Journal of Groundwater Hydrology
Online ISSN : 2185-5943
Print ISSN : 0913-4182
ISSN-L : 0913-4182
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Displaying 1-5 of 5 articles from this issue
ORIGINAL PAPER
  • Yasuharu TANAKA, Kazuyuki GOTO, Toshiaki UDA, Shintaro NOHARA
    2024 Volume 66 Issue 2 Pages 85-101
    Published: May 31, 2024
    Released on J-STAGE: June 22, 2024
    JOURNAL FREE ACCESS

    In-situ tracer experiment is considered an effective means of understanding the migration characteristics of groundwater solutes under actual underground environments. The authors have developed tracer test equipment applicable to mainly fractured rock masses, and methods for evaluating experimental results. To confirm their usefulness, a tracer experiment was conducted for a single fracture in a granitic rock mass at the Mizunami Underground Research Laboratory. A numerical analysis was performed for the breakthrough curves obtained from the experiment. As a result, we were able to estimate the solute transport characteristics of the target fracture, including the aperture, the dispersion length, and the sorption coefficients of the sorbing tracers on the fracture surface and the rock matrix. Batch sorption tests were also conducted for rock samples collected at the test site.

    The differences between the sorption coefficients estimated from in-situ tracer tests and those obtained from batch tests were shown for Toki granite.

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  • Masaru YAMANAKA, Mingzhe ZHAO
    2024 Volume 66 Issue 2 Pages 103-122
    Published: May 31, 2024
    Released on J-STAGE: June 22, 2024
    JOURNAL FREE ACCESS

    It is investigated to identify the controlling processes for chemical compositions of unconfined groundwater along mainly eastward flowpaths on Musashino Uplands, located in Tokyo Metro politan. Along the flowpaths, Ca2+ concentrations decreased, while Mg2+ and Na concentrations increased. Considering the facts that the observed changes along the paths occurred without a remarkable increase of TDS (total dissolved solid) values and that saturation index for calcite (SIc) of the groundwater samples indicated they were mostly under unsaturated conditions, the changes would be attributed to cation exchange reactions. This idea is concordant well with two previsous reports; one is for exchangeable cation compositions extracted from Kanto Loam and the other is for long-term monitoring of groundwater chemical compositions. Moreover, decrease of NO3 concentrations and increase of SO4 2- concentrations occured in special wards, the eastern part of Tokyo, These occurences

    can be caused by denitrification under anoxic conditions associated with higher covering area and by oxidation of sulfide involved in marine clays. Such an oxidation is likely induced by local percolation of precipitation and/or leakage from water supply pipes accompanied with dissolved O2. By using previ ous reports for the unconfined groundwater sources and aquifer parameters in Musashino Uplands, it is

    evaluated that percentage of the both of leakage and precipitation components is approximately 16% and

    the remaining is for groundwater advection component from upstream of special wards. In this evalua tion, such a low percentage of oxic water components is accordant with regards to the occurrence capa bility for anoxic conditions in special wards.

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