Uncertainty in NAPL volume estimates due to random measurement errors during partitioning tracer tests.
The uncertainty in NAPL volume estimates obtained through partitioning tracers can be quantified as a function of random errors in volume and concentration measurements when moments are calculated from experimentally measured breakthrough curves using the trapezoidal rule for numerical integration. The methodology is based upon standard stochastic methods for random error propagation. Monte Carlo simulations using a synthetic data set derived from the one-dimensional solution of the advective-dispersive equation serve to verify the process. It is shown that the uncertainty in NAPL volume predictions nonlinearly increases as the retardation factor decreases. An important result of this observation is that there is a large degree of uncertainty in using partitioning tracers to conclude NAPL is absent from the swept zone. Under the conditions investigated, random errors in concentration measurements are shown to have a greater impact on NAPL volume uncertainty than random errors in volume measurements, and it is also shown that uncertainty in NAPL volume decreases as the resolution of the breakthrough curves increases. The impact of uncertainty in background retardation (i.e., sorption of partitioning tracers in the absence of NAPL) was also investigated, and it likewise indicated that the relative uncertainty in NAPL volume estimates increases as the retardation factor decreases.
Brooks
Michael C
MC
U.S. Environmental Protection Agency, Kerr Research Center, P.O. Box 1198, Ada, Oklahoma 74820, USA.
Wise
William R
WR
D003198:Computer Simulation; D004784:Environmental Monitoring / Q000379:methods*; D004787:Environmental Pollution; D015233:Models, Statistical; D011849:Radioactive Tracers; D015203:Reproducibility of Results; D012989:Soil Pollutants; D014241:Trichloroethylene / Q000032:analysis; D035501:Uncertainty; D014865:Waste Disposal, Fluid; D014873:Water Pollutants; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification
D011849:Radioactive Tracers; D012989:Soil Pollutants; D014873:Water Pollutants; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene