UBC Theses and Dissertations
The worth of data in predicting aquitard continuity in hydrogeolgical design James, Bruce Rennie
A Bayesian decision framework is developed for addressing data worth questions for hydrogeological design in heterogeneous geological environments. This framework is developed specifically for aiding hydrogeologists, dealing with groundwater contamination, in the design of exploration programs searching for aquitard discontinuities. It can be used to evaluate, and compare, the cost effectiveness of (a) patterns of precise point measurements (e.g. boreholes), which are often expensive, and (b) areal geophysical surveys which are imprecise, but usually less expensive. The framework consists of two basic modules: a geostatistical indicator algorithm for simulating aquitard heterogeneity and a numerical model for simulating contaminant transport. Bayesian decision analysis ties these two modules together. The Bayesian nature of the framework also provides a methodology for combining a conceptual understanding of the local geology with quantitative information. Indicator geostatistics allows the handling of hydrogeological parameters which behave in space as non-Gaussian random variables. The estimated worth of a measurement was found to be particularly sensitive to economic parameters. It was less sensitive to hydrogeological and geostatistical parameters. The framework was applied in a retrospective fashion to the design of a remediation program for soil contaminated by radioactive waste disposal at the Savannah River Site, in South Carolina. The cost effectiveness of different patterns of point measurements was studied. This study included determining the number and spacing of the most cost effective pattern. Contour maps were produced of the net worth of a single, point measurement. These contour maps can be used to design sequential sampling programs involving single or multiple measurements. Good potential was also shown for determining the cost effectiveness of an a real geophysical survey. The net worth of patterns of precise, point measurements was compared to that of an imprecise, a real seismic survey. These results indicate that the framework can be very valuable in determining if additional exploration is cost effective and in designing efficient exploration programs. Results also show that ignoring a conceptual understanding of geology can lead to erroneous data worth analysis. The framework could be modified to handle other data worth questions in hydrogeology or other disciplines, such as mining, or petroleum reservoir engineering.
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