ML20147C558

Forwards Status Rept of Dse Review of Geology as It Relates to Potential for Surface Faulting of Getr Site.Data Is Incomplete & Does Not Allow Final Conclusions.Encl Request for Addl Info

ML20147C558
Person / Time
Site:	Vallecitos File:GEH Hitachi icon.png
Issue date:	12/13/1978
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	Stello V Office of Nuclear Reactor Regulation
References
771213, NUDOCS 7812180329
Download: ML20147C558 (9)

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, ,i'pn Moog% UNITEo STA (ES 4 4 NUCLEAR REGULATOllY COMMISSION f, .%.) '

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WASHINGTON, D C. 20555 t / ,

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DEC 13 G7 4

MEMORANDUM FOR: V. S tello , Jr. , Directo r Division of Operating Reactcrs  :

FROM: Harold R. Denton, Director Division of Site Safety and ,

Environmental Analysis '

SUBJECT:

TECHNICAL ASSISTANCE REQUEST - NOVEMBER 18, 1977 -

REVIEW OF'GE'S RESPONSE TO SHOW CAUSE ORDER J

1 PLANT NAME: General Electric Test Reactor 4

DOCKET NUMBER: 50-70 RESPONSIBLE BRANCH: EEB, ORB-1

, PROJECT MANAGER: A. Burger

, REQUESTED COMPLETION DATE: December 15, 1977 Enclosed is a report of the status of our review of the geology as it relates to the potential for surface faulting at the GETR site. The conclusions contained therein are based on a limited review of all information acquired to date. The enclosed requests for additional

, information are not intended to be comprehensive, but a timely response to these requests would aid us in our short term evaluation of the potential for surface faulting. f

, ,> p.a f .: /,( g Harold R. Denton, Director Division of Site Safety and Environmen'tal Analysis Of fice o f Nuclear Reactor Regulation

Enclosure:

. As stated cc w/ enc 1:

K. Coller D Elaenhut Schwencer

• A. Burger C. Stepp R. Hofmann R. Jackson L. Barrett' J. Donahew D. Swanson M. Wohl b 1218 0 .3c.7 7

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, . l STATUS OF REVIEW GE TEST REACTOR SITE /VALLECITOS NUCLEAR CENTER

, DECEMBER 7, 1977 1'

Background

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Introductory background information is contained in the staff's l

stTtus of review, " Assessment of Geology and Seismology at the General l

l Electric Test Reactor Site - October 24, 1977."

Since the issuance of the Order to Show Cause by the Commission on October 24, 1977, we have made two visits to the Vallecitos Nuclear Center to examine the results of investigations undertaken by-the licensee. ' On these visits, we participated in field trips and examined trenches, large diameter borehotes, aerial photographs and newly-acquired topo-graphic maps. More specific details are contained in trip reports dated November 7, 1977 and November 16, 1977. In view of the licensees' pro-posed landslide mechanism for the generation of the young fault offsets

, observed in trenches 1 and 2, we asked that the U. S. Corps of Engineers and the Cal!.fornia Division of Mines and Geology provide personnel to review the available information. They have viewed the exposures in the trenches and have expressed their views verbally at the meetings. The general feeling expressed was that the thrust offsets observed in trenches 1 and 2 are probably the result of a large landslide, but at this time the presence of faulting cannot be ruled out. On December 2, 1977, at a meeting in Bethesda, the licensee made a presentation of all infor-mation gathered to date to the NRC staf f.

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In response to NRC's show cause order, General Electric. Company sub-m1tted a report on November 11, 1977- entitled, " Response to NRC order to Show Cause dated 10/24/77." The findings of this report with regard to the. potential for surface faulting in the site area is that, "from

- all evidence available to date it is concluded that the Verona fault as postulated does not exist." This conclusion is based on the l l following:

1. Evidence presented in support of a fault either does not stand up I' under careful scrutiny or is better explained by other processes. l

2. A thrust fault with the location and or1entation as postulated would 4

be a un1que and unusual feature in the context of other structures i

a in the San Andreas-Hayward-Calaveras fault system.

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3. The topographic and geomorphic expression of the Vallecitos and La Costa Valleys and ridge surfaces to the north can be explained by I geologic processes other than uplif t along a thrust fault.

1 i j Current Staff Position

! We have completed a review of the limited data provided in the res-1

- ponse to the show cause order together with information provided to us y

at meetings and site visits. The entire response to the show cause order i

in the area of surface faulting is based on the premise that the Verona f ault as postulated does not exist. Investigations to date have shed

' new light on our understanding of the site geology. We now find strong 4

evidence for large scale lands 11 ding in the site vicinity and the fault offsets found in trenches 1 and 2 could be caused by lands 11 ding. The

. Licensee has not, however, provided information that would support the conclusion that' the Verona f ault does not exist.

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4 At this point in our review we are not in a position to support a con-clusion that denies the existence of a Verona fault. Sufficient investi-gations have not been accomplished .to date to show that such a fault i

j does not exist and that there is not a potential for surface faulting in the GETR site area. This conclusion is based on the following obser-l vations. I

1. Verona Fault .

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

landsliding. Investigations have not been undertaken along the proposed fault trace in areas where lands 11 ding definitely does not exist to the northwest of the CETR site.

b. a prominent south-facing scarp and topographic break does exist in the site area. Ascribing the origin of this scarp solely to mass vasting and erosion is not supportable based on the available data.

c. The active local and regional tectonic setting (i.e. Calaveras f ault, . Livermore Valley) and existing geologic maps and texts of Vickery, Hall, Herd, General Electric Co. and California Depart-ment of Water Resources support the existence of the Verona fault and>other faults in the site vicinity.

d. The local geology has not been mapped in detail, the structural and stratigraphic relationships of geologic units in 'the area are

'poorly understood, and the subsurface geology is complex and poorly understood at present.

e. the geomorphology of area is poorly understood - origin of anomalous

. landforms have not been_, evaluated. -

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f. photo-linears in the immediate GETR site area have not been trenched or explained g, the origin of seeps and ponds in the sice have not been explained

' h. a resistant gravel unit east of the site has not been dated or

> stratigraphically related to the Livermore gravels.

