Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-HW Hydrology & Water Environment

[A-HW24] Isotope Hydrology 2019

Mon. May 27, 2019 10:45 AM - 12:15 PM 105 (1F)

convener:Masaya Yasuhara(Rissho Univ.), Kohei Kazahaya(Geological Survey of Japan, AIST), Shinji Ohsawa(Institute for Geothermal Sciences, Graduate School of Science, Kyoto University), Kazuyoshi Asai(Geo Science Laboratory), Chairperson:Noritoshi Morikawa(産業技術総合研究所活断層・火山研究部門), Kazuyoshi Asai(Geo-Science Laboratory), Kohei Kazahaya(Geological Survey of Japan, AIST)

11:45 AM - 12:00 PM

[AHW24-08] An isotopic study on shallow groundwater origins in a densely-populated area in Shinagawa, central Tokyo, Japan

*Masaya Yasuhara1, Akihiko Inamura2, Takashi Nakamura3, Kazuyoshi Asai4 (1.Rissho Univ., 2.Geological Survey of Japan, AIST, 3.Yamanashi Univ., 4.Geo Science Laboratory)

Keywords:Tokyo, shallow groundwater, origins of groundwater, water leakage, sewage leakage, isotope

Stable isotopes (δD and δ18O) and hydrochemical tracers (electric conductivity, NH4+, NO3-, Cl-) of water were applied to quantify 1) rainfall infiltration (natural recharge), 2) water supply leakage, and 3) sewage leakage in a shallow aquifer in a densely-populated area in Shinagawa, central Tokyo, Japan. Despite of a quite small area about 0.5 km (E-W) by 1 km (N-S), shallow groundwater took on a wide range of values: 28 ∼ 70 mS/m electric conductivity, 0.0 ∼ 9.1 mg/L NH4+, 0.1 ~ 36.2 mg/L NO3-, 4.8 ∼ 46.6 mg/L Cl-, and -8.7 ∼ -7.4‰ δ18O. A ternary mixing model was used based on the Cl-concentration and d18O of three plausible origins of groundwater to estimate fractions of each component in shallow groundwater in the study area. As a result, a fraction of sewage leakage in groundwater proved large for one well as much as 70%, while for some wells rainfall infiltration contributed more than 80% of water to the formation of groundwater. These remarkable differences in contribution of urban leakage to the shallow aquifer may result from the different state of the water infrastructure in the vicinity of the respective wells.