HR: 0800h
AN: H41E-0458    [Abstracts]
TI: A Cost-effective Method for Characterizing NAPL Source Zones -- Hydraulic/Tracer Tomography
AU: * Zhu, J
EM: junfeng@email.arizona.edu
AF: University of Arizona, 1133 E. North Campus Drive, Tucson, AZ 85721
AU: Yeh, T J
EM: yeh@hwr.arizona.edu
AF: University of Arizona, 1133 E. North Campus Drive, Tucson, AZ 85721
AB: We develop a hydraulic/tracer tomography technology to map detailed spatial distribution of contaminants (e.g., non-aqueous liquids, NAPLs) in the subsurface. A hydraulic tomography survey sequentially injects or pumps water at selected locations and observes head responses at other locations. In a similar way to hydraulic tomography, a tracer tomography survey sequentially injects nonreactive and partitioning tracers and monitors tracer breakthroughs in a NAPL source zone. NAPL saturation in the subsurface generally controls differences in behaviors of the nonreactive and partitioning tracer breakthroughs. Thus, the breakthroughs can be used to estimate possible locations and concentrations of NAPLs. Tomography surveys merely enhance the estimation by mapping the NAPLs at different angles and perspectives. To quantitatively interpret the large volume of concentration data sets from the tracer tomography, an inverse method is developed. The method is an extension of the sequential successive linear estimator (SSLE, Yeh and Liu 2000, Zhu and Yeh, 2005) used for interpreting data from hydraulic tomography. In our inverse approach, the spatial variability of hydraulic properties is first estimated by using hydraulic tomography; porosity then is estimated using nonreactive tracer breakthroughs from tracer tomography; NAPL saturation is lastly estimated using partitioning tracer breakthroughs from tracer tomography also. The inverse method seeks mean porosity and NAPL saturation conditioned on concentration observations, prior knowledge of structures, and parameter measurements. The inverse technique was tested on a synthetic aquifer contaminated with NAPLs. Results show that, with only a limited number of wells, this technology successfully captures the major spatial patterns of both porosity and NAPL distribution. Although field situations are more complicated than the synthetic case, the primary results from the synthetic case demonstrate that the tracer tomography combining with SSLE method potentially is a viable and cost-effective tool for subsurface contaminant characterization.
DE: 1800 HYDROLOGY
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1869 Stochastic hydrology
SC: Hydrology [H]
MN: Fall Meeting 2005