Abstract:
Over the last few years, more than 40 partitioning interwell tracer tests (PITTs) have been
conducted at many different sites to measure nonaqueous phase liquid (NAPL) saturations in
the subsurface. While the main goal of these PITTs was to estimate the NAPL volume in the
subsurface, some were specifically conducted to assess the performance of remedial actions
involving NAPL removal. In this paper, we present a quantitative approach to assess the
performance of remedial actions to recover NAPL that can be used to assess any NAPL removal
technology. It combines the use of PITTs (to estimate the NAPL volume in the swept pore
volume between injection and extraction wells of a test area) withthe use of several cores
to determine the vertical NAPL distribution in teh subsurface. We illustrate the
effectiveness of such an approach by assessing the performance of a surfactant/foam flood
conducted at Hill Air Force Base, UT, to remove a TCE-rich NAPL from alluvium with
permeability contrasts as high as one order of magnitude. In addition, we compare the NAPL
volumes determined by the PITTs with volumes estimated through geostatistical interpolation
of aquifer sediment core data collected with a vertical frequency of 5-120 cm and a lateral
borehole spacing of 0.15 m. We demonstrate the use of several innovations including the
explicit estimation of not only the errors associated with NAPL volumes and saturations
derived from PITTs but also the heterogeneity of the aquifer sediments based upon
permeability estimates. Most importantly, we demonstrate the reliability of the PITT in
strongly heterogeneous aquifer sediments--a feature of particular importance at those sites
where the volume of NAPL-contaminated aquifer sediments is too large to afford soil coring
at a density of sampling that yields similar NAPL volumes as the PITT. Finally, the data
support the proposed performance assessment protocol for NAPL remediation combining the use
of PITTS and several aquifer sediment cores for vertical definition of the NAPL geometry.
Reference:
H.W. Meinardus, V. Dwarakanath, J. Ewing, G.J. Hirasaki, R.E. Jackson, M. Jin,
J.S. Ginn, J.T. Londergan, C.A. Miller, and G.A. Pope, "Performance Assessment of
NAPL Remediation in Heterogeneous Alluvium," Journal of Contaminant Hydrology, 54,
173-193, 2002.
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Last updated: April 25, 2002