**\[DNFSB LETTERHEAD\]**

January 21, 2003

The Honorable Jessie Hill Roberson

Assistant Secretary for Environmental Management

U.S. Department of Energy

1000 Independence Avenue, SW

Washington, DC 20585-0113

Dear Ms. Roberson:

The Defense Nuclear Facilities Safety Board (Board), in its letter of
December 16, 2002, requested a report describing how structural design
margins will be managed as a function of design uncertainties for the
Waste Treatment Plant (WTP). This request was based, in part, on the
Board's concerns regarding seismic-related design load uncertainties.
The Board has completed its assessment of the WTP ground motion design
criteria and, working with the Department of Energy (DOE) and contractor
personnel, has resolved most of the technical issues involved. However,
one issue remains.

The current site response analysis is based on the premise that the site
response characteristics of the soils underlying the Hanford Site 200
areas are similar to those represented in California. However, there is
a large uncertainty in the data using this approach, and analysis of the
existing data shows that the Hanford Site response in the frequency
range of 4 to 10 Hz is about 15 percent greater than that of California
sites. The Hanford ground motion criteria do not appear to be
appropriately conservative.

The Board understands that the WTP contractor has implemented acceptably
conservative compensatory design features to account for uncertainty in
the seismic design criteria. The Board believes this conservatism must
be maintained for all future design work at Hanford (e.g., future waste
treatment capabilities) unless site-specific attenuation relationships
are developed.

The enclosed report on this issue is provided for your use should you
elect to reassess the

Hanford ground motion criteria in order to reduce the design
conservatism for future defense nuclear facilities. Properly executed,
this work would justify a lowering of compensatory design conservatism.
Please contact me if you have any questions on this matter.

Sincerely,

***John T. Conway***

***Chairman***

c: Mr. Roy J. Schepens

Mr. Keith A. Klein

Mr. Mark B. Whitaker, Jr.

Enclosure

**DEFENSE NUCLEAR FACILITIES SAFETY BOARD**

**Staff Issue Report**

January 3, 2003

**MEMORANDUM FOR:** J. K. Fortenberry, Technical Director

**COPIES:** Board Members

**FROM:** J. Blackman

**SUBJECT:** Ground Motion Criteria for the Hanford Waste Treatment
Plant

This report documents the results of reviews performed by the staff of
the Defense Nuclear Facilities Safety Board (Board) of the Waste
Treatment Plant (WTP) at the Hanford Site. Staff members J. Blackman and
S. Stokes and outside expert P. Rizzo participated in these reviews.

**Background.** Beginning in March 2002, several meetings and telephone
conferences were conducted to discuss the ground motion criteria used in
the design of the WTP. These criteria are contained in *Probabilistic
Seismic Hazard Analysis*, *DOE Hanford Site*, *Washington*,
WHC-SD-W236A-TI-002, Rev. lA, October 1996. Issues identified by the
Board's staff are outlined in the attachment to this report. All issues
have been addressed, with the exception of the approach used to develop
attenuation relationships for deep geologic formations to characterize
the Hanford Site seismic hazard (items 7 and 8).

**Discussion.** The site response analysis used in the above report is
based on the premise that the site response characteristics of the soils
underlying the Hanford Site 200 East and 200 West areas are similar to
those represented in California time-history strong motion data.
Comparative analyses of the response of the Hanford profiles and the
generic California profiles to the same input motions (e.g., time
histories) were performed using the computer program SHAKE 2000.[^1]
Log-log plots of median spectral amplification ratios versus period were
developed (e.g., Hanford profiles and the generic California profiles).
From these plots it was concluded that the Hanford ground motion sites,
which are also underlain by deep soil deposits, are similar to ground
motions on California deep soil sites with an uncertainty of ±20
percent. However, the Hanford Site exhibits considerably more
amplification at certain frequencies (as much as 50 percent) than sites
in California used to develop the attenuation relationships.

