『Summary
　Deterioration of the quality of groundwater under urban areas has become a major environmental concern worldwide. This paper presents a pilot case study (in the Taipei urban area) using multiple stable isotopes (δD-H2O and δ¹⁸O-H2O, δ¹⁵N-NO3 and δ¹⁸O-NO3, δ³⁴S-SO4 and δ¹⁸O-SO4, and ⁸⁷Sr/⁸⁶Sr) with the aim of understanding the subsurface nature and environmental status of such areas. A previous study has already characterized Taipei shallow groundwaters as sulfate-rich in comparison to other Southeast Asian metropolitan cities. Our chemical measurements clarified that the arsenic is the important environmental concerns in the aquifers. Dual isotope approaches for nitrate and sulfate suggested these ions were sourced mainly from municipal sewage leaking from sewer pipes in urbanized area, while chemical fertilizers applied in the local agricultural fields partly contribute in the suburb area. Significant decreases in nitrate and sulfate concentrations due to denitrification and sulfate reduction were observed in some groundwaters, which induced increases in isotope ratios up to 24.9‰ for δ¹⁵N-NO3 and 27.2‰ for δ³⁴S-SO4. Nitrate groundwater pollution in the Taipei Basin is not a subject of serious concern (＜44 mg/L limit for NO3^- for all analyzed samples) at the present time due to attenuation by denitrification. However, arsenic is preferentially released in groundwater (＞100μg/L) in anoxic environment under which sulfate reduction occurs. The Sr isotope data suggested that the arsenic is derived from alluvial deposits of Oligocene-Miocene sedimentary rock origin. This study disclosed the complex causes of environmental changes in Taipei urban shallow groundwater. It is also important as an excellent case study demonstrating the efficient use of multiple isotope diagnosis in the urban groundwater environmental field.

Keywords: Taipei; Urban environment; Groundwater; Water quality; Multi isotope』

1. Introduction
2. Outline of study area
3. Sampling and processing
4. Methods
5. Results and discussion
　5.1. Origins of Taipei shallow groundwater
　5.2. Origins and attenuation of nitrate pollution
　5.3. Sources of sulfate and occurrence of sulfate reduction
　　5.3.1. Isotopic characterization of the source materials
　　5.3.2. Sources of sulfate in river and spring waters
　　5.3.3. Sources of sulfate in shallow groundwaters
　　5.3.4. Behaviors of sulfate, arsenic and lead in shallow groundwaters
　5.4. Variation of ⁸⁷Sr/⁸⁶Sr ratios and the origin of arsenic
6. Conclusions
Acknowledgments
References