Journal of Groundwater Hydrology
Online ISSN : 2185-5943
Print ISSN : 0913-4182
ISSN-L : 0913-4182
ORIGINAL PAPER
Hydrogeochemistry of unconfined groundwater along the flowpaths on Musashino Uplands, Tokyo Metropolitan
Masaru YAMANAKAMingzhe ZHAO
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2024 Volume 66 Issue 2 Pages 103-122

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Abstract

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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© 2024 Japanese Association of Groundwater Hydrology
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