2. Landslides

a. Evidence for the existence of large old landslides includes: l l

1. photointerpretation of landforms i l

2. shear planes and low angle thrust features observed in trenches and borings near the base (toe?) of the proposed slide l

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3. jumbled nature of subsurface materials, and presence of rotated blocks and shear surfaces as observed in trench 2. l l

h. Evidence for landsliding is not conclusive because: l

1. the headscarp boundaries have not been supported by trenching i

2. lateral shear zones have not been observed in trenches to define the limits of the slide

3. the primary slip surface has not been sufficiently located 4 units of stable bedrock have not been shown to be discon-tinuous across the slide boundaries and they have not been correlated with units in slide mass.

. 5. the mechanism for mass movement has not been conclusively established, i.e. oversteepening of valley walls by stream erosion, more humid paleo-climate, breached resistant. cap

' exposing materials susceptible to sliding.

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6. the age of soils offset in trench one has not been estab-lished, nor has the age'of the proposed landslide. If lands 11 ding has occurred in the area and the landslide is l 1

older than the soils offset, then the observed thrust 1

features must be attributed to some other more recent l me.chanism (e.g. thrust faulting). Also, soils may be dated i

at an age when more humid climates u ere known to exist in the site area which would tend to sup. cort the lands 11 ding hypothesis. l

7. observed shear zones have not been correlated with primary and secondary slide masses. l 1

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

i To the southeaat of GETR the licensee's mapping effort in the route 84 valley (north-south trending valley to the southeast of the site and route 84) has generated significant new information with regard to a southeasterly projection of a Verona fault. A moderately well-cemented conglomerate rock unit can be mapped along a ravine and can be shown to be continuous and unfaulted across the projected trace of both Herd's and Rall's mapped locacion of the Verona fault. The licensee believes that this conglomerate is a basal unit of the Livermore gravels. We generally concur with the licensee based on our limited review of avail-able information, but better understanding of the stratigraphic relation-ships is needed together with dating of the marker unit.

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r The continuity of this unit in this area is very significant because it severely restricts the southeasterly projection of a Verona fault. In  !

l our v1ew, it is very unlikely that a Verona fault with several hundred feet of vertical movement could cut across this ravine and connect with the Williams fault to the southeast. If the Verona fault is a thrust fault as we have postulated, however, it could swing to the north along route 84 and connect with the Las Positas fault zone as mapped by Herd (1977). Several prevalent linears can be observed on aerial photographs 1

of this area but s a do not, at present, have the detailed geologic mapping

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necessary to evaluate the presence or absence of f aulting in thia area.

At this stage of our review, the data do not resolve the conflicting interpretations of geologic features in the site area. One hypothesis proposes faulting as the primary genetic cause of the features (e.g.

topograph1c scarp, linear features, offsets) observed in the site area.

This hypothesis has been put forward by a number of geologists who have worked in the site region and by the NRC staff. An alternate hypothesis has been offered which, in essence, ascribes to erosion and mass wasting as the pr1 mary genetic cause of the features observed in the site area.

This hypothesis is supported by data acquired and evaluations made by General Electric Company consultants during the past tio months. At the present time we do not feel that sufficient data has been grovided which will allow us to conclude that the latter hypothesis is valid.

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- Request for Additional Information At the December 2,~1977, meeting we were asked if any additional information could ~be provided to aid us in our evaluation of the potential

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Though we have not received the

for surface faulting in the site area. )

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Licensee's geological studies in. response to our October 24, 1977, p

position (to be submitted by ' January 1,1978) we offer the following comments based on our visits to the site and conversations with the Licensee's consultants.

1. The area between GETR and the well-cemented gravel bed to the south-

east-should be investigated and geologically mapped especially in the vicinity of highway 84 to provide ~ evidence-for the stratigraphic .

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, and structural relationships of the area. Particular attention should i

be paid to the possibility of fault 1ng in' that area. , Provide

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assurance that the Verona fault does not bend to the northeast in the vicinity of highway 84 and connect with the Las Positas fault, e

l A trench or trenches across prevalent airphoto linears would also be useful.

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[j. 2. Provide evidence of stratigraphic and struc,tural relationships of bedrock materials along the Verona Fault northwest of GETR in areas shownbobeunaffectedbylandsliding. Subsurface investigations I should include trenching of fault traces ,linears, and projections of linears in the alluvium immediately northwes t of the escarpment.

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i Provide further information on the site area.

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3. Provide an explanation for the two airphoto linears which are visible in the vicinity of l the site pond. The most direct method of analyzing these features

could be accomplished through trenching. A suggested location for one tren.ch would be at the north . topographic break in the hillslope l

immediately adjacent to the site pond.

4. Definitive evidence must be provided to show that the thrust of fsets observed in trenches 1 and ? are not of tectonic origin. Since landsliding is proposed,

• 3 .imits of the' slide masses must be defined and supported by trenching or exposures of, for example, headscarps, lateral shear zones and toes and a reasonable demenstration that the primary slip surface can be correlated with the observed thrusts.

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