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Uncertainty in NAPL volume estimates due to random measurement errors during partitioning tracer tests
Michael C Brooks1, William R Wise
1U.S. Environmental Protection Agency, Kerr Research Center, P.O. Box 1198, Ada, Oklahoma 74820, USA.
Environmental Science & Technology
|October 6, 2005
Summary
Quantifying uncertainty in non-aqueous phase liquid (NAPL) volume estimates using partitioning tracers is crucial. Higher uncertainty arises with lower retardation factors, impacting conclusions about NAPL presence.
Area of Science:
- Environmental Science
- Geochemistry
- Hydrogeology
Background:
- Non-aqueous phase liquids (NAPLs) pose environmental risks.
- Partitioning tracers are used to estimate NAPL volumes.
- Accurate NAPL volume estimation is critical for site remediation.
Purpose of the Study:
- To quantify the uncertainty in NAPL volume estimates derived from partitioning tracer data.
- To investigate the influence of measurement errors and parameters on NAPL volume uncertainty.
- To assess the reliability of partitioning tracers for determining NAPL absence.
Main Methods:
- Stochastic methods for random error propagation.
- Numerical integration of breakthrough curves using the trapezoidal rule.
- Monte Carlo simulations with synthetic data from advective-dispersive equation.
Main Results:
- Uncertainty in NAPL volume predictions increases nonlinearly as the retardation factor decreases.
- Random errors in concentration measurements have a greater impact than volume measurement errors.
- Uncertainty decreases with increased breakthrough curve resolution.
Conclusions:
- High uncertainty exists when using partitioning tracers to declare NAPL absence, especially with low retardation factors.
- Retardation factor significantly influences the reliability of NAPL volume estimates.
- Understanding error propagation is key for accurate NAPL site characterization.