This study investigated the use of radon-222 as an in situ partitioning tracer for
quantifying nonaqueous phase liquid (NAPL) saturations in the subsurface.
Laboratory physical aquifer models (PAMs), field experiments, and numerical
simulations were used to investigate radon partitioning in static (no-flow) experiments
and in single-well, 'push-pull' tests conducted in non-contaminated and NAPL-contaminated
aquifers. Laboratory push-pull tests in a wedge-shaped PAM and field
push-pull tests in a NAPL-contaminated aquifer showed that radon was retarded in the
presence of NAPL, with retardation manifested in increased dispersion of radon
extraction phase breakthrough curves (BTCs). An approximate analytical solution to
the governing transport equation and numerical simulations provided estimates of the
radon retardation factor (R), which was used to calculate NAPL saturations (S[subscripts n]).
Laboratory static and push-pull tests were conducted in a large-scale
rectangular PAM before and after NAPL contamination, and after alcohol cosolvent
flushing and pump-and-treat remediation. Radon concentrations in static tests were
decreased due to partitioning after NAPL contamination and increased after
remediation. Push-pull tests showed increased radon retardation after NAPL
contamination; radon retardation generally decreased after remediation. Numerical
simulations modeling radon as an injected or ex situ partitioning tracer were used to
estimate retardation factors and resulted in overestimations of the likely S[subscripts n] in the
PAM. Radon partitioning was sensitive to changes in S[subscripts n] in both static and push-pull
tests. However, the test results were sensitive to test location, sample size, test design,
and heterogeneity in S[subscripts n] distribution.
Numerical simulations of hypothetical push-pull tests conducted in a NAPL-contaminated
aquifer were used to investigate the influence of homogeneous and
heterogeneous S[subscripts n] distributions and initial radon concentrations on radon BTCs and
resulting S[subscripts n] calculations. Both of these factors were found to affect radon BTC
behavior. A revised method of plotting and interpreting radon BTCs combined with
numerical simulations modeling radon as an in situ partitioning tracer (incorporating
initial radon concentrations into the model as a function of S[subscripts n]) were used to re-analyze
laboratory and field push-pull test BTCs. This method reduced the overestimation of
calculated S[subscripts n] values from laboratory tests. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31801 |
| Date | 30 January 2003 |
| Creators | Davis, Brian M. |
| Contributors | Semprini, Lewis |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0147 seconds