Journal
JOURNAL OF HYDROLOGY
Volume 609, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.jhydrol.2022.127755
Keywords
Groundwater age; Chlorofluorocarbons; Sulfur hexafluoride; Tritium; Helium; Hawai'i
Funding
- Hawai'i EPSCoR Program - National Science Foundation Research Infrastructure Improvement Award (RII) Track-1: 'Ike Wai: Securing Hawai`i's Water Future Award [OIA-1557349]
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The geologically complex western aquifers of Hawai'i Island serve as the primary reservoir of fresh potable water for residents, yet the area's hydrogeologic characteristics are still not well understood. This study implemented a multi-tracer approach to estimate the apparent ages of groundwater in the West Hawai'i aquifers. The results showed the presence of both young and old groundwater, with important implications for groundwater management.
The geologically complex western aquifers of Hawai'i Island serve as the primary reservoir of fresh potable water for residents, yet the area's hydrogeologic characteristics are still not well understood. Groundwater age is a fundamental parameter used to better understand groundwater flow and storage, yet few studies have attempted to estimate apparent groundwater ages in Hawai'i. This study implements a multi-tracer approach using chlo-rofluorocarbons, sulfur hexafluoride, and tritium/helium-3 to determine the apparent ages of young water masses from the West Hawai'i aquifers. Chlorofluorocarbon and tritium/helium-3 tracer measurements suggest that the aquifers contain young groundwater with a median age of 53 years, but that a significant volume of older groundwater exists, which was recharged prior to the release of these anthropogenic tracers. Mixing models suggest that the groundwater consists of mixtures with an average 28% modern water (< 70 years), with the remainder being recharged prior to 1953. Further, helium measurements demonstrate that the area's ground-water is influenced by hydrothermal and magmatic processes from Huala over bar lai volcano, which bias estimated groundwater ages if not properly considered. It is therefore beneficial to utilize a multi-tracer approach in an oceanic volcanic island setting, where groundwater ages are impacted by various external processes. The analysis of young apparent ages and proportions can aid in coastal aquifer characterization and subsequent groundwater quality assessment and is crucial for sustainable groundwater management.
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