ML19294B044

Comments on J Farris 791227 & 800123 Ltrs Questioning Excavation Work.Depth of Soft Siltstone Layer Is 6-18 Ft Determined by Borings.Core Drilling Performed & Low Shear Wave Velocity Matl Removed

ML19294B044
Person / Time
Site:	Black Fox
Issue date:	02/14/1980
From:	Gallo J ISHAM, LINCOLN & BEALE
To:	Davis L NRC OFFICE OF THE EXECUTIVE LEGAL DIRECTOR (OELD)
References
NUDOCS 8002270064
Download: ML19294B044 (2)

Text

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fb ISHAM, LINCOLN & BEALE COUNSELORS AT LAW 1050 17'f' ST R E C T, N . W. SEVENTH FLOOra WAS HINGT ON, D. C. 2OO 3 G TE L E PHON E 202-833-9730 C HICAGO OF FIC E ONE FIRST NATIONAL PLAZA FORTY-SECOND FLOOR CH8CAGO,lLLINOe$ 60603 TELEPHONE 312-786-750 0 TE lex; 2-5288 February 14, 1980 L. Dow Davis, Esquire Office of the Executive Legal Director U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Dow:

I have Joe Farris' letters of December 27, 1979 and January 23, 1980, wherein he poses certain questions concerning the excavation work on Black Fox Station, Unit 2.

It may be helpful if I set forth for your edification my layman's understanding of the situation.

My letters to the Licensing Board and parties of October 23, 1979 and January 2, 1980 provided advice on the need to overexcavate the foundation araa for Unit 2. The information attached to the January 2 letter demonstrates that although tP, need to "overexcavate" may not be routinely encountered, no health and safety question is presented by the need to conduct such activities at Elack Fox. This information serves also as a basis to answer Joe's questions.

The first question -- How deep does the soft silt-stone formation go? -- is easily answered. The depth of the soft siltstone layer within the Unit 2 area varied from approximately six feet in the northeast section of the excavation to approximately 18 feet in the southwest section.

The depth of the soft siltstone layer was initially deter-mined (second Farris question) by borings which were made prior to the excavation of that siltstone. The actual depth was confirmed during the foundation verification process which occurred during excavation. The verification process included detailed inspection of the entire foundation surface, verification testing of the excavation floor material and removal of the unacceptable material.

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With respect to Joe's third question -- has core drilling been done to determine whether another siltstone layer exists below the one in question? -- core drilling extending to a depth of about 190 feet below the Unit 2 excavation level was performed during the geological inves-tigation of the site. Core drilling identifies some material underlying the excavation floor as siltstone. However, the examination and test results of this siltstone indicated it was competent bearing material for structures, and that it was not the soft variety of siltstone, i.e., low strength, high compressibility, low shear wave velocity material, which was removed from the excavation.

Finally Joe's letter of January 23 questions whether the selection of the 19 valve, random actuation SRV loading represents the most appropriate baseline case for the determining structural response and soil-structure interaction effects. It is my understanding that this SRV case is indeed the bounding case (see pages 3.8-55 and 3.8-55a of the attachment to my letter of January 2, 1980).

Sincerely,

. . ,

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0Joseph Gallo CC: Black Fox Service List