In an attempt to resolve this issue, a reanalysis was performed using a
larger group of time histories and taking into account a broader range
of soil properties to better characterize expected behavior. It was
anticipated that this approach would result in a more uniform
amplification over the entire frequency range of interest. Linear plots
of median spectral amplification ratios versus period were developed
(e.g., Hanford profiles and the generic California profiles) using a
range of soil properties based on actual measured data at the WTP. The
results, however, indicated that the site response at Hanford is about
15 percent greater than that at California sites in the frequency range
of 4 to 10 Hz while frequency ranges below 4 Hz and greater than 10 Hz
showed some attenuation. Based on these results, DOE did not incorporate
these additional changes in the WTP design ground motion. However, in
anticipation of such underestimates, the Board's staff understands that
the WTP designers increased the seismic loads by 15 percent. This is an
acceptable compensatory measure for the WTP, as discussed in the Board's
letter of July 30, 2002.

**Conclusions.** The Board's staff does not believe that the Hanford
ground motion criteria are appropriately conservative. While the staff
understands that compensatory measures were implemented for the WTP, all
future design work at Hanford, such as future waste treatment
capabilities, ought to incorporate similar compensatory measures or
develop site- specific attenuation relationships.

DOE Order 420.1A, *Facility Safety* (Section 4.4.4―"Natural Phenomena
Hazards

Assessment") requires that natural phenomena hazard reassessments be
conducted if there are significant changes in the natural phenomena
hazard assessment methodology or site-specific information. The Order
also suggests that natural phenomena hazard assessments be reviewed and
updated, as necessary, at least every 10 years for existing sites. Work
on the current Hanford seismic hazard assessment was begun in the early
1990s. Since that time, new approaches and methodologies, such as the
technology for using source-to-site attenuation relationships and
site-specific amplification studies, have been developed to the point
that they are considered standard practice for probabilistic seismic
hazard analysis and for the development of design response spectra. In
addition, there is an improved understanding of the tectonics at
Hanford, including an association of local seismicity with the Yakima
Folds and more data pertaining to slip rates. Improved technology and
better understanding of tectonics indicate the need for a reassessment
of the seismic hazard at Hanford in accordance with the Order.

At a minimum, a proper reassessment would consist of the following:

-   A formal site investigation would be conducted, suitable for
    site-specific response analysis with new deep borings, shear wave
    velocity measurements, and laboratory tests (modulus degradation and
    damping). The borings would be deep enough to adequately
    characterize in detail the upper 1000 ft of the Columbia River
    Basalt Group (CRBG); geophysical measurements would be performed to
    characterize the entire CRBG and correlated with the deep borings
    (the existing borings and shear wave velocity data are not deep
    enough for proper characterization of the CRBG).

-   A randomized profile would be developed, similar to that developed
    for the site-wide seismic hazard analysis at the Savannah River
    Site.

-   Earthquake sources and associated source parameters would be
    defined, with proper consideration of the range of uncertainty.

-   Hanford-specific source-to-site attenuation relationships would be
    developed. If these relationships stem from California data, the
    Hanford Site response and rock conditions must be adequately
    considered.

-   Given the definition of the postulated sources and associated
    parameters, source-to-site attenuation relationships and proper
    amplification studies (including randomized profiles, a new
    probabilistic seismic hazard analysis, and seismic design response
    spectra) would be developed.

Attachment

**Attachment**

**Waste Treatment Plant: Ground Motion Criteria Issues and Their
Resolution**

1.  All of the anticlines were formed as part of the same stress field,
    and all are faulted on the north flank (reverse). There is evidence
    that one or two (maybe more) are capable. Why would all of the
    anticlines and the associated faults not be considered capable in a
    probabilistic analysis? (Closed)

2.  It does not appear that the plunging Yakima Ridge anticline has been
    considered even though it plunges beneath the site, and the adjacent
    and parallel anticlines are faulted and sources of seismic activity.
    (Closed)

3.  The 200 East area appears to be on a "fault" block bounded on the
    north by the east-west capable Gable Mountain anticline and fault
    and on the south by the Rattlesnake-Wallula trend anticline and
    fault (previously judged as capable). To the west and running
    north-south across the anticlines is the Hog Ranch feature. In
    between these two east-west features lies the east-west plunging
    Yakima Ridge, about which very little is known. Should this setting
    be treated somewhat differently than the normal approach allowed by
    a conventional probabilistic analysis? (Closed)

