Open AccessField Evidence for Strong Chemical Separation of Contaminants in the Hanford Vadose Zone
Author(s) -
Conrad Mark E.,
DePaolo Donald J.,
Maher Katharine,
Gee Glendon W.,
Ward Anderson L.
Publication year - 2007
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2007.0007
Subject(s) - vadose zone , tracer , capillary fringe , borehole , bromide , pore water pressure , hanford site , geology , contamination , mineralogy , infiltration (hvac) , environmental chemistry , chemistry , hydrology (agriculture) , soil water , soil science , radioactive waste , geotechnical engineering , materials science , nuclear chemistry , ecology , physics , organic chemistry , biology , nuclear physics , composite material
Water and chemical transport from a point source within vadose zone sediments at the Hanford Site in Washington State were examined with a leak test consisting of five 3800‐L aliquots of water released at 4.5‐m depth every week over a 4‐wk period. The third aliquot contained bromide, D 2 O, and 87 Sr. Movement of the tracers was monitored for 9 mo by measuring pore water compositions of samples from boreholes drilled 2 to 8 m from the injection point. Graded sedimentary layers acting as natural capillary barriers caused significant lateral spreading of the leak water. Shortly after injections were completed, D 2 O was found at the 9‐ to 11‐m depth at levels in excess of 50% of the tracer aliquot concentration, while sediment layers with elevated water content at the 6‐ to 7‐m depth had less than 3% of the D 2 O tracer concentration, suggesting deep penetration of the D 2 O tracer and limited mixing between different aliquots of leak fluids. Initially, high bromide concentrations decreased more rapidly over time than D 2 O, suggesting enhanced transport of bromide due to anion exclusion. No significant increase in 87 Sr was detected in the sampled pore water, indicating strong retardation of Sr by the sediments. These results highlight some of the processes strongly affecting chemical transport in the vadose zone and demonstrate the significant separation of contaminant plumes that can occur.