Using ⁸¹Kr and isotopic tracers to characterise old groundwater in the Bangkok metropolitan and vicinity areas

ABSTRACT

Krypton-81 was applied to investigate the age of groundwater in the aquifer system in the Bangkok metropolitan and vicinity areas. Stable (²H, ¹⁸O and ¹³C) and radioactive (³H, ⁸⁵Kr and ¹⁴C) isotopes and noble gases were applied in parallel. Low levels of ¹⁴C and significant radiogenic ⁴He confirm that groundwater in the deep aquifers is older than 30 ka. ⁸¹Kr analysis identified groundwater with ages ranging from 17 to 300 ka. At some sites, large age discrepancies between ⁸¹Kr and ¹⁴C indicated that inter-aquifer mixing is likely occurring. The interpretation of the noble gases suggests that groundwaters in the deeper aquifers, with apparent ages of 300 to 10 ka, have recharged in slightly colder and wetter climates than those found in the upper aquifers with apparent ages < 10 ka. Degradation of water quality from seawater intrusion was identified in the upper four aquifers. This was also evidenced by higher δ¹⁸O and δ²H values, typical of seawater. The four deeper aquifers contain high quality water characterised by less enriched ¹⁸O and ²H. This work presents new findings of very old groundwater in the Bangkok aquifer system.

KEYWORDS:

• Thailand
• groundwater age
• krypton-81
• carbon-14
• noble gases
• Lower Chao Phraya Basin

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

We thank the International Atomic Energy Agency for funding this study under the Technical Cooperation Project THA-16879. KK, MY, CS, PC, CP and NU were supported by the Thailand Institute of Nuclear Technology. JACA was supported by Spiez Laboratory, Swiss Federal Office for Civil Protection. OO, VH and AW were supported by the Department of Groundwater Resources of the Thailand Ministry of Natural Resources and Environment. JCZ and PM were supported by the US Department of Energy, Office of Nuclear Physics, under contract DE-AC02-06CH11357.