Site-Specific Seismic Site Response Model for the Waste Treatment Plant, Hanford, Washington Page: 4 of 158
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The seismic design for the Waste Treatment Plant (WTP) on the Hanford Site near Richland, Washington,
is based on an extensive probabilistic seismic hazard analysis conducted in 1996 by Geomatrix
Consultants, Inc. In 1999, the U.S. Department of Energy Office of River Protection (ORP) approved this
design basis following revalidation reviews by British Nuclear Fuels, Ltd., and independent reviews by
seismologists from the U.S. Army Corps of Engineers and Lawrence Livermore National Laboratory.
In subsequent years, the Defense Nuclear Facilities Safety Board (DNFSB) staff has questioned the
assumptions used in developing the seismic design basis, particularly the adequacy of the site
geotechnical surveys. The Board also raised questions about the probability of local earthquakes and the
adequacy of the "attenuation relationships" that describe how earthquake ground motions change as they
are transmitted to the site. The ORP responded with a comprehensive review of the probability of
earthquakes and the adequacy of the attenuation relationships. However, the DNFSB remained concerned
that "the Hanford ground motion criteria do not appear to be appropriately conservative." Existing site-
specific shear wave velocity data were considered insufficient to reliably use California earthquake
response data to directly predict ground motions at the Hanford Site.
To address this remaining concern, the ORP provided a detailed plan in August 2004. Key features of
this plan included acquiring site-specific soil data down to approximately 500 feet, reanalyzing the effects
of deeper layers of sediments interbedded with basalt (down to about 2,000 feet) that may affect the
attenuation of earthquake ground motion more than previously assumed, and applying new models for
how ground motions attenuate as a function of magnitude and distance at the Hanford Site.
This interim report documents the collection of site-specific geologic and geophysical data characterizing
the WTP site and the modeling of the WTP site-specific ground motion response.New geophysical data
were acquired, analyzed, and interpreted with respect to existing geologic information gathered from
other Hanford-related projects in the WTP area. Existing data from deep boreholes were assembled and
interpreted to produce a model of the deeper rock layers consisting of interlayered basalts and
sedimentary interbeds. These data were analyzed statistically to determine the variability of seismic
velocities and then used to randomize the velocity profiles. New information obtained from records of
local earthquakes at the Hanford Site was used to constrain site response models. The earthquake ground
motion response was simulated on a large number of models resulting from a weighted logic tree
approach that addresses the geologic and geophysical uncertainties. Weights were chosen by the working
group described in the acknowledgements. Weights were based on the strength or weakness of the
available data for each combination of logic tree parameters. Finally, interim design ground motion
spectra were developed to envelope the remaining uncertainties.
The results of this study demonstrate that the site-specific soil structure (Hanford and Ringold formations)
beneath the WTP is thinner than was assumed in the 1996 Hanford Site-wide model. This thinness
produces peaks in the response spectra (relative to those in 1996) near 2 Hz and 5 Hz. The soil
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Rohay, Alan C. & Reidel, Steve P. Site-Specific Seismic Site Response Model for the Waste Treatment Plant, Hanford, Washington, report, February 24, 2005; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc777787/m1/4/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.