4.  Since the faults are classified as reverse faults and there is a
    strong possibility that there may be many blind faults, should the
    Waste Treatment Plant (WTP) vertical ground motion be enhanced?
    (Closed)

5.  The Geomatrix report (*Probabilistic Seismic Hazard Analysis, DOE
    Hanford Site, Washington*, WHC-SD-W236A-TI-002, Rev. 1A, October
    1996 ) appears to gloss over the effect of a single higher slip rate
    on one fault, as would be expected with a typical probabilistic
    study. On the other hand, if the higher slip rates estimated by one
    of the Geomatrix report panel experts (West) are valid, and if they
    are indicative of all of the faults associated with the anticlines,
    the impact would be highly significant for the probabilistic results
    as well. The validation study (*Validation of the Geomatrix Hanford
    Seismic Report for Use on the TWRS Privatization Project*,
    RPT-W375-RU00004, Rev. 0 dated March 17, 1999) makes the statement
    that "the regional experts stand by the slip rates of the Geomatrix
    Study . . ."; however, no counterarguments against West's higher
    slip rates are provided. (Closed)

6.  The Washington Public Power Supply System 2 Project deterministic
    analysis and the Geomatrix Probabilistic Analysis recognize capable
    faults within 5 to 10 km of the WTP. Discuss the potential for
    surface rupture at or near the site. (Closed)

7.  It appears that documentation of a comprehensive amplification study
    is not available. In view of the types and location of the events
    that drive the probabilistic analysis, are other studies available
    for review? The use of California attenuation data for the Hanford
    Site is no longer considered accepted practice. At present, a
    patchwork of analyses has been used (with no single stand-alone
    study that applies specifically to the 200 East area). Should a new
    analysis be considered that would be similar to the approach taken
    at the Savannah River Site, with source definition and random
    vibration theory applied to the actual attenuation path and actual
    soil column? (Open)

8.  The spectral amplification ratios (e.g., H1 to S2 Generic) are
    provided in Appendix A of the Geomatrix report (*Probabilistic
    Seismic Hazard Analysis, DOE Hanford Site, Washington*,
    WHC-SD-W236A-TI-002, Rev. 1A, October 1996 ) on log-log plots of
    spectral amplification ratio versus frequency. These plots do not
    appear to support the conclusion that the site responses for the 200
    East area and the generic California site are the same. In fact,
    they are considerably different at some periods, with the Hanford
    Site showing more amplification. (Open)

9.  Explain how the computer codes used in the analysis were verified
    and validated. Are public-domain versions of the codes available?
    (Closed)

10. Provide a list of the experts mentioned in the validation report
    (Validation of the Geomatrix Hanford Seismic Report for Use on the
    TWRS Privatization Project, RPT-W375-RU00004,Rev. 0, dated March 17,
    1999). (Closed)

11. Explain and discuss the weighting factors used for the attenuation
    relationships for both Appendix A of the Geomatrix report
    (*Probabilistic Seismic Hazard Analysis, DOE Hanford Site,
    Washington*, WHC-SD-W236A-TI-002, Rev. 1 A, October 1996 ) and the
    validation report (*Validation of the Geomatrix Hanford Seismic
    Report for Use on the TWRS Privatization Project*, RPT-W375-RU00004,
    Rev. 0, dated March 17, 1999). (Closed)

12. The DOE standard Natural Phenomena Hazards Assessment Criteria,
    DOE-STD-1023-2002, requires a historical check (using deterministic
    methods) of the probabilistic analysis. Since historical seismicity
    is low in the area of the site (numerous small events but with
    capable faults), it would appear that a deterministic check is
    appropriate given the number of capable faults that drive the
    probabilistic analyses. Has a deterministic check been considered?
    (Closed)

[^1]: SHAKE 2000 is an updated version of the SHAKE-A Computer Program
    for Earthquake Response Analysis of Horizontally Layered Sites,
    Earthquake Engineering Research Center, Report No. UCB/EERC-72/12,
    University of California, Berkeley, December 1972.