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Scientific Investigations Report 2009-5057

Prepared in cooperation with the City of Portland Bureau of Environmental Services

Tritium/Helium-3 Apparent Ages of Shallow Ground Water, Portland Basin, Oregon, 1997–98

By Stephen R. Hinkle

Abstract

Water samples for tritium/helium-3 age dating were collected from 12 shallow monitoring wells in the Portland basin, Oregon, in 1997, and again in 1998. Robust tritium/helium-3 apparent (piston-flow) ages were obtained for water samples from 10 of the 12 wells; apparent ages ranged from 1.1 to 21.2 years. Method precision was demonstrated by close agreement between data collected in 1997 and 1998. Tritium/helium-3 apparent ages generally increase with increasing depth below the water table, and agree well with age/depth relations based on assumptions of effects of recharge rate on vertical ground-water movement.

For additional information contact:
Director, Oregon Water Science Center
U.S. Geological Survey
2130 SW 5th Avenue
Portland, Oregon 98402
http://or.water.usgs.gov

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Suggested citation:

Hinkle, S.R., 2009, Tritium/helium-3 apparent ages of shallow ground water, Portland basin, Oregon, 1997–98: U.S. Geological Survey Scientific Investigations Report 2009-5057, 8 p.



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