Rapid exchange effects on isotope ratios in groundwater systems 2. Flow investigation using Sr isotope ratios

Thomas M. Johnson, Donald J. DePaolo

Research output: Contribution to journalArticle

Abstract

Sr isotope ratios were measured in groundwater, whole rock digestions, and cation exchange extracts from a clay-rich groundwater system at Ernest O. Lawrence Berkeley National Laboratory and were used to constrain flow velocities and search for preferential flow paths. In the Orinda formation siltstone, 87Sr/86Sr increases strongly over tens of meters along presumed flow paths, indicating slow groundwater flow. Dissolved Sr is close to isotopic equilibrium with the exchangeable Sr in the clays, and the observed 87Sr/86Sr increase is interpreted as a cation exchange front moving slowly through the unit combined with dissolution of minerals with relatively high 87Sr/86Sr ratios. The data are inverted using a one- dimensional transport-dissolution-exchange model; the results indicate long- term average flow velocities of less than 0.2 m/yr which are consistent with 14C measurements. The data suggest a lack of strong preferential flow paths through this unit.

Original languageEnglish (US)
Pages (from-to)197-209
Number of pages13
JournalWater Resources Research
Volume33
Issue number1
DOIs
StatePublished - Jan 1997
Externally publishedYes

ASJC Scopus subject areas

  • Water Science and Technology

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