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Inferring Heterogeneity in Aquitards Using High‐Resolution δD and δ 18 O Profiles
Author(s) -
Hendry M. Jim,
Wassenaar L.I.
Publication year - 2009
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.2009.00564.x
Subject(s) - piezometer , geology , borehole , hydraulic conductivity , pore water pressure , aquifer , diffusion , high resolution , mineralogy , tracer , soil science , geomorphology , groundwater , geotechnical engineering , soil water , thermodynamics , remote sensing , physics , nuclear physics
Vertical depth profiles of pore water isotopes (δD and δ 18 O) in clay‐rich aquitards have been used to show that solute transport is dominated by molecular diffusion, to define the timing of geologic events, and to estimate vertical hydraulic conductivity. The interpretation of the isotopic profiles in these studies was based on pore water samples collected from piezometers installed in nests (typically 4 to 15 piezometers) over depths of 10 to 80 m. Data from piezometer nests generally have poor vertical resolution (meters), raising questions about their capacity to reveal the impact of finer scale heterogeneities such as permeable sand bodies or fractured till zones on solute transport. Here, we used high‐resolution (30‐cm) depth profiles of δD and δ 18 O from two continuously cored boreholes in a till aquitard to provide new insights into the effects of sand bodies on solute transport. High‐resolution core‐derived profiles indicate that such heterogeneities can cause major deviations from one‐dimensional diffusion profiles. Further, comparison of piezometer‐measured values with best‐fit diffusion trends shows subtle deviations, suggesting the presence of heterogeneities that should not be ignored. High‐resolution profiles also more clearly defined the contact between the highly fractured oxidized zone and the underlying unoxidized zone than the piezometers.