Abstract:
In 1995, a partitioning interwell tracer test was conducted in the vadose zone beneath
two buried organic liquid disposal trenches at Sandia National Laboratories in New
Mexico. The purpose was to estimate the amount and distribution of trichloroethylene
(TCE) trapped by capillary forces as residual dense nonaqueous phase liquid (DNAPL).
Screened injection and extraction wells, placed 16.8 m apart, and two monitor wells
with multilevel sampling capability allowed vertical testing from 3.0 to 24.4 m below
ground surface. Seven tracers were injected, but the most useful tracers in the final
analysis were sulfur hexafluoride (nonpartitioning), perfluoro-1,3,5-trimethylcyclohexane
(TCE-partitioning), and difluoromethane (water-partitioning). Both a TCE-partitioning
tracer and a water-partitioning tracer were needed to determine average TCE DNAPL
saturation. Average saturations of DNAPL and water were measured to be 0.11 +/- 0.02%
and 23 +/- 2.0%, respectively, in the shallow zone between 3.0 and 10.7 m. Monitor well
data showed no evidence of DNAPL below a depth of 9 m. These results had important
implications for remedial actions at the site.
Reference:
P.E. Mariner, M. Jin, J.E. Studer, and G.A. Pope, "The First Vadose Zone Partitioning
Interwell Tracer Test (PITT) for NAPL and Water Residual," Environmental Science &
Technology, 33 (16), 2825-2828, 1999.
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Last updated: May 2, 2002