11:00 AM - 11:15 AM
[AHW24-02] Empirical study on shallow groundwater system in the coastal lowlands of Shinagawa Ward, Tokyo
Keywords:Tokyo Bay coastal lowlands, Urban area, Shallow groundwater, Isotopes, Sewage leakage
A study is underway to elucidate and typify the groundwater system in urban shallow groundwater. In this presentation, shallow groundwater chemistry and its origin in the Kita-Shinagawa and Minami-Shinagawa areas of Shinagawa Ward in the Tokyo Bay Lowland will be discussed and compared.
Field surveys and water sampling were conducted in August 2021 (Kita-shinagawa area) and September 2023 (Minami-shinagawa are) for 8 wells (depths shallower than 12 m) in the Kita-shinagawa area and 15 wells (depths shallower than 11 m) in the Minami-shinagawa area. The geology of the two areas is similar, ranging mainly from gravel to silty sand, but the age of the public sewage system differs by up to 10 years between the two areas (1960s in the Kita-shinagawa area and 1970s in the Minami-shinagawa area). Water chemistry results showed that chloride ion ranged from 11.4 to 38.3 mg/L (Kita-Shinagawa area) and from 4.0 to 28.0 mg/L (Minami-Shinagawa area), nitrate ion from n.d. (not detected) to 22.4 mg/L (Kita-Shinagawa area) and from 7.2 to 38.1 mg/L (Minami-Shinagawa area), sulfate ion from 10.6 to 40.4 mg/L (Kita-Shinagawa area) and from 7.3 to 34.6 mg/L (Minami-Shinagawa area). The contribution of precipitation, water leakage and sewage leakage to groundwater recharge in the two areas was calculated using a three-component mixture analysis based on chloride ion concentrations and stable isotope ratios of water oxygen. The contribution of sewage leakage tended to be higher in the groundwater of the Kita-shinagawa area. The nitrogen stable isotope ratio of nitrate and sulfur stable isotope ratio of sulfate indicate that the groundwater in the Kita-shinagawa area is more reductive than that in the Minami-shinagawa area, and that denitrification and sulfate reduction reactions are ongoing in the groundwater in the Kita-shinagawa area. This suggests that the difference in the age of the public sewers in the two areas, namely the difference in the degree of aging of the public sewers, is the main cause of the distinct differences in groundwater quality and origin in the two areas, as described above.
Field surveys and water sampling were conducted in August 2021 (Kita-shinagawa area) and September 2023 (Minami-shinagawa are) for 8 wells (depths shallower than 12 m) in the Kita-shinagawa area and 15 wells (depths shallower than 11 m) in the Minami-shinagawa area. The geology of the two areas is similar, ranging mainly from gravel to silty sand, but the age of the public sewage system differs by up to 10 years between the two areas (1960s in the Kita-shinagawa area and 1970s in the Minami-shinagawa area). Water chemistry results showed that chloride ion ranged from 11.4 to 38.3 mg/L (Kita-Shinagawa area) and from 4.0 to 28.0 mg/L (Minami-Shinagawa area), nitrate ion from n.d. (not detected) to 22.4 mg/L (Kita-Shinagawa area) and from 7.2 to 38.1 mg/L (Minami-Shinagawa area), sulfate ion from 10.6 to 40.4 mg/L (Kita-Shinagawa area) and from 7.3 to 34.6 mg/L (Minami-Shinagawa area). The contribution of precipitation, water leakage and sewage leakage to groundwater recharge in the two areas was calculated using a three-component mixture analysis based on chloride ion concentrations and stable isotope ratios of water oxygen. The contribution of sewage leakage tended to be higher in the groundwater of the Kita-shinagawa area. The nitrogen stable isotope ratio of nitrate and sulfur stable isotope ratio of sulfate indicate that the groundwater in the Kita-shinagawa area is more reductive than that in the Minami-shinagawa area, and that denitrification and sulfate reduction reactions are ongoing in the groundwater in the Kita-shinagawa area. This suggests that the difference in the age of the public sewers in the two areas, namely the difference in the degree of aging of the public sewers, is the main cause of the distinct differences in groundwater quality and origin in the two areas, as described above.