9:55 AM - 10:10 AM
[AHW23-08] On sulfate ion concentration and its origin in shallow groundwater in Shinagawa, Central Tokyo, Japan
Keywords:urban, shallow groundwater, sulfate , sewage leakage, sulfate reduction reaction, mixing analysis
During the period of rapid economic growth, excessive pumping of urban groundwater caused severe land subsidence, and to this day, Tokyo and other major cities in Japan have strictly limited groundwater pumping (Morita, 2012). However, since the Great Hanshin-Awaji Earthquake in 1995, there has been growing interest in using urban groundwater, especially shallow groundwater, as a source of disaster and emergency water (Yasuhara, 1997; Kuroda et al., 2008; Yasuhara, 2008). Furthermore, the use of groundwater to mitigate the urban heat island effect and to create and preserve a hydrophilic environment is also attracting attention (Sugie et al., 2005). However, there are many unknowns regarding the actual conditions of groundwater quality and the amount of groundwater available for groundwater use. Therefore, we are conducting research on shallow groundwater in the Kita-Shinagawa and Minami-Shinagawa areas of Shinagawa, Central Tokyo, to understand the actual status of urban groundwater chemistry and its seasonal changes, and to elucidate the water chemistry formation process and the origin of urban groundwater. In this presentation, we focus on SO42- in urban groundwater and discuss its origin and the process of concentration change.
Shallow groundwater were collected from eight wells in the Kita-Shinagawa area and three wells in the Minami-Shinagawa area (all shallower than 12 m) in August 2021 and February 2022 (drought period). The results of various water chemistry and δ34S analyses showed that SO42- concentrations ranged from 10.7 mg/L (N2) to 40.4 mg/L (N9) in August, 10.6 mg/L (N2) to 62.6 mg/L (N4) in February, NO3- concentrations were undetectable (N2) to 22.4 mg/L (N6) in August, in Cl- concentrations were 6.9 mg/L (S11) to 38.3 mg/L (N2) in August and 5.6 mg/L (S11) to 39.2 mg/L (N2) in February. The δ34S values for each site and season were significantly different: -4.9‰ (N9) to 23.8‰ (N2) in August, and -5.9‰ (N4) to 21.2‰ (N2) in February. This may be attributed to differences in the contribution rates of precipitation seepage water, water supply leakage, and sewage leakage at each site. Since δ34S was high at N2 in the Kita-shinagawa area (about 20 ‰ or more in February and August), we investigated the occurrence and progress of the sulfate reduction reaction. The relationship between SO42- concentration and δ34S based on the Rayleigh equation indicates that the sulfate reduction reaction occurred and progressed significantly at N2. The concentration of SO42- in groundwater in the study area is determined by the difference in the contribution rate of rainfall infiltration, water supply leakage, and sewage leakage, and the concentration is considered to change secondary to the occurrence and progression of the sulfate reduction reaction.
Shallow groundwater were collected from eight wells in the Kita-Shinagawa area and three wells in the Minami-Shinagawa area (all shallower than 12 m) in August 2021 and February 2022 (drought period). The results of various water chemistry and δ34S analyses showed that SO42- concentrations ranged from 10.7 mg/L (N2) to 40.4 mg/L (N9) in August, 10.6 mg/L (N2) to 62.6 mg/L (N4) in February, NO3- concentrations were undetectable (N2) to 22.4 mg/L (N6) in August, in Cl- concentrations were 6.9 mg/L (S11) to 38.3 mg/L (N2) in August and 5.6 mg/L (S11) to 39.2 mg/L (N2) in February. The δ34S values for each site and season were significantly different: -4.9‰ (N9) to 23.8‰ (N2) in August, and -5.9‰ (N4) to 21.2‰ (N2) in February. This may be attributed to differences in the contribution rates of precipitation seepage water, water supply leakage, and sewage leakage at each site. Since δ34S was high at N2 in the Kita-shinagawa area (about 20 ‰ or more in February and August), we investigated the occurrence and progress of the sulfate reduction reaction. The relationship between SO42- concentration and δ34S based on the Rayleigh equation indicates that the sulfate reduction reaction occurred and progressed significantly at N2. The concentration of SO42- in groundwater in the study area is determined by the difference in the contribution rate of rainfall infiltration, water supply leakage, and sewage leakage, and the concentration is considered to change secondary to the occurrence and progression of the sulfate reduction reaction.