**\[DNFSB Letterhead\]**

September 7, 2006

The Honorable James A. Rispoli

Assistant Secretary for Environmental Management

U.S. Department of Energy

1000 Independence Avenue, SW

Washington, DC 20585-0113

Dear Mr. Rispoli:

The Defense Nuclear Facilities Safety Board (Board) received a letter
from the Department of Energy's Office of River Protection (DOE-ORP)
dated June 28, 2006, regarding the ability of the design of the
facilities at the Waste Treatment and Immobilization Plant (WTP) to
withstand potential earthquakes. The letter requested that the Board
acknowledge that issuance of the WTP Structural Design Criteria,
Revision 10, warranted closure of the ground motion criteria and
structural engineering issues raised by the Board.

In its October 17, 2005, letter to the Secretary of Energy, the Board
stated that the interim criteria (now referred to in WTP design
documentation as the Revised Ground Motion \[RGM\] criteria) provide a
reasonably conservative basis for validating the existing design and
construction of the plant. This conclusion was based on a detailed
technical review of the material provided in a report prepared by
Pacific Northwest National Laboratory, *Site-Specific Seismic Site
Response Model for the Waste Treatment Plant, Hanford, Washington*
(PNNL-15089, February 2005). This report provided ground motion
estimates considering a wide range of soil and rock properties under the
WTP site, including an assessment of ground motion uncertainties. As
noted in the PNNL report, these ground motion uncertainties are
significant. The Board's conclusion that the RGM criteria provide a
reasonably conservative basis for validating the design was predicated
on a conservative selection of soil and rock properties to address those
recognized uncertainties. The Board's conclusion was consistent with
DOE's decision to endorse the revised ground motion spectra.

It is important to recognize that design basis ground motions based on a
probabilistic seismic hazard analysis (PSHA), consistent with DOE
standards, must explicitly address legitimate differences of scientific
opinion on many of the key inputs, such as seismic sources, rates of
earthquake occurrence, and ground motion models. These legitimate
differences of scientific opinion translate into important uncertainties
in the numerical PSHA results. This inevitable fact, recognized by DOE
in the 1996 PSHA for the Hanford Site, remains true today, and is one
key reason that the RGM criteria were conservatively defined. A
substantial further increase in the ground motion at WTP (recognizing
that the RGM currently is up to 38 percent larger than that previously
assumed) would imply that ground motions for Hanford approach those
associated with higher seismic hazard environments, such as California.
Given current PSHA information and geology of the Hanford Site, such a
conclusion should be strongly challenged.

The Board reiterates its belief that the RGM criteria provide a
reasonably conservative basis for validating the design of WTP and
believes that the RGM criteria should be used to complete the design.

The current project Structural Design Criteria, Revision 11, provide
requirements and guidance that address the structural issues raised by
the Board. However, the details of the application of the Structural
Design Criteria in the structural analysis and the structure's predicted
response to the RGM are still being developed by the contractor. Thus
the Board has not reviewed these details, but will do so as soon as they
are available. The details and results of these structural analyses
should also be provided in updates to the Summary Structural Reports for
the High Level Waste and Pretreatment facilities. The Board expects that
its review of this information should be reasonably straightforward. The
structural engineering issues raised by the Board will remain open until
DOE-ORP submits the Summary Structural Reports and the Board can
evaluate their adequacy.

Sincerely,

***A. J. Eggenberger***

***Chairman***

c: Mr. Roy Schepens

Mr. Mark B. Whitaker, Jr.