HR: 09:00h
AN: H21K-04    [Abstracts]
TI: Effects of Heterogeneities, Sampling Frequencies, Tools and Methods on Uncertainties in Subsurface Contaminant Concentration Measurements
AU: * Ezzedine, S M
EM: ezzedine1@llnl.gov
AF: WA/E&E Lawrence Liveremore National Lab, 7000 East Ave, Livermore, CA 94550,
AU: McNab, W W
EM: mcnab1@llnl.gov
AF: ERD, Lwarence Livermore National Lab, 7000 East Ave, Livermore, CA 94550,
AB: Long-term monitoring (LTM) is particularly important for contaminants which are mitigated by natural processes of dilution, dispersion, and degradation. At many sites, LTM can require decades of expensive sampling at tens or even hundreds of existing monitoring wells, resulting in hundreds of thousands, or millions of dollars per year for sampling and data management. Therefore, contaminant sampling tools, methods and frequencies are chosen to minimize waste and data management costs while ensuring a reliable and informative time-history of contaminant measurement for regulatory compliance. The interplay play between cause (i.e. subsurface heterogeneities, sampling techniques, measurement frequencies) and effect (unreliable data and measurements gap) has been overlooked in many field applications which can lead to inconsistencies in time- histories of contaminant samples. In this study we address the relationship between cause and effect for different hydrogeological sampling settings: porous and fractured media. A numerical model has been developed using AMR-FEM to solve the physicochemical processes that take place in the aquifer and the monitoring well. In the latter, the flow is governed by the Navier-Stokes equations while in the former the flow is governed by the diffusivity equation; both are fully coupled to mimic stressed conditions and to assess the effect of dynamic sampling tool on the formation surrounding the monitoring well. First of all, different sampling tools (i.e., Easy Pump, Snapper Grab Sampler) were simulated in a monitoring well screened in different homogeneous layered aquifers to assess their effect on the sampling measurements. Secondly, in order to make the computer runs more CPU efficient the flow in the monitoring well was replaced by its counterpart flow in porous media with infinite permeability and the new model was used to simulate the effect of heterogeneities, sampling depth, sampling tool and sampling frequencies on the uncertainties in the concentration measurements. Finally, the models and results were abstracted using a simple mixed-tank approach to further simplify the models and make them more accessible to field hydrogeologists. During the abstraction process a novel method was developed for mapping streamlines in the fractures as well within the monitoring well to illustrate mixing and mixing zones. Applications will be demonstrated for both sampling in porous and fractured media. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
DE: 1832 Groundwater transport
DE: 1847 Modeling
DE: 1849 Numerical approximations and analysis
DE: 1873 Uncertainty assessment (3275)
DE: 1894 Instruments and techniques: modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting