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Uncertainty and Sensitivity Analyses of Groundwater Travel Time in a Two-Dimensional Variably-Saturated Fractured Geologic Medium

Published online by Cambridge University Press:  01 January 1992

A. B. Gureghian  and
B. Sagar
A. B. Gureghian
Affiliation:
Center for Nuclear Waste Regulatory Analyses, 6220 Culebra Road, San Antonio, Texas 78228-0510
B. Sagar
Affiliation:
Center for Nuclear Waste Regulatory Analyses, 6220 Culebra Road, San Antonio, Texas 78228-0510
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Abstract

This paper presents a method for sensitivity and uncertainty analyses of a hypothetical nuclear waste repository located in a layered and fractured unconfined aquifer. Groundwater travel time (GWTlT) has been selected as the performance measure. The repository is located in the unsaturated zone, and the source of aquifer recharge is due solely to steady infiltration impinging uniformly over the surface area that is to be modeled. The equivalent porous media concept is adopted to model the fractured zone in the flow field. The evaluation of pathlines and travel time of water particles in the flow domain is performed based on a Lagrangian concept. The Bubnov-Galerkin finite-element method is employed to solve the primary flow problem (non-linear), the equation of motion, and the adjoint sensitivity equations. The matrix equations are solved with a Gaussian elimination technique using sparse matrix solvers. The sensitivity measure corresponds to the first derivative of the performance measure (GWTT) with respect to the parameters of the system. The uncertainty in the computed GWTT is quantified by using the first-order second-moment (FOSM) approach, a probabilistic method that relies on the mean and variance of the system parameters and the sensitivity of the performance measure with respect to these parameters. A test case corresponding to a layered and fractured, unconfined aquifer is then presented to illustrate the various features of the method.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 294: Symposium V – Scientific Basis for Nuclear Waste Management XVI , 1992 , 921
Copyright
Copyright © Materials Research Society 1993

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References

REFERENCES

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