ML20147D365

Discusses Status of Trench Closing at Vallecitos & Examination of Trenches by NRC & Other Agencies.Recommends That GE Be Allowed to Backfill Trenches 1,2 & 3 & the Large Boreholes Now Dug,W/Encl Comments for 771202 Getr Meeting

ML20147D365
Person / Time
Site:	Vallecitos File:GEH Hitachi icon.png
Issue date:	11/30/1977
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	Stello V Office of Nuclear Reactor Regulation
References
NUDOCS 7812190231
Download: ML20147D365 (5)

Text

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,,, s 'k NUCLEAR REGULATORY COMMISSION 3 .3 )M j WASHINGTGN, D. C. 20$5L

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'% . . . . . # NOV 3 0 1977 MEMORANDUM FOR: V. Stello, Jr., Director, Division of Operating  !

Reactors FROM: H. R. Denton, Director, Division of Site Safety and Environmental Analysis

SUBJECT:

TRENCH CLOSING - VALLECITOS NUCLEAR CENTER (CETR)

PLANT NAME: General Elect.ric Test Reactor DOCKET NUMBER: 50-70 RESPONSIBLE BRANCHES: EEB, ORB-1 PROJECT MANAGER: A. Burger During a staff visit to the GETR site on November 16, 1977, General Electric Company personnel requested that they be allowed to backfill the trenches made for geologic investigations. We have also been notified by General Electric in the attached letter of G. D. Hoggatt of GE to A. Schwencer of NRC dated November 28, 1977, that the trenches will be filled on November 30, 1977 unless a valid reason is provided to leave them open. NRC and USGS personnel examined trench 1 on Octobot 13, 1977. Trenches 1 and 2 were examined by NRC, USGS and Calitornia Division of Mines and Geology (CDMG) personnel on October 22, 1977. NRC personnel inspected trenches 1, 2 and 3 on October 29, 1977 accompanied by two ACRS consultants. Representatives of the NRC, CDMG and the U. S. Corps of Engineers examined trenches 1, 2 and 3 again on November 16, 1977. It is our understanding that representatives of the USGS visited the site on November 28, 1977.

The licensee has mapped the trenches and we have preliminary copies available. In addition, we and the licensee have photographed features in the trenches. Although we consider it unlikely, these trenches could '

be re-excavated at a later date if necessary. We therefore recommend that General Electric Company be allowed to backfill trench 1, 2 and 3  ;

and the large diameter boreholes excavated to date. 1

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/ w H. R. Denton, Director i Division of Site Safety and Environmental Analysis Office of Nuclear Reactor Regulation

Attachment:

As stated cc: w/ attachment K. Coller Burger L. Barrett D. Eisenhut R. Hofmann J. Donohem I

W. Gammill R. Jackson A. Schwencer gg1S1

COMMENTS FOR GETF. MEETING 12/2/77 .

Purpose:

Evaluate Potential for Surface faulting at theaGETR site Pass concerns on to UE Express Problems Express Investigations needed to aid in resolving problem Problems A. As expressed in show cause order

1. Mapped location of the Verona fault

, 2. Thrust offset observed in trenches

3. Structural relationship of the Verona to the Calaveran fault 4 Regional tectonic setting Entire response to show cause order in surface faulting area is based on the premise that the Verona fault as postulated does not exist.

Investigations to date have shed new light on our understanding of the site geology - but present evidence is not conclusive.

At this point in our review we are not in a position to support con-clusion that denies the existence of a Verona fault. Sufficient investigations have not been accomplished to date to rhow that such a fault does not exist.

LANDSLIDES

1. Evidence for the existence of large, old landslides includes:

a. photointerpretation of landforms

b. shear planes and low angle thrust f eatures observed in trenches and borings near base (toe?) of proposed slide

c. jumbled nature of subsurface naterials and shears observed in trench 2.

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2. Evidence for landsliding is not conclusive because:

a. headscarp boundaries have not been supported by trenching

b. lateral shear zones have not been observed in trenches to define the limits of the slide l c. the primary slip surface has not been sufficiently located

d. un1ts of stable bedrock have not been shown to be discontinuous across slide boundaries

e. . units (beds) of stable bedrock have not been correlated with units in slide mass - sequences would be the same'

f. rotation of beds has not been demonstrated

g. the mechanism for mass movement has not been conclusively established, i.e. stream erosion of toe, more humid paleo-climate', breached resistant cap exposing materials susceptible to sliding

h. observed shear zones have not been correlated with primary and secondary slide masses

1. the age of soils offset in trench one has not been established,  ;

nor has the age of the landslide,

j. other geomorphic explanations of arcuate escarpments have not been addressed or evaluated, i.e. stream meanders, terraces, faulting w/ secondary sliding, etc.

VERONA FAULT

, 1. Evidence for the existence of the Verona Fault includes:

a. prominent south-facing scarp

b. generally linear, sharp break in topography

c. unexplained linear features in site area

d. seeps and ponds along linear feature

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e. thrust offset along shear planes exposed in trenches

f. . difference in elevation @-* 450') between Livermore gravels on either side of sharp break in topography

g. active local and regional tectonic setting and possible '

association of linears with Calaveras, Williams and/or Las Posit as Faults

h. existing geologic maps and texts of Vickerey, Hall, Herd, Cal. Dept. Water Resources , GETR

1. stratigraphic relationships on either side of proposed fault (Texas Company's Foley No. 1 well)

2. At the present time we cannot conclude that the Verona fault as postulated does not exist because: 1

a. thrust offsets observed in trenches may or may not be due to >

lands 11' ding. Trenches have not been dug along the proposed fault trace in areas where landsliding definitely does not exist (i.e. to the northwest under Qt alluvium)

b. local geology has not been mapped in detail

c. subsurface geology is complex and poorly understood at present

d. structural and stratigraphic relationships of geologic units are poorly understood in site. area

e. geomorphology of area is poorly understood - origin of anomalous landforms have not been evaluated

f. photo-linears have not been trenched or explained

g. origin of seeps and ponds have not been explained

h. soils offset in trench 1 have not been dated

1. thrust of fset has not been dated

j. resistant gravel unit east of the site has not been dated or I stratigraphically related to the Livermore gravels i

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- 4-9 Summary In our view, at the stage of our review, the situation is one of con-flicting hypotheses. One hypothesis proposes f aulting as the primary genetic cause of the features observed in the site area. This hypothesis -j has been forwarded by a number of geologists who have worked in the site region and the NRC staff. . Alternate hypotheses have been of fered which,'in essence, ascribe to erosion and mass wasting as the primary I genetic cause of the features observed in the site area. This hypo- ,

thesis is supported by data acquiredand evaluations made by General Electric Company consultants during the past two months. i At the present time we do not feel that sufficient data has been pro-vided which will allow us to conclude that the latter hypothesis is valid.

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