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| Titel |
Dissolved Gas Composition of Groundwater in Taipei Basin and its implications |
| VerfasserIn |
Nga-Chi Cheung, Tsanyao Frank Yang, Ai-Ti Chen, Wen-Fu Chen, Yun-Shuen Wang |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106374
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| Publikation (Nr.) |
 EGU/EGU2015-6043.pdf |
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| Zusammenfassung |
| This study is the first comprehensive analysis for dissolved gases of groundwater in Taipei
Basin, northern Taiwan. In addition to conventional water chemistry, the dissolved-gas
compositions of groundwater from 34 observation wells have been systematically
analyzed. The relationship between dissolved gases and geological environment, and
probable sources of the gases are discussed in this study. According to the water
chemistry data of Piper plot, most of the groundwater samples in this study can be
classified as Ca(HCO3)2 and NaHCO3 types. Several samples exhibit NaCl type
characteristic which reveals the mix with seawater. Isotopic compositions of hydrogen
and oxygen for groundwater, surface water and meteoric water in Taipei Basin are
aligned with Local Meteoric Water Line (LMWL), which indicates that they are
influenced by meteoric water. Composition of groundwater in the southern part of
the basin has similar characteristics with surface water. However, stratifications
occurred in the observation wells from northern part of the basin. It reveals different
recharge sources for groundwater samples in northern basin with the southern basin.
Based on the major dissolved gases compositions, three major components are
identified which are CH4, N2 and CO2. The d13C of dissolved inorganic carbon
(DIC) indicates microbial activities are dominant in the studied area. Dissolved
radon concentrations are in the range of 200 - 20,667 Bq/m3 in the studied area
and the deeper well usually exhibits a higher radon value than the shallow one
from the same site. Several sites with high radon values are correlated with the
locations of fault zones, which may provide the conduit for deeper gas migrate to
shallower aquifers. The groundwater samples from northern part of the basin exhibit
unexpectedly high helium isotopic ratios (RA >2, where RA is the 3He/4He ratio of
air). Samples from five observation wells have RA values more than 3 RA and the
highest one is 4.2 RA, which probably the highest 3He/4He values ever reported in
groundwater samples from basin area. The high RA ratios represent signals from
mantle and the source of excess 3He may come from Tatun volcanic group (TVG)
which located at the north side of Taipei Basin. Alternatively, the nearby active
Shanchiao Fault may provide a pathway for mantle fluids invaded into the basin. |
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