained in the Horonobe Underground Research Laboratory Project (FY2014-2016)

Miyakawa, Kazuya; Mezawa, Tetsuya; Mochizuki, Akihito; Sasamoto, Hiroshi

JAEA-Data/Code 2017-012, 60 Pages, 2017/10

JAEA-Data-Code-2017-012.pdf:7.94MB
JAEA-Data-Code-2017-012-appendix(CD-ROM).zip:0.09MB

Development of technologies to investigate properties of deep geological environment and model development of geological environment have been pursued in "Geoscientific Research" in the Horonobe Underground Research Laboratory (Horonobe URL) project. A geochemical model which is a part of geological environment model requires the data of groundwater chemistry around the Horonobe URL for the development. This report summarizes the data obtained for 3 years from the fiscal year 2014 to 2016, especially for the results for measurement of physico-chemical parameters and analysis of groundwater chemistry, in the Horonobe URL project.

JAEA Reports

Groundwater pressure records by geochemical monitoring system in the Horonobe Underground Research Laboratory

Mezawa, Tetsuya; Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi

JAEA-Data/Code 2017-010, 63 Pages, 2017/06

JAEA-Data-Code-2017-010.pdf:9.66MB
JAEA-Data-Code-2017-010-appendix(CD-ROM).zip:5.08MB

Japan Atomic Energy Agency (JAEA) has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Geochemical parameters of groundwater pressure, pH, and oxidation-reduction potential in the deep groundwater has been continuously monitored by the monitoring system which was developed in the Horonobe URL Project. This report presents the data of groundwater pressure which have been obtained by the monitoring system installed at the 140 m and 350 m gallery. The data obtained until March 31, 2016 was summarized along with related information such as the specifications of boreholes and the excavation of the URL.

Oral presentation

The Redox condition of rocks in the excavation damaged zone of galleries in the Horonobe Underground Research Laboratory

Mochizuki, Akihito; Miyakawa, Kazuya; Ishii, Eiichi; Sasamoto, Hiroshi; Sato, Toshinori

no journal, , 

no abstracts in English

Oral presentation

A Case study for evaluation of uncertainty of redox potential in deep groundwater

Mochizuki, Akihito; Sasamoto, Hiroshi; Mezawa, Tetsuya*; Miyakawa, Kazuya

no journal, , 

Redox potential of deep groundwater in the Horonobe area, Hokkaido, was measured, and uncertainty of the measurement and thermodynamic interpretation was evaluated. The redox potential of groundwater ranged between -250 and -100 mV, and the effect of the excavation of drifts on the redox potential is considered to be small in spite of its temporal variation. The redox potential is controlled by the reaction of chemical pairs of SO$$_{4}$$$$^{2-}$$/FeS$$_{2}$$, SO$$_{4}$$$$^{2-}$$/HS$$^{-}$$ and CO$$_{2}$$(aq)/CH$$_{4}$$(aq). The comparison between the equilibrium potential for these reactions and the measured redox potentials suggests that $$pm$$50 mV of uncertainty for the measurement of the redox potential is appropriate.

34 (Records 1-20 displayed on this page)