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Carbon-14 age and chemical evolution of Ca(HCO3)2-type groundwater of age less than 8,000 years in a confined sandy and muddy Pleistocene aquifer, Japan
- Source :
- Hydrogeology Journal. 21:1289-1305
- Publication Year :
- 2013
- Publisher :
- Springer Science and Business Media LLC, 2013.
-
Abstract
- The Pleistocene Kimitsu aquifer was selected for examination of the relationship between groundwater age and chemical evolution of Ca(HCO3)2-type groundwater. For the most part, the aquifer is confined and composed mainly of quartz and feldspar with a small amount of calcite. The groundwater ages calculated by 14C were adjusted by using a carbon mass-balance method and corrected for effects of 14C diffusion. Groundwater ages in the Kimitsu aquifer vary from modern (upgradient) to approximately 2,400 years at 4.4 km from the edge of the recharge area. The 14C age was verified by groundwater velocity calculated from the hydraulic gradient and hydraulic conductivity. The confined groundwater evolved to Ca(HCO3)2-type around 50 years after recharge and this has been maintained for more than 8,300 years due to low chemical reactivity, derived from equilibrium with calcite, kaolinite and Ca-montmorillonite. In addition, high pH prevents the dissolution of Fe and Mn. Consequently, the rate of increase in electrical conductivity ranges from 10 to 30 μS/cm per 1,000 years. On the other hand, leakage from the deep region, which is recognized from high Cl– levels, causes remarkable increases in CH4 and HCO3 – concentrations, resulting in an apparent sulfidic zone at 500-m depth in most downgradient regions.
- Subjects :
- Calcite
Hydrology
geography
geography.geographical_feature_category
Hydrogeology
Artesian aquifer
Geochemistry
Aquifer
Groundwater recharge
chemistry.chemical_compound
Hydraulic head
Hydraulic conductivity
chemistry
Earth and Planetary Sciences (miscellaneous)
Groundwater
Geology
Water Science and Technology
Subjects
Details
- ISSN :
- 14350157 and 14312174
- Volume :
- 21
- Database :
- OpenAIRE
- Journal :
- Hydrogeology Journal
- Accession number :
- edsair.doi...........6cc9f49ee94ab690ac0e3866c5af4067